Author: ourworldunderthewaves

by Matthew Norton

Life can be hard in the ocean. It’s a theme I’ve returned to multiple times while writing these articles, mainly because different species find different ways to meet the challenge, often through millions of years of innovation through evolution. And then you have certain animal groups who seem to have barely changed since the time of the dinosaurs, perhaps in their case natural selection decided that the old ways were the best. Horseshoe crabs are one such group who predate the dinosaurs (so far as we know) and, despite appearances, are more closely related to spiders and scorpions than ‘true’ crabs. That said, I’ll continue to call them crabs for the sake of clarity (which is probably why the name ‘horseshoe crab’ has persisted to this day).

The ‘horseshoe’ part of their name comes from the round, U-shaped head that houses most of the precious organs under a single armour plate. On the underside, the crabs have five pairs of walking legs and in front of all that there is a sixth pair of claws, called chelicerae, that work like arms for grabbing food and directing it towards the mouth. Except they have no teeth, jaws or suitable mouthparts for breaking up their food into manageable chunks. Instead they use spines at the base of their legs, called gnathobases, to crush and tenderise their food before it’s collected by the chelicerae. Think of it like squeezing an orange between your thighs. 

As for defending themselves from predators, horseshoe crabs don’t seem to have much of an arsenal. They may have spines along the sides of their body, but their intimidating looking tail is primarily used for flipping themselves upright when crawling along the seabed, or steering themselves whilst swimming. The shell does effectively cover their entire body, but from personal handling experience, this layer of armour appears to be paper thin. Although this particular horseshoe crab was long dead and dried out, which may have rendered it thinner and weaker than it would otherwise be. 

But if we look past the conventional methods of protection, we might just find that horseshoe crabs have some sly tricks up their sleeve. For example, they have ten eyes spread around their body which come in different sizes and are fitted out for different functions (see the box jellyfish article for another example). They’re mainly used for finding mates and tracking the lunar cycle, but they could also warn of approaching danger. There is also some evidence to suggest that mangrove horseshoe crabs and tri-spine horseshoe crabs possess an effective poison called tetrodotoxin to dissuade possible predators (see the pufferfish article). 

Whatever defences horseshoe crabs may or may not possess, they do at least have the sense to breed in large numbers. A wise strategy given how easily distracted and vulnerable many animals can be while they’re ‘on the job’. In the case of the Atlantic horseshoe crab, they tend to gather between late spring and early summer and during the high tides. From there the males can home in on a potential mate by using their large compound eyes (relative to their other eyes and receptors), or from pheromones released by the female. But when they do actually meet, the mating process becomes an arduous process that is prone to turning into a complete farce. 

The main source of contention, for the males at least, is that the eggs can only be fertilised after the female has laid them. So as far as establishing paternity is concerned, it’s a first come, first served basis with the first male endeavouring to keep his place in the queue by literally riding on the female’s back. Evolution appears somewhat skewed in the male’s favour by equipping them with specially modified claws to maintain their grip and making them only two thirds of the size of a female. Still, I’d imagine the females would tire of this burden rather quickly as they climbed up onto the beaches, ready to deposit their eggs. 

Even then, a male’s success is far from assured. Over eager males may attempt to knock off a riding male, which may be what brought about the aforementioned riding claws since natural selection is bound to favour males who can hold on for longer. At the nesting site itself, there is always the chance for a few sneaky ‘satellite’ males to make their ‘contribution’ to another couple’s brood. With up to around 4,000 eggs in a single cluster, possibly accumulating to 100,000 eggs over an entire breeding season from a single female, it’s probably worth giving it a go. The sheer number of eggs might seem like an excessive effort on the female’s part, but a large proportion will be eaten by coastal seabirds such as red knots, ruddy turnstones and sanderlings.

Between their prehistoric appearance and the difficulties they face, horseshoe crabs might seem out of place in the modern world. An assumption that is unlikely to be helped by the fact that the group has only four living species to its name. And yet they persist, still able to hold their own like an ageing action hero returning to a franchise that was long thought finished. They’re still here so they must be doing something right. 

From a human perspective

Like many other animals from the ocean, horseshoe crabs have been harvested for centuries to fulfil a number of our needs. Delaware Bay, on the Eastern coast of the United States, where hundreds of thousands of Atlantic horseshoe crabs come to breed, has a particularly long history of this enterprise. Reports from early European settlers state how Native Americans would catch them for food and craft them into tools and soil fertiliser. The latter ultimately led to over a million horseshoe crabs being taken and utilised as cancerine fertiliser, an industry that thrived from the 1870s to the mid 20th century. But even as this came to an end, interest grew in using horseshoe crab meat as bait for whelk pots and American eel fishing. 

Moving further forward in time, horseshoe crabs have also proven useful in medicine, for within their bright blue blood there are incredibly effective immune cells called amoebocytes. Exceptionally sensitive to toxic bacteria, these amoebocytes react to their presence by creating a clot that immobilises the bacteria, isolating it from the rest of the crab’s body. This makes their blood ideal for testing vaccines, medicines and medical equipment for bacterial contamination. This is called the Limulus Amebocyte Lysate (LAL) test after the Atlantic horseshoe crab or the Tachypleus amebocyte lysate (TAL) test when the blood of an Asian species is used. 

The effectiveness of the LAL/TAL test is well documented, but as with all uses of horseshoe crabs, past and present, overexploitation is a serious concern. As it stands, the Tri-spine horseshoe crab is listed as “Endangered” by the IUCN, while the Atlantic horseshoe crab is “Vulnerable” and the other two species are “Data Deficient”. Proper regulation can help, but this can be difficult to achieve when you have competing interests, a lack of usable data and the interplay of fishing laws between different countries complicating matters. And let us not forget that direct fishing isn’t the only issue that horseshoe crabs have to deal with because of us humans. Climate change, pollution and habitat loss (especially on and around their nesting beaches) will pile on the pressure even more. 

Fortunately, there is a work around for some of these problems. In the 1990s, a group from the University of Singapore developed a synthetic alternative to the LAL/TAL test by cloning a molecule from horseshoe crab blood. This was called Recombinant Factor C (rFC) and, in theory, it should be the perfect solution. Yet these synthetic tests are yet to be widely used in some parts of the world, perhaps because the necessary ingredients aren’t widely available, or perhaps because some countries and organisations are slow to change their practices. The USA is a notable example since at least 700,000 crabs were bled to supply LAL tests in 2021 alone. 

But again, there are reasons to be optimistic. Returning to Delaware Bay, the area’s importance for nesting horseshoe crabs has not gone unnoticed. In 1999, the Ecological Research & Development Group (ERDG) launched a programme to encourage local communities to declare their beaches as horseshoe crab sanctuaries. One such sanctuary (among the 16 miles worth declared) is the colourfully named Slaughter Bay, which proudly displays its status on their official government website. If Atlantic horseshoe crabs are considered with such adoration and pride in an area so critical to their survival, then surely there is hope for the future of their species. 

As marvellous as horseshoe crabs are, the protection they need isn’t just for their sake. There are plenty of animals that rely on them for food, from small fish and hermit crabs to sharks and loggerhead turtles. Their eggs are also a crucial food source for migrating birds like rufa red knots, who might not even make it to the Canadian Arctic tundra without this crucial fuel stop. Even the shell of a horseshoe crab can provide a hard surface for animal like barnacles and slipper limpets to hang on to while their digging activities can rework and refresh the seafloor to the benefit (or detriment) of other species. No species in this world can live in complete isolation, not even us. 

Sources

Wikipedia. 2023. Horseshoe crab. https://en.wikipedia.org/wiki/Horseshoe_crab#. Last accessed 11/07/2023

The National Wildlife Federation. Horseshoe Crab. https://www.nwf.org/Educational-Resources/Wildlife-Guide/Invertebrates/Horseshoe-Crab. Last accessed 11/07/2023

Smithsonian’s National Zoo & Conservation Biology Institute. 2022. 10 Incredible Horseshoe Crab Facts. https://nationalzoo.si.edu/animals/news/10-incredible-horseshoe-crab-facts. Last accessed 31/07/2023

Maryland Department of Natural Resources. Horseshoe Crab Anatomy. https://dnr.maryland.gov/ccs/Pages/horseshoecrab-anatomy.aspx. Last accessed 31/07/2023

Kungsuwan et al. 1987. Tetrodotoxin in the horseshoe crab Carcinoscorpius rotundicauda inhabiting Thailand.

Zhu et al. 2022. Tetrodotoxin in Asian horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus across different life stages from northern Beibu Gulf, China

Brockmann. 1990. Mating behavior of horseshoe crabs, Limulus polyphemus

NOAA. 2018. Horseshoe Crabs: Managing a Resource for Birds, Bait, and Blood. https://www.fisheries.noaa.gov/feature-story/horseshoe-crabs-managing-resource-birds-bait-and-blood. Last accessed 08/08/2023

Kreamer and Michels. 2009. History of horseshoe crab harvest on Delaware Bay

Krisfalusi-Gannon et al. 2018. The role of horseshoe crabs in the biomedical industry and recent trends impacting species sustainability

Pavid. 2021. Horseshoe crab blood: the miracle vaccine ingredient that’s saved millions of lives. https://www.nhm.ac.uk/discover/horseshoe-crab-blood-miracle-vaccine-ingredient.html. Last accessed 31/07/2023

Gauvry et al. 2022. LAL/TAL and Animal-Free rFC-Based Endotoxin Tests: Their Characteristics and Impact on the Horseshoe Crab Populations in the United States and Asia

Eisner. 2023. Coastal biomedical labs are bleeding more horseshoe crabs with little accountability. https://www.npr.org/2023/06/10/1180761446/coastal-biomedical-labs-are-bleeding-more-horseshoe-crabs-with-little-accountabi. Last accessed 31/07/2023

John et al. 2021. Conservation of Asian horseshoe crabs on spotlight

Wang et al. 2020. Future of Asian horseshoe crab conservation under explicit baseline gaps: A global perspective

IUCN Red List. https://www.iucnredlist.org/search?query=horseshoe%20crab&searchType=species. Last accessed 29/08/2023

Maloney et al. 2018. Saving the horseshoe crab: A synthetic alternative to horseshoe crab blood for endotoxin detection

Berkson and Shuster Jr. 1999. The horseshoe crab: the battle for a true multiple‐use resource

Delaware Government Information Centre. History. https://slaughterbeach.delaware.gov/history/. Last accessed 08/08/2023

Delaware.gov. 2022. FAQs about Delaware Bay Rufa Red Knots and Horseshoe Crabs. https://documents.dnrec.delaware.gov/fw/conservation/Del-Bay-Red-Knot-Horseshoe-Crab-FAQ.pdf. Last accessed 08/08/2023

The Ecological Research & Development Group (ERDG). Backyard Stewardship™: Coastal Communities Define Their Shared Habitat as a Horseshoe Crab Sanctuary. https://www.horseshoecrab.org/act/sanctuary.html. Last accessed 08/08/2023

ecoDelaware. Slaughter Beach, an official horseshoe crab sanctuary. http://www.ecodelaware.com/place.php?id=358#:~:text=Slaughter%20Beach%20is%20an%20ERDG,an%20official%20Community%20Wildlife%20Habitat. Last accessed 08/08/2023

Florida fish and wildlife conservation commission. Facts About Horseshoe Crabs and FAQ. https://myfwc.com/research/saltwater/crustaceans/horseshoe-crabs/facts/#:~:text=Many%20fish%20species%20as%20well,%2C%20horse%20conchs%2C%20and%20sharks. Last accessed 08/08/2023

Botton. 2009. The ecological importance of horseshoe crabs in estuarine and coastal communities: a review and speculative summary

Image sources

James St. John. 2013. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Limulus_polyphemus_(Atlantic_horseshoe_crab)_(Sanibel_Island,_Florida,_USA)_2.jpg

Alexander Hüsing from Berlin, Deutschland. 2007. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Mesolimulus_walchi.jpg

Rhododendrites. 2017. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Horseshoe_crab_in_Silver_Sands_State_Park_(21090).jpg

Gee. 2017. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Horseshoe_Crab_chelicerae_and_gnathobases.jpg

Rachel Oh. 2012. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Horseshoe_crab_eyes.jpg

Rhododendrites. 2019. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Horseshoe_crabs_mating_(57352).jpg

Marshall Astor from San Pedro, United States. 2007. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Horseshoe_Crab_in_Si_Racha.jpg

Decumanus. 2004. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Delaware_bay_map.jpg

DataBase Center for Life Science (DBCLS). 2022. [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]. https://commons.wikimedia.org/wiki/File:202210_Tri-spine_horseshoe_crab_donating_blood.svg

All other images are public domain and do not require attribution.

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

What is the difference between an animal and a plant? What is different about how one interacts with the world around them compared to the other? Perhaps the most obvious answer is that plants tend to exist and grow from one spot whereas animals are noticeably more mobile. On land, this appears to be a fairly clear cut boundary between plant and animal life, but in the ocean the line is more blurred. There are seaweeds that exist as floating masses and multitudes of different animal species who cement themselves to one spot for almost their entire lives. The latter lifestyle is only possible because they are effectively living in a whirling soup of microscopic plankton and other associated morsels. Why waste the energy when you can simply wait for your dinner to come to you? 

It’s a strategy that, while undoubtedly efficient, can quickly falter if the local food supply dries up, or a persistent predator approaches, or the local habitat becomes uninhabitable. Assuming the individual animal had the chance to spawn and spread out their young, then its untimely death may be inconsequential in the grand scheme of things. Still, it would be  nice to have an escape strategy, no matter how temporary. This is where feather stars come in, with plant-like arms that they can stretch out and filter food from the passing water, but who can also relocate themselves if the need arises. Perhaps feeling a little smug in the process, if they are capable of feeling this kind of emotion. 

Feather stars, also known as crinoids, are part of the echinoderm phylum, a group that also includes starfish, sea urchins and sea cucumbers. But while their cousins tend to use rows upon rows of sticky ‘tube feet’ to keep them attached to the seabed, feather stars are usually found anchored on harder surfaces (e.g. rock, corals) using hook-like structures called cirri on the base of their body. These hooks can be engaged and then disengaged at will to allow the feather stars to either crawl about, or even swim (depending on the species) to find a new home. A swimming feather star can make for some strangely hypnotic viewing. 

