Marine snow-Water wonderland

by Matthew Norton

The deep sea might look like a dark and desolate world but look closer and you will find that it is full of wonderfully weird creatures who have thrive in this environment despite the unique challenges they face. One particularly big