For the sake of clarity, it is worth mentioning that there is another group of crinoids that are commonly referred to as ‘sea lilies’. These creatures are usually stalked and immovable throughout their lives whereas feather stars generally possess these stalks during their younger years before ultimately ditching them. I say ‘usually’ and ‘generally’ because some sea lily species also possess detachable cirri and this whole thing about how the stalks separate the two groups of crinoids has a rather messy history in the fossil record. Alas, nature rarely conforms to the strict groupings we try to assign to it.

But if we look a little closer, we find that even when the body is fixed in one place, temporarily or permanently, there are still things to do and movements to make. For example, each arm of a feather star is adorned with side branches called pinnules which contain multitudes of tube feet that sieve out the microscopic morsels of food and flick them towards a central feeding groove. These grooves are filled with tiny, hair-like cilia that shuffle the food towards the mouth and perform any necessary sorting between the edible and non-edible pieces. It’s like there are hundreds of little workers working a single conveyor belt.

The workload required to keep themselves fed can also pose quite the conundrum to a feather star, should they detect a potential predator. Flinch too soon and they could lose valuable feeding time and a prime location by flying away from what might prove to be a false alarm. Even if the threat is confirmed, a tactical retreat won’t necessarily be the first defence they might call upon. Feather stars can avoid the notice of predators through camouflage and particular feeding habits (there is some evidence to suggest they feed more at night to avoid predators). They may also deter predators with thick, densely branched arms, thick and spiky pinnules and/or the use of chemicals that give them an unpleasant taste. And should a predator overcome all of this and attack before the feather star can escape, they are able to regenerate certain parts of their body and survive otherwise fatal wounds. Even the loss of their digestive system can be tolerated by directly absorbing nutrients from the water as a temporary measure. 

In conclusion, there seems to be numerous advantages to the flexible lifestyle of a feather star. Compared to their stalked sea lily cousins, they have more species alive today (550 v.s. 80) and can be found in shallow waters and the deep sea whereas sea lilies appear restricted to the latter, with the shallowest species living 100m below the surface. This may simply be because feather stars have more control over their destiny throughout their lives, whereas most benthic species can only disperse across meaningful distances as very young larvae. Some play it safe and stick to areas that are already flooding with their own kind while others venture out to new grounds, risking it all with little chance of success. But feather stars can adopt both strategies, they can be both prudent and pioneer with the ability to change their mind at a moment’s notice. 

From a human perspective

Like many sea creatures, crinoids have found themselves thrust into various corners of human history and culture. For example, the fossilised remains of sea lily stalks can be found, preserved in the rock but broken down into little segments, like star shaped polo mints. They have been described as fairy coins, star stones and St. Cuthbert’s beads, in reference to a seventh century priest who reportedly held them as part of a rosary. 

But these remains also hold clues to a time long before our species evolved into being, with sea lily fossils being found within the rocks of modern day seasides and in rocks that are now far away from the ocean. The latter indicates that a now terrestrial (i.e. dry land) environment was once underwater, possibly hundreds of millions of years ago. 

One of the most famous examples is the Burgess Shale, a site located high in the Canadian Rockies but which is full of fossilised sea creatures. And among these finds are the remains of soft bodied animals, which makes these shale rocks especially valuable since it’s usually only the hard parts, such as bones and shells, that survive the fossilisation process.

Crinoid fossils are particularly useful fossils to find, for various reasons. Their presence alone can all but confirm that the area was a saltwater environment at that particular time in earth’s history, simply because echinoderms are incapable of surviving in freshwater. A quality not shared by other animal groups (e.g. vertebrates, molluscs, annelid worms) who have seawater and freshwater species among their ranks. Also, the fact that they are still alive today means we can use modern day crinoids as proxies (i.e. guides) for understanding how their ancestors might have lived. Combined with other parts of the puzzle we can glean from other fossils and preserved materials, we can at least begin to deduce how the entire prehistoric ecosystem might have functioned. But as well founded as the conclusions of one researcher, or more likely one research group, may be, they are almost always open to debate and interpretation. You could argue that palaeontology (the study of fossils) itself is mostly educated guesswork based on the sparse information at our disposal. 

So why do we go to all this trouble? Scientific curiosity aside, there is a lot we can learn from species and whole communities that came and went millions of years ago. Particularly the warning signs of catastrophes like mass extinctions, which can be traced and dated through (relatively) sudden disappearances of whole animal groups in the fossil record. Assuming we can also measure the environmental conditions from around the times of these sudden disappearances, which we can do in a roundabout way, then we can begin to understand the triggers behind them. Of the five mass extinctions throughout the earth’s history (that we know of) the data suggests that rapid changes in global temperature and the levels of certain gases, like oxygen and carbon dioxide, were heavily involved in at least some of them.

If you’re thinking this all sounds familiar, it’s because our planet is currently going through a period of rapid climate change, due to the increased levels of greenhouse gases, such as carbon dioxide and methane, that we are churning out into the atmosphere. In 2023, it might sound somewhat redundant to state this out loud, but there are those who still deny that climate change is happening, or that’s a major problem, or that it’s being caused by our burning of fossil fuels (among other unsustainable practices). It’s tempting to dismiss these people as idiots, or suggest that they have a vested interest in ignoring the overwhelming scientific consensus. But while this might be true for a select few individuals, other ‘climate sceptics’ may have misinterpreted the facts or been misinformed about the issue, leading them to reach conclusions that, while extremely flawed, do have some logic behind them. 

A point that climate skpetics sometimes make is that climate change is simply a normal part of the earth’s cycle. This is true, even going back several hundred thousand years, there have been natural fluctuations in global temperature and the concentration of greenhous gases. But where this argument falters is with the speed at which these changes are happening today compared with back then. One study, published in 2017, estimated that human activities are heating up the Earth around 170 times faster than natural warming alone. While the exact figure might be debated, most would agree that human-induced climate change is fast outpacing anything that came before. This is especially worrying when you consider that a mass extinction event, by definition, occurs when species are going extinct faster than replacements can be found to fill the holes they leave behind in the natural world. And at this rate, the sixth mass extinction we seem to be heading for could be the most challenging yet for life on this planet. 

But let us try and put all the doom and gloom to one side for a moment and end on a positive note (nothing will ever get done otherwise). It is important that we recognise the effect that we, as a species, are having on this planet and the kind of world we’re heading for if we don’t change our ways. But therein lies a slither of hope. We can change, it’s in our power to avert disaster. Just think of everything that humanity has achieved in the last 100 years, things that were once thought of as impossible to achieve and insane to dream of. We invented the internet, travelled out into space and developed cures for otherwise fatal diseases. We may be the cause of everything that threatens the natural world today, but if we can find a way to work with nature then we can make ourselves a critical part of the solution.

Sources

NOAA. What is Sargassum?. https://oceanexplorer.noaa.gov/facts/sargassum.html. Last accessed 28/04/2023

Wikipedia. 2023. Crinoid. https://en.wikipedia.org/wiki/Crinoid#. Last accessed 01/04/2023

Rafferty. 2008. feather star. https://www.britannica.com/animal/feather-star. Last accessed 29/04/2023

Rodriguez et al. 2016. sea lily. https://www.britannica.com/animal/sea-lily. Last accessed 29/04/2023

Messing. 2017. Crinoids: Deep-sea Lily-like Animals. https://oceanexplorer.noaa.gov/okeanos/explorations/ex1711/logs/dec7/welcome.html. Last accessed 28/04/2023

Mladenov and Chia. 1983. Development, settling behaviour, metamorphosis and pentacrinoid feeding and growth of the feather star Florometra serratissima

Stevenson et al. 2017. Predation on feather stars by regular echinoids as evidenced by laboratory and field observations and its paleobiological implications

Macurda and Meyer. 1974. Feeding posture of modern stalked crinoids

Meyer. 1973. Feeding behavior and ecology of shallow-water unstalked crinoids (Echinodermata) in the Caribbean Sea

Macurda and Meyer. 1983. Sea lilies and feather stars

Holland et al. 1986. Particle interception, transport and rejection by the feather star Oligometra serripinna (Echinodermata: Crinoidea), studied by frame analysis of videotapes

Birenheide and Motokawa. 1996. Contractile connective tissue in crinoids

Mladenov. 1983. Rate of arm regeneration and potential causes of arm loss in the feather star Florometra serratissima (Echinodermata: Crinoidea)

Smith et al. 1981. Amino acid uptake by the comatulid crinoid Cenometra bella (Echinodermata) following evisceration

Warner and Woodley. 1975. Suspension-feeding in the brittle-star Ophiothrix fragilis

Meyer and Macurda Jr. 1977. Adaptive radiation of the comatulid crinoids

Baumiller and Gahn. 2003. Predation on crinoids

Charmouth Heritage Coast Centre. Crinoids. https://charmouth.org/chcc/crinoids/. Last accessed 11/04/2023

British Geological Survey. Crinoids. https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/crinoids/. Last accessed 11/04/2023

Lotzof. Snakestones: the myth, magic and science of ammonites. https://www.nhm.ac.uk/discover/snakestones-ammonites-myth-magic-science.html. Last accessed 31/05/2023

Foster. 2021. You can find ‘fairy coin’ fossils in the UK for a free day out with the kids. https://www.dailystar.co.uk/travel/travel-news/you-can-find-fairy-coin-24802936. Last accessed 31/05/2023

Goodman. Crinoid Star fossil – 30 pieces – fairy coins – Great gift for collectors. https://www.etsy.com/uk/listing/1120840107/crinoid-star-fossil-30-pieces-fairy. Last accessed 31/05/2023

Morris and Whittington. 1979. The animals of the Burgess Shale

Smithsonian National Museum of Natural History. The Burgess Shale. https://naturalhistory.si.edu/research/paleobiology/collections-overview/burgess-shale. Last accessed 01/06/2023

Butterfield. 1990. Organic preservation of non-mineralizing organisms and the taphonomy of the Burgess Shale

University of Kansas. Crinoids. https://geokansas.ku.edu/crinoids. Last accessed 01/06/2023

Boeuf. 2011. Marine biodiversity characteristics

Donovan. 2020. Train crash crinoids revisited

Berardelli and Niemczyk. 2021. The Great Dying: Earth’s largest-ever mass extinction is a warning for humanity. https://www.cbsnews.com/news/great-dying-permian-triassic-extinction-event-warning-humanity/. Last accessed 12/06/2023

Bauska. 2022. Ice cores and climate change. https://www.bas.ac.uk/data/our-data/publication/ice-cores-and-climate-change/. Last accessed 12/06/2023

Alley et al. The Vostok Ice Core. https://www.e-education.psu.edu/earth104/node/1267. Last accessed 23/06/2023

Riebeek. 2005. Paleoclimatology: the Oxygen Balance. https://earthobservatory.nasa.gov/features/Paleoclimatology_OxygenBalance. Last accessed 23/06/2023

Begum. 2023. What is mass extinction and are we facing a sixth one? https://www.nhm.ac.uk/discover/what-is-mass-extinction-and-are-we-facing-a-sixth-one.html. Last accessed 12/06/2023

Earthday.org. 2021. 6 ARGUMENTS TO REFUTE YOUR CLIMATE-DENYING RELATIVES THIS HOLIDAY. https://www.earthday.org/6-arguments-to-refute-your-climate-denying-relatives/. Last accessed 13/06/2023

Gaffney and Steffen. 2017. The anthropocene equation

Image sources

Jay Nadeau, Chris Lindensmith, Jody W. Deming, Vicente I. Fernandez, Roman Stocker, David Liittschwager. 2006. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Marine_microplankton.jpg

Philippe Guillaume. 2009. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Trampa_mortal.jpg

National Oceanic and Atmospheric Administration (NOAA). 2010. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:NOAA_stalked_crinoid.jpg

William I. Ausich. 1998. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:Crinoid_anatomy.png

Preview_H. 2007. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Feather_Star_1.jpg

Charles G. Messing. 1987. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:Ambulacrum_Crinoidea.png

Ria Tan from singapore. 2012. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Podia_of_a_red_feather_star.jpg

James St. John. 2017. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Crinoid_stem_in_fossiliferous_limestone_(Lower_Mercer_Limestone,_Middle_Pennsylvanian;_Rt._16_roadcut_near_Trinway,_Ohio,_USA)_6_(33213509646).jpg

Chmee2. 2011. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:Prurez_stonky_lilijce_v_Dalejskym_profilu.JPG

Edna Winti. 2013. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Burgess_Shale,_Yoho_National_Park.jpg

Michael S. Engelderivative work: Kevmin. 2010. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:Leptofoenus_pittfieldae_(male)_rotated.JPG

Ryan Somma. 1980. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Burgess_Shale_Fossils.jpg

Helle Astrid Kjær. 2017 [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]. https://commons.wikimedia.org/wiki/File:Shallow_ice_core_drilling_(danish_Hans_Tausen_drill)_1.jpg

65Eq. 2017. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:VostokIceCore.jpg

NASA’s Scientific Visualization Studio, Key and Title by uploader (Eric Fisk). 2020. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Change_in_Average_Temperature_With_Fahrenheit.svg

All other images are public domain and do not require attribution.

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

Who doesn’t enjoy a sunny day by the seaside? The fresh sea breeze, the crisp water washing in from the ocean’s edge, the moist sand caressing the spaces in between your toes. True, the sand can be an absolute nightmare to get rid of afterwards, but in that moment there is a pure, unspoiled bliss about it. Depending where you are, the coastline can take many other forms, from pebble and shingle beaches to jagged rocky shores that hold a splattering of saltwater pools at low tide. Even in predominantly sandy shores, there are sometimes isolated chunks of rock. And where there is rock, there is a good chance that you will find one the best known animals of the intertidal world. Limpets.

There are many species of limpets, from the seaweed munching blue-rayed limpet to the air breathing pulmonate limpets. But around the United Kingdom, and much of northwest Europe, the most common species is the appropriately named ‘Common limpet’. It might seem pointless for me to state this fact, but there are a lot of species, from a lot of animal groups, who are supposedly common. Such as the ‘Common seal’, the ‘Common starfish’ and the ‘Common sea urchin’. But many of these names were assigned to their species decades, if not centuries ago. And as we know, a lot can change in that time, especially when the human race is involved. 

Common or not, these limpets are tougher and more resourceful than some might expect from a little sea snail. Like any other animal on the seashore, they have to contend with the dry air and scorching sunshine every time the tide goes out. When this happens, the aim of the game is to conserve and retain as much water as possible. The limpet strategy towards this end is to clamp themselves down to the rock with their strong, muscular foot, thereby cutting themselves off from the outside world until the sea returns.

For added security, limpets will also carve a ring into the rock that is a perfect fit for their shell, rough edges and all. This ring is called their ‘home scar’ because wherever they may venture when the tide is in, they will at least try to return to the same ring before the sea moves back again. Assuming nothing catastrophic happens, they can usually retrace their steps back by using a trail of mucus slime they leave in their wake. Some studies even suggest that limpets can think strategically and modify their feeding excursions based on certain environmental factors. For example, limpets have been observed to stray further from their home scars during spring tides, when the rising tide pushes further inland compared to the more modest neap tides. But this is just one example, foraging behaviour can also be affected by a limpet’s position on the shore, the kind of habitat they find themselves in and individual preferences. 

Finding food is relatively straightforward for a limpet, for the rock on which they live is usually covered in a film of algae and other microscopic organisms on which they gorge themselves. Their weapon of choice for extracting their food is a radula, a feeding organ that most molluscs possess in one form or another, which in limpets is basically a tongue with built in scraping teeth. What is particularly remarkable about a limpet’s radula is the tensile strength of these teeth, which even outperforms the incredibly durable silk threads produced by spiders. The secret appears to be goethite, an iron oxide compound usually found in rusting metal, but which limpets have moulded into tiny nanofibers that reinforce their teeth. We humans have done something similar with glass fibres, which we have used to reinforce concrete and plastic polymer mixes and to create materials with a greater tensile strength than steel. 

In conclusion, limpets are brilliant examples of how even the smaller animals in the sea can surprise us with their ingenuity. We humans can be prone to believing that we are the smartest animals on the planet by a huge margin. We have certainly compensated for our squishy bodies and lack of sharp claws with tools and machines that suit our needs. But in some cases, our designs and inventions bear striking similarities to what the natural world had already evolved millions upon millions of years ago. Back when humanity was little more than a speck in the future of a very distant ancestor. 

From a human perspective

The ocean is, and always has been, a major influence on our existence on this planet. Even something as intrinsically man made as modern warfare can include aspects that originated in the natural world. This feels a particularly relevant topic at the moment, given the ongoing war in Ukraine. While there won’t be any further references to that particular conflict in the following paragraphs, I would like to stress that this section is not intended to celebrate, or glorify violence and death on this scale, or any scale really. Instead, this is more of an acknowledgement of how the ocean can be a source of inspiration in every human endeavour. Including those we hope never to experience first hand. 

Where do limpets fit into this picture you may ask? They are one of the most straightforward examples of ocean inspired weaponry because of the limpet mine. First deployed during the second world war, these weapons are designed to be stuck to the hull of an enemy vessel using magnets instead of powerful sucking muscles. Typically, they are applied manually by divers and fitted with a delay timer to allow them to clear out before detonation. Assuming all goes to plan, the result would be catastrophic damage to its target.

Some sources might claim that limpet mines are primarily used to disable a vessel rather than outright sinking it. But that didn’t exactly pan out when the Rainbow Warrior, Greenpeace’s flagship vessel, was sunk in 1985. It was due to sail out to the Mururoa Atoll to protest against French nuclear tests in the region, but instead it was hit by two explosions to the stern while docked in Waitematā Harbour, Auckland, New Zealand. 

Since there was only a small engine and no explosive materials on board, it wouldn’t have taken much imagination to suspect foul play. Especially when divers investigated the remains of the Rainbow Warrior and recovered the remnants of limpet mines. Two French secret agents were soon caught attempting to leave the country and they ultimately plead guilty to manslaughter for the attack and were sent back to France in 1986 to serve their lengthy prison sentences. 

The French government dismissed them as ‘rogue agents’ in an attempt to distance themselves from the attack. But further evidence has emerged in the years since, especially from documents released in 2005, that proves it was all an official operation to deter the nuclear protests by force. In the end, they made considerable compensation payments to both New Zealand and Greenpeace, the latter of whom put the money towards building a new Rainbow Warrior, which was eventually launched in 1989. Even so, the country’s damaged reputation from this incident wasn’t entirely salvaged. The two implicated agents only served two years of their respective seven and ten year sentences. A move that prompted a b******ing from the United Nations and probably caused further strain between the two countries.

Moving away from limpet mines, there are other examples of marine animals inspiring  real life weapons of war. Excoet missiles, which first entered service in 1975 and are designed to fly towards its target at very low altitude, are based on, and named after the flying fish. Going back further in time, or to certain museums, you might find sawfish snouts repurposed into swords. Or turtle shells repurposed into shields.

But it doesn’t always have to be this way. There can be peaceful applications for nature’s inventions. Jellyfish for example, their slow and steady swimming style has been adapted for underwater drones, complete with hydraulic ‘tentacles’. More stable and energy efficient than other designs, these jellyfish drones could be used for monitoring the oceans, particularly the environments surrounding vulnerable habitats like coral reefs, or exploring shipwrecks and other submerged structures. They could still be used for military surveillance, but unlike a gun, mine, or missile, they can be used for so much more. 

And in the end, there are very few ideas or inventions that are inherently good or evil. It’s how they are applied that really matters. Take Darwin’s theory of evolution by natural selection. For decades now, it has formed the basis of how we understand the natural world and has been applied to our benefit, such as tackling the causes of antibiotic resistant bacteria. But throughout the first half of the twentieth century, it was also exploited and used to justify discrimination, forced sterilisation and genocide. Whatever ideas we come up with, inspired or not by the world around us, it is our responsibility to use them for the right reasons.

Sources

Fish and Fish. 2011. A student’s guide to the seashore. ISBN. 978-0-521-72059-5

The Marine Life Database. 2020. Limpet, Pulmonate. https://www.marinelife.ac.nz/species/732#:~:text=Identification%3A,or%20overgrown%20with%20other%20species. Last accessed 17/03/2023

British Sea Fishing. Common Limpets. https://britishseafishing.co.uk/limpets/. Last accessed 05/01/2023

Coleman and Hawkins. 2000. Limpet relocation from home-scars in relation to position in group

Garrity and Levings. 1983. Homing to scars as a defense against predators in the pulmonate limpet Siphonaria gigas (Gastropoda)

Little et al. 1988. Foraging behaviour of Patella vulgata L. in an Irish sea-lough

Santini et al. 2019. Barnacle cover modifies foraging behaviour of the intertidal limpet Patella vulgata

Gray and Hodgson. 1997. TEMPORAL VARIATION IN FORAGING BEHAVIOUR OF PATELLA GRANULARIS (PATELLOGASTROPODA) AND SIPHONARIA CONCINNA (BASOMMATOPHORA) ON A SOUTH AFRICAN SHORE

Gajera et al. 2022. Radular Morphology and Relationship Between Shell Size and Radula Size of Few Dominating Intertidal Gastropod Mollusks of Veraval Coast, Gujarat

Barber et al. 2015. Extreme strength observed in limpet teeth

The Editors of Encyclopaedia Britannica et al. 2019. Goethite. https://www.britannica.com/science/goethite. Last accessed 05/01/2023

Kodous. 2021. What’s the difference between glass fibre reinforced polymer (GFRP) and steel rebar? https://www.linkedin.com/pulse/whats-difference-between-glass-fibre-reinforced-polymer-kodous#:~:text=Glass%20fibre%20reinforced%20polymer%20(GFRP)%20%E2%80%93%20sometimes%20called%20glass%20fibre,epoxy%20or%20polyester%20thermosetting%20plastic. Last accessed 17/02/2023

Palmer. 2020. GLASS FIBER REINFORCED CONCRETE. https://www.concretenetwork.com/glass-fiber-reinforced-concrete/. Last accessed 17/02/2023

Tuf-bar. ADVANTAGES OF USING GLASS FIBER REINFORCED POLYMER (GFRP) REBAR. https://www.tuf-bar.com/advantages-of-using-glass-fiber-reinforced-polymer-gfrp-rebar/. Last accessed 17/02/2023

Ismay. 2019. What Are Limpet Mines, and How Do They Work? https://www.nytimes.com/2019/06/14/world/middleeast/limpet-mine-tanker-attack.html. Last accessed 17/01/2023

Australian War Memorial. Limpet Mine Mk 1. https://www.awm.gov.au/collection/C302932. Last accessed 17/01/2023

France 24. 2019. Limpet mines: classic maritime weapon. https://www.france24.com/en/20190620-limpet-mines-classic-maritime-weapon. Last accessed 17/01/2023

BBC News. 1985: Rainbow Warrior sinks after explosion. http://news.bbc.co.uk/onthisday/hi/dates/stories/july/10/newsid_2499000/2499283.stm. Last accessed 04/02/2023

Bremner. 2005. Mitterrand ordered bombing of Rainbow Warrior, spy chief says. https://web.archive.org/web/20070222110453/http://www.timesonline.co.uk/tol/news/world/article542620.ece. Last accessed 04/02/2023

NZHistory. Rainbow Warrior sunk by French secret agents. https://nzhistory.govt.nz/rainbow-warrior-sunk-in-auckland. Last accessed 04/02/2023

Willsher. 2015. French spy who sank Greenpeace ship apologises for lethal bombing. https://www.theguardian.com/environment/2015/sep/06/french-spy-who-sunk-greenpeace-ship-apologises-for-lethal-bombing. Last accessed 04/02/2023

Centre for strategic & international studies. 2021. Exocet. https://missilethreat.csis.org/missile/exocet/. Last accessed 04/02/2023

Military Leak. 2020. Exocet AM39 Airborne Anti-ship Missile. https://militaryleak.com/2020/04/11/exocet-am39-airborne-anti-ship-missile/. Last accessed 04/02/2023

The British Museum. Weapon. https://www.britishmuseum.org/collection/object/E_Oc-1794. Last accessed 04/02/2023

Simmons. 2005. Sawfish sword. http://www.vikingsword.com/vb/showthread.php?t=1005. Last accessed 04/02/2023

Flight-toys. 2020. https://www.flight-toys.com/artifacts/a27.html. Last accessed 04/02/2023

Reading Museum. Sword Sawfish snout. http://collections.readingmuseum.org.uk/index.asp?page=record&mwsquery=(%7Bsearch%7D=*%7Bjoseph%20stevens%7D)&filename=REDMG&hitsStart=7. Last accessed 04/02/2023

Hermens. 2020. The turtle’s carapace: a curious painting support or a battle shield? https://lookingthroughartblog.wordpress.com/2020/07/07/the-turtles-carapace-a-curious-painting-support-or-a-battle-shield/#:~:text=On%20this%20etching%20from%201633,use%20turtle%20carapaces%20as%20shields. Last accessed 04/20/2023

BBC News. 2014. Flying drone inspired by swimming jellyfish. https://www.bbc.co.uk/news/science-environment-25732293. Last accessed 17/02/2023

Innovation news network. 2021. Engineers create a jellyfish-inspired underwater robot for marine exploration. https://www.innovationnewsnetwork.com/engineers-create-a-jellyfish-inspired-underwater-robot-for-marine-exploration/8917/. Last accessed 17/02/2023

BBC News. 2018. Jellyfish robots to watch over endangered coral reefs. https://www.bbc.co.uk/news/technology-45574309. Last accessed 17/02/2023

Military.com. 2013. US Navy’s New Jellyfish Drone. https://www.military.com/video/logistics-and-supplies/military-equipment/us-navys-new-jellyfish-drone/2280091975001. Last accessed 17/02/2023

National Human Genome Research Institute. Eugenics and Scientific Racism. https://www.genome.gov/about-genomics/fact-sheets/Eugenics-and-Scientific-Racism. Last accessed 17/02/2023

History.com editors. 2018. Social Darwinism. https://www.history.com/topics/early-20th-century-us/social-darwinism. Last accessed 17/02/2023

Image sources

Muséum national d’histoire naturelle. 2020. [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]. https://commons.wikimedia.org/wiki/File:Patella_ulyssiponensis_(MNHN-IM-2000-4929).jpeg

Muséum national d’histoire naturelle. 2020. [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]. https://commons.wikimedia.org/wiki/File:Patella_depressa_(MNHN-IM-2000-4947).jpeg

Muséum national d’histoire naturelle. 2020. [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]. https://commons.wikimedia.org/wiki/File:Patella_depressa_(MNHN-IM-2000-4947).jpeg

Thomas Schoch. 2012. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Patella_vulgata_Madeira_2.jpg

Rosser1954. 2017. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Patella_vulgata_and_their_rock_imprints,_Saltcoats_Harbour,_Ayrshire,_Scotland.jpg

Auguste Le Roux.2013. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Patella_vulgata_broutage_3993.jpg

HM Government. 1939. [OGL v1.0OGL v1.0 (https://nationalarchives.gov.uk/doc/open-government-licence/version/1/)]. https://commons.wikimedia.org/wiki/File:Clarke_with_limpet_mine_in_swimming_position.jpg

Ot. 2004. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:RainbowWarrior-1985b.jpg

Tiraden. 2013. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:MBDA_Exocet.JPG

Auge=mit. 2019. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Sawshark_Saegehai_noBG.jpg

All other images are public domain and don’t require attribution.

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

For many of us, the seashore is an idyllic landscape where we can explore and relax with a cold ice cream. But for the sea creatures who actually live at this boundary between worlds, it’s one of the harshest environments on the planet. The dangers include overheating, drying out and environmental extremes that a watery existence would normally buffer against. But, nature always finds a way and some species have risen to this challenge so well that they seem to prefer life in the air, rather than the ocean. 

Fiddler crabs are a prime example since, unlike other seashore crabs, they wait until the tide has left the beach before emerging from their underground burrows to forage for food. They don’t often stray too far from a burrow, and so have the option to run back in if things get too hot out in the open. But they also need to scrounge enough from the sand to sustain themselves, so they employ a few tricks that allow them to bear the scorching heat. 

To some extent, these crabs don’t even need to try anything new, instead using methods of temperature resistance that have been tried and tested in other animals (or vice versa). These include heat shock proteins, which protect other proteins from being deformed and rendered useless by high temperatures, and dispersing heat through the evaporation of water from their shells (this is also why we humans sweat). 

But to truly thrive in such an environment, one must know their limits and react accordingly (natural selection tends to show no mercy to individuals who ignore this advice). Fiddler crabs are well aware of this and employ behaviours and on the spot changes to regulate their body temperature. Some are quite clever, such as changing their orientation to the sun and the colour of their shells to absorb as little sunlight as possible. Other behaviours are little more than common sense, such as running to a burrow when it really is getting too hot and avoiding parts of the beach that are too inhospitable, even for them. That said, fiddler crabs who think long term can gradually acclimatise to hotter areas through experience and physical changes that will enhance their heat resistance, such as growth in body size.

All these adaptations will come in handy during courtship, where male fiddler crabs will push themselves to the boundaries of what they can tolerate to impress a female (some things never change). Specifically, the males wave their large claws in the air, sometimes alone and sometimes as part of a group effort. A particularly energetic display may woo a lady crab, but it will also be exhausting for the male and expose them to especially harsh conditions. Not to mention running the risk of attracting unwanted attention from predators. But such feats of endurance and daredevilry might just be what the females are looking for.

The need for male fiddler crabs to stand out with their large claws is an example of ‘sexual selection’, where a feature evolves in one gender of a species to appeal to the other. This approach tends to work because it demonstrates that the most ‘attractive’ male can still survive despite the issues that come with carrying his big claw around and waving it in the air. This suggests that they carry exceptional genes for surviving the seashore and so would be a good father for the next generation of fiddler crabs.

From a human perspective

Fiddler crabs are one of my favourite sea creatures. Not only are they fascinating and important to the functioning of many seaside habitats, but they were also the subject of my first dissertation project back when I was a student studying marine biology. Which is why I saved them for this article, which is the 40th article I have published since starting this blog in late 2017. 

Their biggest influence on humanity in general is in their support of mangrove forests, which in turn can protect us from the ocean’s more destructive tendencies, such as tsunamis and coastal erosion. But since I have covered this in a previous article about mangroves, I decided to write about my experience working with fiddler crabs instead. 

The story begins at Plymouth University in the autumn of 2014, at which time I was in my second year and looking for volunteering opportunities for the following summer. This led me to an event on campus that had been organised by Operation Wallacea, who run and maintain research stations all over the world. My original intention was to join an existing research project, but the chance to do the research for my third year dissertation abroad was too good to pass up.

Several months later, I embarked on a mammoth journey that consisted of two international flights, two domestic flights, a convoy of cars and a short (ish) boat ride. The eventual destination was Hoga Island (also known as Pulau Hoga), a remote island in Indonesia. Despite being homesick and knocked back by the time zone difference, it was a beautiful spit of land in the middle of Wakatobi National park.

Of course, there are drawbacks to spending six weeks in such a remote location. For starters, the lack of running water meant we had to drink bottled water and shower with buckets of cold water. The heat was also pretty intense, and with no electricity in some areas, including the sleeping huts, I can guarantee there were plenty of sticky and sweaty nights.

The health and safety orientation we attended on arrival also highlighted the less trivial aspects of life on a tropical island. These ranged from diseases and dangerous animals to coral holes and the vulnerability of our location should earthquakes and tsunamis hit the region. The words “we will make you comfortable” were used on multiple occasions, although most dangers could be averted through appropriate precautions and common sense (i.e. don’t be an idiot).

Once that was out of the way, and we’d all had a chance to sleep off the jet lag, it was straight to the job at hand. The first week or two was spent getting to know the other researchers on the island and setting up and testing the equipment for my experiments. On more than one occasion, my original research plan had to be modified according to the resources we had available. 

With that done, it was time to hop over to the nearby island of Kaledupa to collect the crabs. On this brief expedition, I was lucky enough to be accompanied by a group of Indonesian students who were incredibly skilled at catching fiddler crabs as they bolted to the safety of their burrows. I meanwhile, was absolutely hopeless and only managed to catch a couple of them through dumb luck.

The crabs were taken back to Hoga and housed in a wet laboratory building located five minutes away (by foot) from the main site. There was a cleared path in the vegetation between the two areas, but this didn’t always prevent encounters with the island’s wildlife. Fortunately, they let me pass peacefully, as many animals will do so long as we respect their personal space. 

There were other students working on their own research projects in the wet lab, and while there was no strict ‘quid pro quo’ arrangement in place we were encouraged to help each other if we weren’t otherwise occupied. Towards the end of our time on the island, some of us went out for a bit of snorkelling. We didn’t stray far from the shore, but we still saw some beautifully coloured fish in the crystal clear water. The spectacle made up for the state I was in as water constantly leaked into my goggles and I struggled to use my flippers in a way that was even remotely effective.

The six weeks ended with a big party that involved alcohol, dancing on tables and a bonfire on the beach. The result I got from my research didn’t reveal anything particularly exciting, but it was, at the very least, a well executed piece of science, which is the most important part of any study, regardless of aims, results or where in the world the data is coming from. Still, it was an incredible experience to spend six weeks away from civilisation, albeit with some modern comforts (still can’t believe there was ice cream available on the island). I’d imagine that most people would like to get away from it all from time to time. 

Sources

Eliss. 1968. Transition from water to land in decapod crustaceans

Carlson et al. 2014. Density, Shell Use and Species Composition of Juvenile Fiddler Crabs (Uca spp.) at Low and High Anthropogenic Impact Salt Marsh Sites

Emmerson and McGwynne. 1992. Feeding and assimilation of mangrove leaves by the crab Sesarma meinerti de Man in relation to leaf-litter production in Mgazana, a warm-temperate southern African mangrove swamp

Osborne and Smith. 1990. Differential predation on mangrove propagules in open and closed canopy forest habitats

Meziane et al. 2002. Role of fiddler crabs of a subtropical intertidal flat on the fate of sedimentary fatty acids

Robertson and Newell. 1982. A study of particle ingestion by three fiddler crab species foraging on sandy sediments

Feder and Hofmann. 1999. Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Frenkel et al. 2008. Both heat shock and water deprivation trigger Hsp70 expression in the olfactory lobe of the crab Chasmagnathus granulatus

Somero. 2004. Adaptation of enzymes to temperature: searching for basic “strategies”

Barnwell. 1968. Comparative aspects of the chromatophoric responses to light and temperature in fiddler crabs of the genus Uca

Wilkens and Fingerman. 1965. Heat tolerance and temperature relationships of the fiddler crab, Uca pugilator, with reference to body coloration

Backwell. 2019. Synchronous waving in fiddler crabs: a review

Hews et al. 2021. Field-based body temperatures reveal behavioral thermoregulation strategies of the Atlantic marsh fiddler crab Minuca pugnax

Levinton. 2020. Thermal stress: The role of body size and the giant major claw in survival and heat transfer of a fiddler crab (Leptuca pugilator)

Darnell and Munguia. 2011. Thermoregulation as an alternate function of the sexually dimorphic fiddler crab claw

Allen and Levinton. 2014. Sexual selection and the physiological consequences of habitat choice by a fiddler crab

Takeda. 2006. Behavioural evidence for body colour signaling in the fiddler crab Uca perplexa (Brachyura: Ocypodidae)

Forward and Rittschof. 1994. Photoresponses of crab megalopae in offshore and estuarine waters: implications for transport

Frith and Brunenmeister. 1980. Ecological and population studies of fiddler crabs (Ocypodidae, genus Uca) on a mangrove shore at Phuket Island, western peninsular Thailand

Koch et al. Comparative population dynamics of four fiddler crabs (Ocypodidae, genus Uca) from a North Brazilian mangrove ecosystem

Mokhtari et al. 2015. Determination of key environmental factors responsible for distribution patterns of fiddler crabs in a tropical mangrove ecosystem

McNish. Who was Alfred Russel Wallace? https://www.nhm.ac.uk/discover/who-was-alfred-russel-wallace.html?gclid=Cj0KCQjwkIGKBhCxARIsAINMioLKTOqpye8B31FA3wpfUKOG8a2Mgcx8wEnxwyR5kGpj7khDF4HRIWYaAr7dEALw_wcB. Last accessed 14/09/2021

Image sources

Kathy. 2009. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Fiddler_crabs.jpg

Denise Chan from Hong Kong, China. 2006. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Fiddler_Crab_-_Australia.jpg

Kate Perez. 2019. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Fiddler_Crabs.jpg

Bernard DUPONT from FRANCE. 2014. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Calling_Fiddler_Crab_(Uca_vocans)_(15717078196).jpg

Thomas Brown. 2011. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Fiddler_Crab_(Uca_crassipes%3F)_(6263284060).jpg

All other images are public domain, or my own.

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

The ocean is full of animals who possess incredible strength and who are capable of feats of endurance that we couldn’t hope to match, not without the help of machines. Examples include the awesome punching power of mantis shrimp, the arduous migrations made by sperm whales and the exhausting patience of a saltwater crocodile as it lies in wait below the water’s surface. Though few creatures can match the sheer power and hunting prowess of the sharks. 

But even these powerful fish don’t spend all their time eating and making little sharks. Like many animals, they too need their down time and have no interest in burning up their energy reserves without good reason. To that end, sharks generally have a light skeleton, made mostly of cartilage, and a large liver full of oils that are lighter than water. Both of these adaptations make it easier for sharks to stay above the seafloor and out of the deep sea (unless that’s where they belong). Their skin is also covered in tiny little teeth (dermal denticles) which makes the animal more streamlined and able to swim faster.

Some sharks have gone even further in their evolution, fine tuning their biology so that they exert as little effort as possible. Sand tiger sharks (Carcharias taurus) are a great example, enhancing their buoyancy by swallowing air and holding it in their stomach. This trick allows them to hover in the water, barely moving until there is something good to eat, or they feel like stretching their fins a little. 

Other species, such as the nurse shark (Ginglymostoma cirratum), settle down on the seafloor for extended rest stops. During this time, they use powerful muscles in their mouth to manually pump water through their gills so they can breathe. Should the shark be covered in sand, they also have openings just behind the eyes (called spiracles) through which they can draw in water.

For many sharks, a nap on the ground isn’t an option. They have to keep swimming to keep ramming water through their gills, otherwise they will drown. But these species can still sort of sleep by turning off one side of their brain while the other side keeps the body moving and an eye out for danger and food. 

But are any of these sharks really sleeping? Or are they just in a state of quiet wakefulness? Truth be told, we’ll probably know since the only first hand experience we have of being asleep is as human beings. Assuming that sharks sleep like we do is a flawed approach at best, as is projecting any of our thoughts and experiences onto another species, a concept known as anthropomorphisation. Nonetheless, it can help to make science more widely accessible and encourage empathy with the natural world, so long as we don’t take it too far.

From a human perspective

Whether asleep, or quietly awake, a resting shark is still a shark and they should be approached with caution and respect. Even when docile, nurse sharks have been known to retaliate against divers and snorkelers who invade their personal space. Sand tigers have also occasionally clashed with humans over a tasty fish, despite their normally sluggish behaviour. 

But as large and powerful as sharks are, researchers need to get close to them, sometimes uncomfortably close, to get the data needed for wildlife management and conservation efforts. Such data is also in pretty high demand since a large number of shark species are still listed as ‘Data Deficient’ by the International Union for Conservation of Nature (IUCN). Meaning we don’t have enough information to really know if they are at risk, never mind what they might be at risk from. 

There are non-invasive methods we can use to study the lives of sharks with little to no interference. These include underwater censuses, baited cameras and environmental DNA samples, all of which can be used to estimate how many of each shark species there are in a given area. Carefully planned experiments in the wild can also reveal how sharks would behave in a given situation more accurately compared to testing their responses in an unnatural setting. 

But by capturing live sharks (hopefully temporarily) we can also measure their size, determine their gender and identify the species with greater accuracy. A quick glance might not always be enough to tell apart two or more similar looking species (see image above).

Having the shark in brief custody also offers the chance for more intimate measurements through blood and tissue samples. Such samples can reveal the concentrations of hormones and heavy metal pollutants in the shark’s body, the latter of which sharks are particularly vulnerable to since they can accumulate such toxins from their prey. Admittedly, we could take more samples from the insides of dead sharks, but non-lethal samples from living specimens can still indicate what toxins they have throughout their entire body. With the added bonus of not having to wait for a corpse to wash up, or relying on being able to get there while sampling is still viable.

Captured sharks can also be fixed with tags, usually on, or around the dorsal fin, so that their movements can be tracked post-release. It’s a method that has been used on sharks for nearly a century (although fish in general have been tagged for much, much longer), although these days sharks are often fixed with satellite tags that ‘ping’ their location every time they surface. As more and more sharks are tagged, the hope is that we can identify their migration routes and seasonal hotspots, particularly for endangered and elusive species, and then protect those areas as needed.

But for all the information they give us, the experience of being tagged and/or having samples taken from them is never going to be a pleasant one for the sharks. The best we can do is to carry on developing new techniques that minimise the stress and trauma inflicted on these animals. 

Fast capture techniques, such as snagging sharks by the tail, have already been tested as alternatives to more conventional techniques, such as netting and angling. But a better approach, certainly from an animal welfare perspective, would be to avoid taking sharks out of the water at all. Dart tags, attached to the end of a pole, or the bolt of a speargun, are already being used. As are biopsy probes for extracting tissue samples, both underwater and from the side of a boat, before immediately preserving them for later analysis. 

With all the technical challenges and ethical considerations around shark research, a top priority should be getting the very most of each set of data we get from each shark. An aim that can only be realistically achieved through collaborations between individuals and organisations from different professions and countries. The Cooperative Shark Tagging Program (CSTP) is a great example since it brings together anglers, commercial fisheries and scientists from the National Oceanic and Atmospheric Administration (NOAA). Since its inception in 1962, the program has tagged over 295,000 sharks from 33 species. 

I doubt that such a monumental feat could have been achieved without the thousands of volunteers who have contributed to this program. A true testament to what citizen science can achieve. 

Sources

Habeggar et al. 2012. Feeding biomechanics and theoretical calculations of bite force in bull sharks (Carcharhinus leucas) during ontogeny

Randall. 1977. Contribution to the biology of the whitetip reef shark (Triaenodon obesus)

Oceana. Longnose Sawshark. https://oceana.org/marine-life/sharks-rays/longnose-sawshark. Last accessed 18/07/2021

Shark Trust. Shark Anatomy. https://www.sharktrust.org/shark-anatomy. Last accessed 12/07/2021

Oceana. Sand Tiger Shark. https://oceana.org/marine-life/sharks-rays/sand-tiger-shark. Last accessed 12/07/2021

National Geographic. Sand Tiger Shark. https://www.nationalgeographic.com/animals/fish/facts/sand-tiger-shark. Last accessed 12/07/2021

French et al. 2018. Ginglymostoma cirratum. https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/ginglymostoma-cirratum/. Last accessed 12/07/2021

Castro. 2013. Must Sharks Keep Swimming to Stay Alive? https://www.livescience.com/34777-sharks-keep-swimming-or-die.html. Last accessed 18/07/2021

Whitney et al. 2016. The effects of temperature and swimming speed on the metabolic rate of the nurse shark (Ginglymostoma cirratum, Bonaterre)

Kelly et al. 2019. Evidence for sleep in sharks and rays: behavioural, physiological, and evolutionary considerations

Ritter. 2019. Is the Shark Just Drifting, or Does It Take a Quick Nap?

Rogers. 2016. How Do Sharks Sleep? https://www.sharksider.com/how-do-sharks-sleep/. Last accessed 12/07/2021

Aucoin et al. 2017. A new underwater shark capture method used by divers to catch and release nurse sharks (Ginglymostoma cirratum)

Shark Research Institute. 2005. SHARK SPECIES INVOLVED IN INCIDENTS. https://www.sharkattackfile.net/species.htm. Last accessed 12/07/2021

IUCN Shark Specialist Group. Frequently Asked Questions: Sharks, Rays, and chimaeras. https://www.iucnssg.org/faqs.html. Last accessed 09/09/2021

De Vos et al. 2015. Baited remote underwater video system (BRUVs) survey of chondrichthyan diversity in False Bay, South Africa

McCauley et al. 2012. Evaluating the performance of methods for estimating the abundance of rapidly declining coastal shark populations

Kilfoil et al. 2021. The influence of shark behavior and environmental conditions on baited remote underwater video survey results

Boussarie et al. 2018. Environmental DNA illuminates the dark diversity of sharks

Ritter and Amin. 2014. Are Caribbean reef sharks, Carcharhinus perezi, able to perceive human body orientation?

Ritter and Amin. 2012. Effect of human body position on the swimming behavior of bull sharks, Carcharhinus leucas

Martin. Shark Tissue Samples Needed to Assist Phylogenetic Research. http://www.elasmo-research.org/research/sampling.htm. Last accessed 03/08/2021

Save our seas foundation. Shark Share Global. https://saveourseas.com/project/shark-share-global/. Last accessed 03/08/2021

Stevens and Brown. 1974. Occurrence of heavy metals in the blue shark Prionace glauca and selected pelagic in the NE Atlantic Ocean

O’Bryhim et al. 2017. Relationships of mercury concentrations across tissue types, muscle regions and fins for two shark species

University of Miami. 2021. GPs for Sharks. https://sharkresearch.rsmas.miami.edu/research/projects/gps-for-sharks/. Last accessed 25/07/2021

Kohler and Turner. 2001. Shark tagging: a review of conventional methods and studies

Queiroz et al. 2019. Global spatial risk assessment of sharks under the footprint of fisheries

Ocearch. Shark Tracker. https://www.ocearch.org/tracker/. Last accessed 23/08/2021

Gleiss et al. 2009. A new prospect for tagging large free-swimming sharks with motion-sensitive data-loggers

Robbins. 2006. Evaluation of two underwater biopsy probes for in situ collection of shark tissue samples

Meyer et al. 2018. Simple biopsy modification to collect muscle samples from free-swimming sharks

Daly and Smale. 2013. Evaluation of an underwater biopsy probe for collecting tissue samples from bull sharks Carcharhinus leucas

NOAA. 2020. Cooperative Shark Tagging Program. https://www.fisheries.noaa.gov/resource/document/cooperative-shark-tagging-program. Last accessed 23/08/2021

NOAA. Tagging Instructions and Resources for Volunteers. https://www.fisheries.noaa.gov/new-england-mid-atlantic/atlantic-highly-migratory-species/tagging-instructions-and-resources-volunteers. Last accessed 23/08/2021

Image sources

Albert Kok. 2007. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Bull_shark_(2007).jpg

Pascal Deynat/Odontobase. 2011. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Denticules_cutan%C3%A9s_du_requin_citron_Negaprion_brevirostris_vus_au_microscope_%C3%A9lectronique_%C3%A0_balayage.jpg

Maniacduhockey. 2011. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Requin-taureau_sand_tiger_shark.jpg

Aquaimages. 2006. [CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)]. https://commons.wikimedia.org/wiki/File:Diver_and_Nurse_Shark_in_cave,_Monito_Island,_Puerto_Rico.jpg

Michelle Hedstrom from Arvada. 2008. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Carcharhinus_perezi_bahamas2.jpg

Elias Levy. 2014. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Great_White_Shark_(14730796397).jpg

Matthew T Rader, https://matthewtrader.com. 2018. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Whale_Shark_(Rhincodon_typus)_with_open_mouth_in_La_Paz,_Mexico.jpg

All other images are public domain and do not require attribution

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

The seafloor can create some rough terrain with jagged rocks, soft sands and sheer cliff edges being some of the obstacles that bottom dwelling animals must overcome to find food and escape predators. Crabs rise to the challenge with their jointed legs, as do octopuses with their sucking tentacles and lobe-finned fish with their thick, fleshy fins. But few animals are as capable at off roading as starfish (also called ‘sea stars’ for not being actual fish).

If you have ever visited an aquarium you may be aware of how starfish can climb up vertical surfaces, particularly glass windows, with ease. It’s a feat they achieve with the rows upon rows of tube feet they keep on the underside, both along each arm and around the middle. We often think of these tube feet as mere suckers, but starfish also use a chemical adhesive (i.e. glue) to strengthen their hold. That is, until powerful muscles, connected to the tubes of pressurised water that props up the whole starfish body, unsticks each tube foot and allows it to move forward.

It might seem a bit pedantic to focus on how exactly starfish hold on to a surface, but small details, like the inclusion of glue, can make a huge difference. For instance, there is evidence to suggest that a single tube foot can resist being dislodged no matter what angle it is pushed from. If starfish relied on suction alone, their predators, or competitors, may have greater success if they attacked from the side.

Sticky feet might also be more forgiving on those occasions where suckers would fail to get a good grip, whether it be due to extremely rough terrain or bad aim. And considering the number of tube feet that some species of starfish possess, mistakes are inevitable. For animals with effectively no brain, it’s amazing they can coordinate their movement at all.

Using glue to stick to surfaces is also going to have some drawbacks, otherwise everyone would do it. One possible issue could arise from the sticky ‘footprints’ they leave behind, which could betray their presence. In a previous article, I mentioned that many submerged surfaces are, over time, covered in a layer of organic material called a ‘biofilm’. The concoctions of chemicals it contains is a valuable source of information for starfish, who can read the biofilm with receptors built into their tube feet. But this can also be true of their enemies, including other starfish. 

Tube feet are useful pieces of kit for starfish, as well as their diverse cousins. But with such a diversity of owners, there is also a diversity in shape and structure. One source even mentioned a type of tube foot with a ‘knob’ end, as described from the suggestive shape of its tip under a microscope. It would seem that evolution’s tendency for tinkering with a core design can produce some odd results.

From a human perspective

Few sea creatures are as immediately recognisable as starfish. I have seen the joy they bring firsthand through my current job at the National Marine Aquarium in Plymouth (not affiliated with this blog). They bring joy to so many visitors, particularly those young children who run straight up to the tanks that have starfish stuck to the glass.

Their popularity can also be seen in the stories and works of literature that starfish have inspired. These include fables, poems and even non-fiction books about business management. 

The influence of starfish also extends into popular culture, with the most famous example being Patrick Star, the dimwittted, but lovable best friend of Spongebob Squarepants. He fits the general appearance of a starfish (minus the many tube feet), but Patrick’s character and quirks were also inspired by the real thing. Specifically, how starfish appear to be slow and dumb, only to surprise you with their active and aggressive lifestyle.

Starfish are also important in scientific research, particularly in a laboratory where they are relatively easy to breed and care for. There is particular hope for their role in stem cell research where, one day, we might be able to replicate a starfish’s ability to regenerate almost any part of their body. I very much doubt we can push this area of science into creating real life versions of Wolverine, Deadpool or any other comic book character gifted with super fast healing. But it could help to advance the treatment of medical conditions that can only be tackled sufficiently with stem cells.

Going back to how starfish move, there have been multiple projects to create ‘starfish robots’. Like other animal inspired robots, their designs replicate the shape and omnidirectional movement of the real thing. In many cases, the bulk of the starfish robot is made out of soft and flexible materials such as silicon. These would be closer to the constitution of real starfish compared to metal, or hard plastics.

If these artificial starfish were to be let loose on the seafloor (within reason) the ‘soft robot’ approach is probably the way to go. Considering the rough and unpredictable environments that real starfish have to contend with. Although, the ‘tube feet’ that one such robot starfish is equipped with are suckers only. An oversight that is probably common in the current roster of robot starfish designs as the inclusion of an onboard reservoir of synthetic glue, and a delivery system in each replicate foot, would surely be a logistical nightmare. 

As an addendum to the whole topic of robots and starfish, a few years ago there was a project to protect coral reefs from the destructive crown of thorns starfish by dispatching them with robots armed with lethal injections. I draw your attention to this in case you want to read more about starfish robotics. You may have to trawl through a few pages of headlines about robots killing starfish, like I did when I was researching for this article. 

But what would happen if these two branches of underwater robotics were brought together? We could end up with five legged terminators long before anything that resembles Arnold Schwarzeneggar. 

Sources

NOAA. 2021. Are starfish really fish? https://oceanservice.noaa.gov/facts/starfish.html. Last accessed 11/05/2021

IFL Science. This GIF Of A Starfish “Walking” Is Legitimately Disturbing. https://www.iflscience.com/plants-and-animals/viral-video-of-starfish-walking-across-a-beach-weirds-out-the-internet/. Last accessed 31/05/2021

Wikipedia. 2020. Tube feet. https://en.wikipedia.org/wiki/Tube_feet. Last accessed 16/05/2021

Smith. 1937. The structure and function of the tube feet in certain echinoderms

Hennebert et al. 2012. Echinoderms don’t suck: evidence against the involvement of suction in tube foot attachment

Thomas and Hermans. 1985. ADHESIVE INTERACTIONS BETWEEN THE TUBE FEET OF A STARFISH, LEPTASTERIAS HEXACTIS, AND SUBSTRATA

Kerkut. 1954. The mechanisms of coordination of the starfish tube feet

ChrisM. 2011. Secrets of the Starfish Sieve Plate & Madreporite Mysteries? aka What is that little circle on top?? http://echinoblog.blogspot.com/2011/01/secrets-of-starfish-sieve-plate.html. Last accessed 29/06/2021

BS Media. 2017. WATER VASCULAR SYSTEM IN STARFISH. https://www.bioscience.com.pk/topics/zoology/item/561-water-vascular-system-in-starfish. Last accessed 29/06/2021

Feder and Lasker. 1964. Partial purification of a substance from starfish tube feet which elicits escape responses in gastropod molluscs

Hennebert et al. 2013. Functional biology of asteroid tube feet

Kellogg, D. and D. Fautin 2001. “Crinoidea” (On-line), Animal Diversity Web. Accessed May 16, 2021 at https://animaldiversity.org/accounts/Crinoidea/

Wikipedia. 2021. Starfish. https://en.wikipedia.org/wiki/Starfish#In_legend_and_culture. Last accessed 07/06/2021

McKay et al. 2001. Gadi Mirrabooka: Australian Aboriginal Tales from the Dreaming. Libraries Unlimited. ISBN. 1-56308-923-8

Alyson-Wieczorek. 2006. Poems for the sea by Sigourney, L. H. (Lydia Howard), 1791-1865. https://archive.org/details/poemsforsea00sigoiala/page/136/mode/2up. Last accessed 07/06/2021

Meier. 2010. The Starfish and the Spider: 8 Principles of Decentralization. https://irevolutions.org/2010/01/09/starfish-spider-decentralization/. Last accessed 07/06/2021

Luke Alexander. 2019. Case Of The Sponge ‘Bob’ (Video 2005). https://www.youtube.com/watch?v=Pkw2NX4CfNw. Last accessed 22/06/2021

UCMP. Introduction to the Deuterostomia. https://ucmp.berkeley.edu/phyla/deuterostomia.html. Last accessed 13/06/2021

Dove. 2020. The Future of Human Healing Lies in the Brain of a Starfish. https://www.cmu.edu/news/stories/archives/2020/march/dahl-starfish.html. Last accessed 13/06/2021

Davydov et al. 1990. The Starfish Asterina pectinifera

Jin et al. 2016. A starfish robot based on soft and smart modular structure (SMS) actuated by SMA wires

Rincon. 2011. Starfish-inspired ‘soft’ robot squeezes under obstacles. https://www.bbc.co.uk/news/science-environment-15930007. Last accessed 13/05/2021

Poungrat and Maneewarn. 2017. A starfish inspired robot with multi-directional tube feet locomotion

Yang et al. 2021. Starfish Inspired Milli Soft Robot With Omnidirectional Adaptive Locomotion Ability

MIT Computer Science & Artificial Intelligence Lab. 2021. Robo-starfish aims to enable closer study of aquatic life. https://www.csail.mit.edu/news/robo-starfish-aims-enable-closer-study-aquatic-life. Last accessed 13/05/2021

Braun. 2018. Sea-Star Murdering Robots Are Deployed in the Great Barrier Reef. https://www.smithsonianmag.com/innovation/sea-star-murdering-robotsa-are-deployed-in-great-barrier-reef-180970177/#:~:text=The%20RangerBot%20is%20a%20new,smithsonianmag.com. Last accessed 13/05/2021

Espiner. 2015. Starfish-killing robot close to trials on Great Barrier Reef. https://www.bbc.co.uk/news/technology-34129490. Last accessed 13/05/2021

Image sources

Hans Hillewaert. 2000. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/)]. https://commons.wikimedia.org/wiki/File:Asterias_rubens.jpg

André-Philippe D. Picard. 2011. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:D%C3%A9tail_bras_d%27%C3%A9toile_de_mer.jpg

AlexEng. 2010. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Sunflower_Seastar.jpg

M.Buschmann. 2004. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Asterias_rubens_(eating).jpg

NOAA. 2006. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Starfish_eversion.jpg

Krzysztof A. Zacharski. 2017. [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]. https://commons.wikimedia.org/wiki/File:Mixed-culture_biofilm.jpg

NOAA Photo Library. 2013. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Crinoid_and_comatule.jpg

Miya. 2004. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Asterina_pectinifera_ja01.jpg

384. 2017. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Broken_starfish.jpg

All other images are public domain and do not require attribution.

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

Energy is a major currency in the natural world. Every living thing gets it by eating food, using sunlight to make sugars, or by exploiting some other natural resource. But to do anything productive, and that includes just being alive, one has to spend energy and a lot of it. This is especially true in the top predators, whose powerful hunting techniques usually incur such a high energy cost that it makes sense to maintain a budget and only unleash their full potential at the opportune moment. 

Crocodiles, such as the particularly impressive saltwater crocodile and Nile crocodile, are no exception. Though thoroughly lazy when bathing in the sun, as many reptiles are compelled to due to being cold blooded, they are not to be underestimated when they are on the hunt. As well as their formidable size and teeth, these crocs are also patient, often stalking their prey in murky water.  Once in range, the crocodile will lunge forward with incredible speed and strength. If done right, their target will have no idea what hit them until it’s too late.

But as I said before, these bursts of power come at a cost, not just in the energy required for these strikes, but also in the speed at which this energy is needed. In turn, this requires a change in how that energy is released in the cells that make up the crocodile’s muscles.

Under normal conditions, energy is stored in an animal’s body in the form of glucose sugars. The energy is then released by a process called aerobic respiration (with oxygen), which consists of a long series of chemical reactions that includes oxygen and a great deal of cellular trickery to squeeze every last piece of energy out of each molecule of glucose.

But when that same animal needs a lot of energy very quickly, which tends to happen when you are hunting down your food, or running for your life, the aerobic method is too slow to keep up with demand. In this situation, anaerobic respiration (without oxygen) is the preferable alternative as it releases energy far quicker, though at the cost of efficiency. This version of respiration also leads to the build up of a waste product called lactic acid.

The body of any animal can only tolerate so much excess lactic acid, but it’s in this inconvenient side effect that crocodiles have a surprising advantage. For they can tolerate incredibly high levels of the acid that would kill most other animals. Perhaps this allows them to throw extra power into their attacks, or perhaps this extra resistance is linked to other behaviours that require anaerobic respiration in some capacity.

Crocodiles would have little oxygen to spare while they are submerged in water and preparing for an attack. During this time, they can minimise their energy consumption to some extent, but there are still basic life functions that cannot be switched off. To keep their body ticking over, they have to resort to anaerobic respiration and then launch at their prey with a body already brimming with lactic acid. Depending on the size of their catch, they may also have to drag it back into the water and tenderise their meal into manageable chunks. With barely a chance to catch their breath. 

This double whammy of a high energy demand during their attacks and a low oxygen supply during their underwater stalking may go some way to explain why the lactic acid tolerance of crocodiles is so high. And with the toll it would take on their existing energy reserves, it’s no wonder they have such voracious appetites. 

The lives of animals are full of choices that are influenced by how best to spend their energy reserves and this can lead to behaviours that would otherwise seem odd. Predators can ignore food sources that are too difficult to crack and prey can choose to ignore the first whispers of danger rather than lose valuable feeding time over a false alarm. Sometimes, parents will even abandon, or consume their current batch of young in hope that their future offspring will prove to be a better investment. Just like any human entrepreneur, animals often have to take risks by making, or not making, an energy investment for a chance to reap the best rewards in life.

From a human perspective 

Crocodiles are formidable hunters and they have been known to attack humans from time to time. Saltwater crocodiles and Nile crocodiles have racked up the highest number of attacks, both fatal and non-fatal, worldwide with a total of 1,350 and 1,005 attacks over the last ten years respectively. This sounds horrific, but these numbers average out at just over 230 attacks per year for both species combined, for a planet with billions of people. Like with sharks, the chances of being attacked by a crocodile are extremely remote and can be reduced further with little more than common sense.  

But let us not forget that humans exploit crocodiles for their meat and skin, often in dedicated farms. From time to time, we also capture and relocate crocodiles to zoos, for research purposes and to move problematic individuals away from a populated area. 

Since it’s rare for crocodiles to be taken away without a fight, the risk to the humans involved is obvious. But as the croc itself struggles against the ropes and nets, they build up a lot of lactic acid in their blood and muscles. It attempts to restrain the animal drag on too long, this build up can surpass even their astronomical tolerance with the crocodile eventually struggling itself to death.  Sometimes, they may be captured alive only to succumb to the ordeal a short while later due to the oxygen not coming in fast enough to deal with the adverse effects on their body.

Thankfully, there have been attempts to develop new methods of capture that would make the whole experience less stressful for the crocodile. And probably less tense for their human captors as well.

A study published in 2003 trialed the use of ‘electrostunning’ on saltwater crocodiles (effectively applying a taser to the back of the neck). Compared to manual restraint alone (in this case noosing the animals with rope), the electrostunned crocodiles didn’t experience as much of a build up in lactic acid, or in other telltale chemicals in the blood. There was still a build up regardless of what method was used, as there would have been some maneuvering involved to get the crocs from the electrostunned group into position.

A later study applied a similar test, but on Nile crocodiles, stating outright that different crocodile species might react differently to electrostunning. In the end, they also concluded that electrostunning was better than manual restraint (albeit for different reasons) for welfare of the animals and the safety of their human handlers. In a dramatic twist, someone was actually bitten while grappling with one of these crocodiles from the manual restraint group.

Pitted against each other in a straightforward fight, a human being would not last long against a fully grown crocodile. But in the real world, our ingenuity has firmly shifted the balance in our favour thanks to a few millennia of technological advancements. So bolstered are we by boats, chemical formulas and electrical appliances that we don’t always need to kill everything in sight, even when they have powerful muscles and sharp teeth. A concept that would have seemed impossible to our caveman ancestors. 

Sources

Beatson. 2020. Estuarine Crocodile. https://australian.museum/learn/animals/reptiles/estuarine-crocodile/. Last accessed 24/02/2021

Crocodile Specialist Group. Respiration. http://www.iucncsg.org/pages/Respiration.html#:~:text=Crocodilians%20can%20struggle%20furiously%20when,the%20blood%2C%20making%20it%20acidic. Last accessed 01/04/2021

Britton. How fast can a crocodile run? http://crocodilian.com/cnhc/cbd-faq-q4.htm. Last accessed 14/03/2021

NHS Gloucestershire Hospitals. 2016. Lactate (Blood). https://www.gloshospitals.nhs.uk/our-services/services-we-offer/pathology/tests-and-investigations/lactate-blood/. Last accessed 22/02/2021

Khan Academy. Cellular respiration review. https://www.khanacademy.org/science/high-school-biology/hs-energy-and-transport/hs-cellular-respiration/a/hs-cellular-respiration-review. Last accessed 07/04/2021

BioNinja. Aerobic Overview. https://ib.bioninja.com.au/higher-level/topic-8-metabolism-cell/untitled/aerobic-overview.html. Last accessed 07/04/2021

https://www.livescience.com/lactic-acid.html#:~:text=Lactic%20acid%2C%20or%20lactate%2C%20is,muscle%20and%20red%20blood%20cells.

Bennett et al. 1985. Mass-Dependence of Anaerobic Metabolism and Acid-Base Disturbance During Activity in the Salt-Water Crocodile, Crocodylus Porosus

Seymour et al. 1985. Blood gas tensions and acid-base regulation in the salt-water crocodile, Crocodylus porosus, at rest and after exhaustive exercise

Noah C. 2020. HOW DO CROCODILES STAY SUBMERGED SO LONG? https://zooatlanta.org/how-do-crocodiles-stay-submerged-so-long/. Last accessed 14/03/2020

Summers. 2005. Warm-hearted crocs

Seymour et al. 2004. Evidence for endothermic ancestors of crocodiles at the stem of archosaur evolution

Viegas. 2008. Crocs divert blood to avoid busting a gut. https://www.abc.net.au/science/articles/2008/02/11/2159238.htm#:~:text=Since%20the%20large%20reptiles%20leap,that%20shoots%20to%20their%20stomachs. Last accessed 22/02/2021

Farmer et al. 2008. The right-to-left shunt of crocodilians serves digestion

Baldwin et al. 1995. Scaling of anaerobic metabolism during exercise in the estuarine crocodile (Crocodylus porosus)

Campbell et al. 2010. Ecological and physiological determinants of dive duration in the freshwater crocodile

Grigg. 1991. Central cardiovascular anatomy and function in Crocodilia

Owerkowicz and Baudinette. 2008. Exercise training enhances aerobic capacity in juvenile estuarine crocodiles (Crocodylus porosus)

Crocodile Specialist Group. Crocodilian Attacks. http://www.iucncsg.org/pages/Crocodilian-Attacks.html. Last accessed 25/04/2021

The State of Queensland, Department of Environment and Science. 2008. Code of Practice for the Taking, handling and transportation of crocodiles: Nature Conservation Act 1992. https://environment.des.qld.gov.au/__data/assets/pdf_file/0030/88590/cp-wl-croc-handling-transport.pdf 

Seymourl et al. 1987. Effect of Capture on the Physiology of Crocody lus porosus

Franklin et al. 2003. Comparison of stress induced by manual restraint and immobilisation in the estuarine crocodile, crocodylus porosus

Pfitzer. 2013. Physiological parameters of farmed Nile crocodiles (Crocodylus niloticus) captured manually and by electrical immobilisation

Olsson and Phalen. 2013. COMPARISON OF BIOCHEMICAL STRESS INDICATORS IN JUVENILE CAPTIVE ESTUARINE CROCODILES (CROCODYLUS POROSUS) FOLLOWING PHYSICAL RESTRAINT OR CHEMICAL RESTRAINT BY MIDAZOLAM INJECTION

Image sources

Gianfranco Gori. 2010 [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:NileCrocodile–Etiopia-Omo-River-Valley-01.jpg

Lip Kee from Singapore, Republic of Singapore. 2008. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Crocodile_attack_during_Mara_River_crossing_-_frame_1_-_Flickr_-_Lip_Kee.jpg

Boumphreyfr. 2009. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Aerobic_pathways.png

Lisawerner9. 2021. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Lactic_Acid_Fermentation.svg

Matt from Melbourne, Australia. 2009. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Saltwater_Crocodile_(Crocodylus_porosus)_(8851850268).jpg

Radhika Kochhar. 2012. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Crocodile_at_Ranganathittu,_Mysore,_Karnataka.JPG

Kerry Raymond. 2018 [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)]. https://commons.wikimedia.org/wiki/File:Crocodile_warning_sign,_Bramston_Beach,_2018.jpg

Alex Castro. 2010. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Crocodile_Warning_Dili.jpg

Kerry Raymond. 2016. [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)%5D . https://commons.wikimedia.org/wiki/File:Crocodile_warning_sign,_Slade_Point,_2016.jpg

Fritz Geller-Grimm. 2001. [CC BY-SA 2.5 (https://creativecommons.org/licenses/by-sa/2.5)]. https://commons.wikimedia.org/wiki/File:Krokodilmenu_fg1.jpg

User:Gisling. 2006. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Crocodile_wallets.jpg

MartinRe at the English-language Wikipedia. 2003. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Crocfarm.jpg

Zachi Evenor. 2017. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:Crocodylus-niloticus-Crocoloco-296-Zachi-Evenor.jpg

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

There is so much diversity in the oceans. A place where life has found millions of ways to live, build, fight and avoid dying for as long as possible. With so much out there, it’s inevitable that some species, or even groups of species, will be overlooked to the extent that we sometimes forget they exist at all. In my last article, I briefly mentioned how cuttlefish are sometimes overshadowed by their squid and octopus cousin. What I failed to mention is that there is a fourth group of cephalopod molluscs living in today’s oceans. The Nautiloids (also called Nautilus).

Nautiloids have been around for about 500 million years, long before the coeloids (the cephalopod sub-group that octopuses, squid and cuttlefish belong to) emerged. At the peak of their success, it is thought that there were around 2,500 different species of nautiloid. But over time, the world changed and new competition emerged. The mass extinction event at the end of the Cretaceous period (around 66 million years ago) was a particularly difficult time for the nautiloids. While whole animal groups were wiped out, the nautiloids pulled through, but never recaptured their former glory. Today, there are only six species left.

Nevertheless, nautiloids are still recognisable as cephalopods thanks to some tell tale features. They have strong tentacles, sharp beaks, well developed eyes and the ability to jump around by firing jets of water. But the one obvious feature they have which other living cephalopods don’t is a shell on the outside. External shells would have been a must have for all cephalopods at one time in earth’s history, but while the coeloids chose to abandon their shells, the nautiloids were more stubborn in the ways of their ancestors.

Even so, the nautiloid shell is an impressive feat of natural engineering, particularly on the inside where it is separated into a series of chambers The outermost chamber is huge and built for housing the animal itself, while all the others are built for holding gases and liquids to keep the nautiloid afloat. To allow them to float up and sink down as needed, the system is regulated by a tube called the siphuncle. This tube passes through each shell chamber, sucking up or dishing out gases and liquids.

The ocean is undoubtedly full of wonders. Some dominate this world as they have never done before while others belong to a world that faded away a long time. But that doesn’t mean these ‘living fossils’ have stopped evolving, only that they have chosen to refine existing designs rather than invent revolutionary new ones. Nautiloids have done this well enough to linger on while extinction has claimed so many others. But even for these survivors, the threats they face today are unprecedented, even for our planet. And it would be a terrible shame if we lost those last few links we have to the ancient seas.

From a human perspective

At the risk of contradicting what I was just saying about their obscurity, nautiloids have still managed to fascinate us from time to time. Their empty shells have long been moulded into jewelry and revered as natural curiosities while the very name Nautilus has inspired scientific journals, poems, science fiction aliens and Russian rock bands. In the novel Twenty thousand leagues under the sea, the Nautilus was the name of the vessel commanded by Captain Nemo as it travelled the oceans. A story that ended ironically (spoiler alert) with this particular nautilus being attacked by its most formidable cousin. A giant squid.

Returning to the real world, the ancient origins and design of nautiloids have made them very useful for understanding how life worked in the ocean long before we were around to take notes. We do also have the fossilised remains of sea creatures to work from, but often it’s only the hard shells and bones that come through the fossilisation process intact. We can work out a lot from these preserved hard parts, but we can also look to living surrogate species to fill in the blanks. In the case of those last few living nautiloids, they have been used as a surrogate species to study ammonites.

Ammonites were another group of cephalopods with outside shells who flourished at around the same time as the nautiloids. But while the nautiloids managed to just about hang on through the end of the Cretaceous period, the ammonites were completely wiped out. All we have left are the fossilised remains that have captured the attention of scientists for over 150 years. More than enough time and study to notice that the preserved shells of ammonites and the fresh shells of nautiloids are incredibly similar down to the way they’re divided into chambers on the inside.This strongly suggests that ammonites used the comparmentalised shells to float, just like our living nautiloids. 

But despite these similarities at face value, nautiloids are not a perfect match for ammonites. They’re not even their closest cousins with a series of subtle differences revealing that ammonites are more closely related to the coeloids (octopuses, squid etc.) than they are to nautiloids. One such subtle difference is in the design of the siphuncle, the tube that carries gas and liquid between shell chambers. In nautiloids, the tube is calcified (i.e. turned to bone) on the inside and soft on the inside, while in the ammonites and early coeloids (before they went shell-less) the tube is hardened inside and out. It’s a small modification, but it could have been what saved the nautiloids while the ammonites were going extinct.

Working out how prehistoric animals lived is always going to be a tricky business. The fossil record is patchy, the use of living surrogates is far from perfect and evolution does like to give us some bizarre twists along the way. It’s a testament to the skill and patience of paleontologists, and researchers in related fields, that we are not completely clueless about earth. Furthermore, we are forever discovering more fossils and developing new techniques to probe deeper into these fossils and into the lives they once lived. 

Sources

Wikipedia. 2020. Nautilus. https://en.wikipedia.org/wiki/Nautilus. Last accessed 06/01/2021

Wikipedia. 2021. Nautiloid. https://en.wikipedia.org/wiki/Nautiloid#:~:text=Nautiloids%20are%20a%20large%20and,the%20living%20Nautilus%20and%20Allonautilus. Last accessed 06/01/2021

Wikipedia. 2021. Coleoidea. https://en.wikipedia.org/wiki/Coleoidea. Last accessed 13/01/2021

Gross. 2015. Intelligent life without bones

Ward et al. 1980. The buoyancy of the chambered Nautilus

Vendetti. 2006. The Cephalopoda. https://ucmp.berkeley.edu/taxa/inverts/mollusca/cephalopoda.php. Last accessed 13/01/2021

Sedgwick Museum of Earth Sciences. Wenlock creatures: Nautiloids. http://www.sedgwickmuseum.org/index.php?page=nautiloids. Last accessed 06/01/2021

Denton and Gilping-Brown. 1966. On the buoyancy of the pearly Nautilus

NOAA. 2019. What is a nautilus? https://oceanservice.noaa.gov/facts/nautilus.html#:~:text=The%20tissue%20in%20a%20canal,backwards%20and%20to%20make%20turns. Last accessed 13/01/2021

Cleland. 2017. Nautilus cup. https://www.metmuseum.org/art/collection/search/193582. Last accessed 17/01/2021

The British Museum. Nautilus cup. http://wb.britishmuseum.org/MCN2585#1504261001. Last accessed 17/01/2021

ATG Reporter. 2017. ATG letter: Here’s why we shell out for carved nautilus. https://www.antiquestradegazette.com/print-edition/2017/june/2297/letters-to-the-editor/here-s-why-we-shell-out-for-carved-nautilus/. Last accessed 17/01/2021

Nautiloid,” 1A Collections, accessed January 13, 2021, https://wserv3.esc.cam.ac.uk/p1acollections/items/show/113.

Bailey-Matthews National Shell Museum. The Nautilus. https://www.shellmuseum.org/the-nautilus. Last accessed 13/01/2021

Encyclopædia Britannica. 2019. The Chambered Nautilus. https://www.britannica.com/topic/The-Chambered-Nautilus. Last accessed 13/01/2021

Dining with the Zarglorp. 2019. Archer. Series 10, episode 4. Written by Adam Reed and Shane Kosakowski. FXX. 19th June

Why Must I Be a Crustacean in Love? 2000. Futurama. Series 2, episode 9. Directed by Brian Sheesley and Bret Haaland. Written by Matt Groening, David X. Cohen and Eric Kaplan. Fox. 6th February

Meet Russia Online. 2019. Nautilus Pompilius – Russian rock born in USSR. https://meetrussia.online/nautilus-pompilius-russian-rock-born-in-ussr/. Last accessed 13/01/2021

British Geological Survey. Ammonites. https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/ammonites/. Last accessed 17/01/2021

Hall and Meek. 1855. Descriptions of New Species of Fossils from the Cretaceous Formations of Nebraska, with Observations upon Baculites ovatus and B. compressus, and the Progressive Development of the Septa in Baculites, Ammonites, and Scaphites

Jacobs and Landman. 1993. Nautilus—a poor model for the function and behavior of ammonoids?

Weaver. 2012. Cephalopod Awareness Days: Finally Some Fossils. https://naturalsciencesresearch.wordpress.com/2012/10/12/cephalopod-awareness-days-finally-some-fossils/. Last accessed 11/01/2021

Mutvei et al. 2007. Late Cambrian plectronocerid nautiloids and their role in cephalopod evolution

Kruta et al. 2011. The role of ammonites in the Mesozoic marine food web revealed by jaw preservation

Image sources

Profberger. 2007. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Nautilus_side.jpg

James St. John. 2016. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Nautilus_stenomphalus_(white-patch_nautilus)_(Mindanao,_Philippines)_2_(24078294661).jpg

Pujolle. 2007. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Nautilus_macromphalus_2b.jpg

Profberger. 2006. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Nautilus_profile.jpg

Teresa Martin. 2016. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Allonautilus_perforatus.jpg

Sérgio Valle Duarte. 2016. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:A_Nautilus_macromphalus_shell_inside.jpg

Philcha. 2009. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:Nautiloid_septa_n_siphuncle_01.png

Nobu Tamura (http://spinops.blogspot.com). 2009. [CC BY 3.0 (https://creativecommons.org/licenses/by/3.0)]. https://commons.wikimedia.org/wiki/File:Asteroceras_BW.jpg

LMCoelho. 2012. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Amonite-portugal.JPG

John Alan Elson. 2009. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Ammoniteplit.jpg

Kunstgewerbemuseum Berlin. 2011. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Berl%C3%ADn_KGM_nautilus.JPG

Ian Alexander. 2017. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Nautilus_shell_carved_and_painted_C19th_Poldi_Pezzoli_Museum.jpg

Ninjatacoshell. 2009. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Baculites_grandis_shell.JPG

Wilson44691. 2011. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)].  https://commons.wikimedia.org/wiki/File:BaculitidArticulated.jpg

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

Communication can be a tricky business in the sea. For many animals, it is impossible to complete their life cycle without sending and receiving messages with their own kind. But they often do so at the risk of giving away their position to their enemies. Sounds can be eavsedropped, odours and chemical trails can be followed with hungry noses and visual cues can be picked up by everyone in the local vicinity. It is a necessary risk, but it can also be managed by developing communication systems that are selective in who they talk to. 

Cuttlefish are a great example of this with their ability to change their appearance at a moment’s notice. They achieve this feat with chromatophores, specialised skins cells that can be stretched and relaxed to create changes in colour and contrast. Changing a single chromatophore sounds as simple as flicking a switch, but with the incredible cuttlefish brain they can coordinate millions of these switches at once. This system makes cuttlefish highly accomplished masters of disguise who can mimic and blend in with virtually any habitat. Not bad for a group of animals who are all colourblind and only have the contrasts between light and dark to work with. 

When cuttlefish want to make themselves seen, they can still use those same colour changing abilities, in combination with other visual cues such as moving their tentacles and adopting certain postures. The resulting colourful displays are often used to ‘talk’ to other cuttlefish (of the same species) during reproduction to indicate their gender, readiness to mate and to threaten romantic rivals. If they sense danger approaching, they can switch all their chromatophores to stealth mode and then pick up where they left off once they get the all clear. 

But the need to reproduce can make fools out of many animals, and cuttlefish are no exception. In the Australian giant cuttlefish, the possible fools are the large brutish males who honestly display their suitably as a mate and the superiority of their genes to seduce multiple females. The smaller males in the vicinity would not stand a chance against such fierce competition and so resort to sneakier tactics. Instead, they use their own colour shifting abilities to mimic the appearance of a female to deceive their way past another male and mate with his females when he’s not looking. 

For all their impressive abilities, cuttlefish are sometimes overlooked when compared to their squid and octopus cousins. The main distinguishing feature that cuttlefish possess is the cuttlebone, a shell they keep inside their body for controlling their buoyancy in the water. It may not sound like a particularly interesting namesake, but it is what makes cuttlefish unique among the cephalopods. And let us not forget that the evolution of the human race really got going with the simple breakthrough of opposable thumbs.

From a human perspective

Cuttlefish have proven to be a very useful natural resource for us and it appears that little is wasted from those we catch from the sea. For starters, we eat them in seafood dishes such as calamari and linguine where cuttlefish can be a cheap and tasty alternative to squid. This has proven to be popular in seafood cuisines in East Asia and the Mediterranean regions, but cuttlefish are also caught here in UK waters. But, as with any other seafood, it is important to buy and consume cuttlefish that have been caught sustainably with gear that causes minimal damage to the environment.

Throughout history we have also harvested cuttlefish for their ink to use in writing, drawing and painting. This practice is believed to date back to ancient Greece and Rome, but was probably at its most popular and refined during the 18th and 19th centuries. Only for cuttlefish ink to then become obsolete as alternatives were manufactured on an industrial scale. As for the ink itself, it typically produces a brownish colour with a hint of violet (though variations do exist) after it is extracted from the cuttlefish’s ink sac. The extraction process, depending on the exact method used, could involve drying the ink sack before subjecting the ink to a series of chemical treatments to make it more or less permanent. As demonstrated by some of the images below.

The previously mentioned cuttlebone has also proven to be a useful part of the cuttlefish anatomy with uses that include an ingredient in polishing powder and toothpaste, a strong mould in jewellery making and a possible use in producing building lime. Cuttlebone also has nutritional benefits due to it being rich in calcium and other minerals, and has been used as a food supplement for pet birds for over a hundred years.

Depending on the species of bird, the cuttlebone is simply hung in the cage for the bird to scrape and munch on, or it is ground into their food. The supposed health benefits include stronger bones, more effective blood clotting, a better immune system and so on. However beneficial a cuttlebone rich diet may be, there have clearly been financial incentives for supplying these supplements. During the research for this article I discovered a patent application (that was accepted) from 1885 for a new bird cage accessory for holding a piece of raw cuttlebone. 

Talking about the impact that marine animals have had on human culture and history can be a double edged sword. On the one hand, it is important to highlight just how connected we have always been with the oceans and appreciate what they have given us over the years. But this connection is often about us exploiting the natural world, sometimes stripping it bare when it suits us. But in the case of the cuttlefish, it is somewhat reassuring that we have found ways to use the less palatable parts of the animals rather than just throwing them away. If we are to use the oceans and its inhabitants for our benefit, we can at least do so  as sustainably and efficiently as possible.

Sources

Wikipedia. 2020. Cuttlefish. https://en.wikipedia.org/wiki/Cuttlefish. Last accessed 08/11/2020

Katcla. 2017. Fact Sheet: Cuttlefish. https://www.mba.ac.uk/fact-sheet-cuttlefish. Last accessed 14/11/2020

The Wildlife Trusts. Common cuttlefish. https://www.wildlifetrusts.org/wildlife-explorer/marine/squids-octopuses-and-cuttlefish/common-cuttlefish. Last accessed 14/11/2020

Hanlon. 2007. Cephalopod dynamic camouflage

Max Planck Society. 2018. Elucidating cuttlefish camouflage. https://phys.org/news/2018-10-elucidating-cuttlefish-camouflage.html. Last accessed 30/11/2020

Chiao and Hanlon. 2001. Cuttlefish camouflage: visual perception of size, contrast and number of white squares on artificial checkerboard substrata initiates disruptive coloration

Barbosa et al. 2008. Cuttlefish camouflage: the effects of substrate contrast and size in evoking uniform, mottle or disruptive body patterns

Hart. 2020. Cephalopods. https://acp.eugraph.com/cephal/#:~:text=Must%20be%20Jane.%E2%80%9D%20Cuttlefish%20and,gestures%20of%20their%20ten%20tentacles. Last accessed 04/12/2020

Zylinski et al. 2011. To Be Seen or to Hide: Visual Characteristics of Body Patterns for Camouflage and Communication in the Australian Giant Cuttlefish Sepia apama

Norman et al. 1999. Female impersonation as an alternative reproductive strategy in giant cuttlefish

Denton and Gilpin-Brown. 1959. Buoyancy of the cuttlefish

AskNatureTeam. 2016. Gas-holding structure aids buoyancy: Cuttlefish. https://asknature.org/strategy/gas-holding-structure-aids-buoyancy-2/. Last accessed 10/12/2020

Great British Chefs. How to cook cuttlefish. https://www.greatbritishchefs.com/how-to-cook/how-to-cook-cuttlefish. Last accessed 26/11/2020

Cornwall Good Seafoood Guide. Cuttlefish. https://www.cornwallgoodseafoodguide.org.uk/fish-guide/cuttlefish.php#:~:text=Cuttlefish%20are%20related%20to%20squid,and%20an%20alternative%20to%20calamari. Last accessed 13/12/2020

TheeLadyG. 2018. What is a Cuttlebone, Anyway?. https://www.fishlore.com/aquariumfishforum/resources/what-is-a-cuttlebone-anyway.99/. Last accessed 13/12/2020

Cadman et al. 2012. Cuttlebone: characterisation, application and development of biomimetic materials

惠友恒. 2013. CN104546623A – Cuttlebone-containing toothpaste. Google Patents. Patent no. CN104546623A

Ragan. 2018. How-To: Cuttlebone Casting. https://makezine.com/2012/03/16/how-to-cuttlebone-casting/. Last accessed 13/12/2020

Brepohl. Cuttlefish Casting Method. https://www.ganoksin.com/article/cuttlefish-casting-method/. Last accessed 13/12/2020

Ferraz et al. 2020. Exploring the potential of cuttlebone waste to produce building lime

Great Companions. 2020. The Benefits of Cuttlebone for Birds. https://www.greatcompanions.com/product/the-benefits-of-cuttlebone-for-birds/#:~:text=Cuttlebone%20is%20an%20important%20dietary,trace%20minerals%20for%20your%20bird. Last accessed 21/11/2020

Boerner. 1885. Means for attaching cuttle-bone to bird-cages. UNITED STATES PATENT FMCE. Patent no. US325313A

Pets at home. Vitakraft Cuttlebone Bird Treat 2 Pack. https://www.petsathome.com/shop/en/pets/vitakraft-cuttlebone-bird-treat-2-pack#. Last accessed 26/11/2020

Galal. 2019. THE EFFECT OF ADDING CUTTLEBONE MEAL ON THE PRODUCTIVE AND REPRODUCTIVE PERFORMANCE OF JAPANESE QUAIL.

Encyclopaedia Britannica. 1998. Sepia. https://www.britannica.com/art/sepia-drawing-medium. Last accessed 26/11/2020

Ana. 2019. Let’s Talk About Sepia Ink. https://www.wellappointeddesk.com/2019/07/lets-talk-about-sepia-ink/. Last accessed 26/11/2020

Image sources

Hans Hillewaert. 2008. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)]. https://commons.wikimedia.org/wiki/File:Sepia_officinalis_(aquarium).jpg

Tongjin. 2007. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Broadclub_cuttlefish_sipadan.jpg

Raul654. 2005. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Camouflage.jpg

Lakshmi Sawitri. 2013. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Camouflaged_cuttlefish_(10020603595).jpg

Thomas Schoch. 2006. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Sepia-camouflage.jpg

Sylke Rohrlach from Sydney. 2013. [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)]. https://commons.wikimedia.org/wiki/File:Giant_Cuttlefish-sepia_apama_(8643345101).jpg

Mariko GODA. 2012. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Cuttlefish-Cuttlebone2.jpg

SecretDisc. 2011. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:3D_visualisation_of_%C2%B5CT-data_of_a_cuttlebone_05.jpg

Pieter Bruegel the Elder. 1554 (uploaded to Wikimedia in 2020). CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Hilly_Landscape_with_a_Church_and_Watermill.jpg

David Adam Kess. 2012. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:A_black_and_white_photograph_Reina_Sofia_Museum_Madrid_Spain.jpeg

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram

by Matthew Norton

In a world with ocean giants such as sharks, dolphins and whales, it can be easy to forget about the smaller animals and how they play their own roles in the sea machine. Copepods, tiny crustaceans that can only reach lengths of 1-2 millimeters, are one such group of unsung heroes. What they lack in size, they more than make up for in sheer numbers, exceeding the head count of most, if not all animals on earth. Copepods are also found in almost any body of water and are an important food source for many animals. Often bridging the gap between phytoplankton (tiny aquatic plants) and the meat eaters.

But copepods are more than just a selection of light bites. One of their most impressive tricks is their ability to jump at speeds of 2-4 miles per hour to evade predators and move towards food. These speeds would be easy enough for large animals like ourselves, but if you scale it down to copepod size it would be the same as a human being reaching nearly 4,000 miles per hour in a single bound. These powerful jumps are made possible by their streamlined shape, quick reflexes and possession of two types of ‘swimming legs’. Those nearer the head are used for casual movement and feeding strategies that do not require fast jumps. The swimming legs further down the body are reserved entirely for those fast jumps and not tired out by other tasks before the copepod desperately needs them.

Such powerful jumps will inevitably leave vortex rings, spinning vacuums of water, in their wake which could leave a trail for their predators to follow. But copepods deliberately create two vortex rings per jump that spin in different directions. When combined, these vortex rings (almost) cancel each other out and cover the copepod’s tracks.

Unfortunately for our copepods, these fast jumps are mostly useless against seahorses and other predators that can approach undetected and strike with no warning. Ironically, it is the slow and gentle swimming of a seahorse, combined with their convincing camouflage, that makes them invisible to the copepods. Even their snouts are built to minimise the disturbances they cause in the water and allow the seahorse to get within striking distance.

Copepods, and their seahorse predators, are shining examples of what the littles guys and girls in the sea are capable of. If we could somehow take away the size difference, the copepods would likely outshine the ocean giants. Then again, it is just as likely that their small size is the key to their accomplishments. We all live in the same world, but the way it looks to a tiny copepod would be very different from our own experiences. A pond for example, is merely a small body of water with some interesting plants and animals for us. But to a copepod, that same pond is a vast wilderness full of dangerous beast and tempting riches. The rules they have to follow and the challenges they will face are completely different, but so are the opportunities.

From a human perspective

Not all copepods are fast jumpers. Many species have opted for a parasitic lifestyle and stay attached to a host animal for the whole of their adult lives. This can become a problem when they target marine animals that we want to eat. The aquaculture industry in particular have found copepod parasites like the dreaded ‘sea louse’ to be an expensive thorn in their side because no one wants to eat diseased fish.

Direct infection of human beings is unlikely, but copepods can act as unintended carriers (so far as we know) of human diseases that can be transmitted from drinking water, such as cholera and the guinea worm parasite. Wherever there is water, there are probably copepods to make it more difficult to eradicate these diseases. But the key role that they play in transmission could also help us to predict outbreaks and put measures in place to stem the tide of infections. One such early warning system could be to monitor the environment for explosions of phytoplankton growth (called blooms). With more food in the water, there are likely to be more copepods swimming around and therefore more potential carriers of disease. 

Copepods can also protect us from diseases that are spread by their prey. This applies to diseases spread by insects who spend part of their lives as aquatic larvae before morphing into their adult form and flying away. The more copepods there are in a given water body to pick off the insect larvae, the fewer carriers there are available to spread disease. Using copepods in this way has had some success in controlling the spread of dengue fever and could theoretically be used against other nasty tropical diseases. 

But we must be careful with manipulating nature to help control diseases, or we could end up getting carried away and making things worse. This was the case with the western mosquitofish (Gambusia affinis), a freshwater fish that was introduced in many countries in the early 20th century to combat the spread of malaria. As with copepods, this fish consumes insect larvae during their aquatic larval stage and using it’s natural feeding habits probably made perfect sense at the time. However, the western mosquitofish has outstayed its welcome and has been outcompeting native mosquito eating fish, species that could have done a better job of controlling the spread of malaria. I am not saying we shouldn’t ever make use of our natural resources, but in this kind of enterprise it would be wise to exercise some cautious doubt until we know the full implications of what we are doing.

Also, as helpful as copepods can be for dealing with obvious problems like disease, it is what they do in the background that is the most important and least appreciated. For example, their role in the global carbon cycle is substantial given that they are a major consumer of phytoplankton. Much of this carbon, which the phytoplankton originally extracted from the water as carbon dioxide, will travel up the food chain. But a portion will sink towards the bottom as uneaten copepod corpses and faeces. Given the rapid increases in carbon dioxide in the atmosphere, and dissolved in water, we should hope that the carbon filled remains of these copepods are locked away for a very long time.

Anyone reading this article might feel a bit uneasy about the idea of protecting our planet over protecting ourselves from disease, especially given our current circumstances. But disrupting the balance of nature will have far reaching consequences that include changes in how diseases operate and spread. The coronavirus pandemic may very well be the latest in a long line of high profile and disastrous consequences of our poor treatment of the natural world. Clearly something needs to change, but for truly effective conservation we have to show consideration to the whole environment and everything that lives within it. Even those tiny little copepods.

Sources

Wikipedia. 2020. Copepod. https://en.wikipedia.org/wiki/Copepod. Last accessed 23/09/2020

Boxshall and Defaye. 2008. Global diversity of copepods (Crustacea: Copepoda) in freshwater

Dürbaum & Thorsten-D. Künnemann. 2010. Biology of Copepods: An Introduction. https://web.archive.org/web/20100526164720/http://www.uni-oldenburg.de/zoomorphology/Biologyintro.html. Last accessed 11/10/2020

Krillson. 2018. Copepod Speed and Strength. https://copepods.com/blogs/copepods-com/copepod-speed-and-strength. Last accessed 13/10/2020

Choi. 2020. Flea-Sized Creatures Are Fastest Jumpers Known. https://www.livescience.com/8247-flea-sized-creatures-fastest-jumpers.html. Last accessed 13/10/2020

Tiselius et al. 2013. Sensory capabilities and food capture of two small copepods, Paracalanus parvus and Pseudocalanus sp

Kiørboe et al. 2010. Danger of zooplankton feeding: the fluid signal generated by ambush-feeding copepods

 Jiang and Kiørboe. 2011. Propulsion efficiency and imposed flow fields of a copepod jump

Technical University of Denmark (DTU). 2010. “What makes world’s strongest animal — the tiny copepod — so successful?. https://www.sciencedaily.com/releases/2010/05/100512172444.htm. Last accessed 11/10/2010

Kennedy. 2019. Special Feeding Adaptations of the Seahorse. https://www.thoughtco.com/what-do-seahorses-eat-2291410#:~:text=Seahorses%20do%20not%20have%20teeth,well%20adapted%20for%20catching%20prey. Last accessed 13/10/2020

Andrei. 2013. Seahorses are stealthy, efficient hunters. https://www.zmescience.com/science/biology/seahorses-snout-hunters-27112013/#:~:text=Seahorses%20are%20some%20of%20the,creep%20up%20on%20their%20prey. Last accessed 13/10/2020

Morgan. 2013. Seahorses stalk their prey by stealth. https://www.bbc.co.uk/news/science-environment-25103455. Last acessed 19/10/2020

Johnson et al. 2004. A review of the impact of parasitic copepods on marine aquaculture

Feis et al. 2019. Global invasion genetics of two parasitic copepods infecting marine bivalves

Natural History Museum. Copepod colonisation and parasitism. https://www.nhm.ac.uk/our-science/our-work/origins-evolution-and-futures/copepod-colonisation-parasitism.html. Last accessed 13/10/2020

Leitzell. 2011. The time of cholera. https://earthdata.nasa.gov/learn/sensing-our-planet/the-time-of-cholera. Last accessed 01/10/2020

Colwell and Huq. Cholera-Carrying Copepod. https://www.nsf.gov/news/speeches/colwell/rc01_anatlesson/tsld024.htm. Last accessed 01/10/2020

Huq et al. 1983. Ecological relationships between Vibrio cholerae and planktonic crustacean copepods.

Centers for Disease Control and Prevention. Parasites- Guinea Worm. https://www.cdc.gov/parasites/guineaworm/epi.html#:~:text=People%20become%20infected%20with%20Guinea,in%20these%20stagnant%20water%20sources. Last accessed 01/10/2020

Garrett et al. 2020. Dogs and the classic route of Guinea Worm transmission: an evaluation of copepod ingestion

Udayanga et al. 2019. Predatory efficacy of five locally available copepods on Aedes larvae under laboratory settings: An approach towards bio-control of dengue in Sri Lanka

Lazaro et al. 2015. Community effectiveness of copepods for dengue vector control: systematic review

CDC. 2018. Potential Range in US. https://www.cdc.gov/zika/vector/range.html. Last accessed 24/10/2020

CABI. 2010. Gambusia affinis (western mosquitofish). https://www.cabi.org/isc/datasheet/82079. Last accessed 24/10/2020

Global Invasive Species Database. 2010. Gambusia affinis. http://www.iucngisd.org/gisd/species.php?sc=126. Last accessed 24/10/2020

Yorukoglu. 2019. Copepods: The unsung heroes of the ocean. https://phys.org/news/2019-04-copepods-unsung-heroes-ocean.html. Last accessed 11/10/2020

Harvard T.H. Chan. Coronavirus and Climate Change. https://www.hsph.harvard.edu/c-change/subtopics/coronavirus-and-climate-change/#:~:text=Scientists%20are%20seeing%20an%20’acceleration,pathogens%20to%20find%20new%20hosts. Last accessed 06/11/2020

Image sources

Andrei Savitsky. 2019. [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:%D0%92%D0%B5%D1%81%D0%BB%D0%BE%D0%BD%D0%BE%D0%B3%D0%B8%D0%B5_%D1%80%D0%B0%D0%BA%D0%BE%D0%BE%D0%B1%D1%80%D0%B0%D0%B7%D0%BD%D1%8B%D0%B5_%D1%80%D0%B0%D0%B7%D0%BD%D1%8B%D1%85_%D0%B2%D0%B8%D0%B4%D0%BE%D0%B2.jpg

Uwe Kils. 2016. [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]. https://commons.wikimedia.org/wiki/File:Copepodkils.jpg

Florin DUMITRESCU. 2007. [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]. https://commons.wikimedia.org/wiki/File:Black_Sea_fauna_Seahorse.JPG

Hans Hillewaert. 2008. [CC BY-SA 4.0  (https://creativecommons.org/licenses/by-sa/4.0)]. https://commons.wikimedia.org/wiki/File:Acanthochondria_cornuta_on_flounder.jpg

Geoff Boxshall. 2012. [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]. https://commons.wikimedia.org/wiki/File:Lernaeolophus_sultanus_on_Pristipomoides_filamentosus_New_Caledonia.tif

Anwar Huq, University of Maryland Biotechnology Institute, Baltimore, Maryland, United States. 2003. [CC BY 2.5 (https://creativecommons.org/licenses/by/2.5)]. https://commons.wikimedia.org/wiki/File:Washing_Utensils_And_Vegetables.png

Muhammad Mahdi Karim. 2009. [GFDL 1.2 (http://www.gnu.org/licenses/old-licenses/fdl-1.2.html)]. https://commons.wikimedia.org/wiki/File:Aedes_aegypti_feeding.jpg

All other images are public domain and do not require attribution

For more bitesize content and ocean stories why not follow ‘Our world under the waves’ on…

🌊 Facebook 🌊 Bluesky 🌊 Instagram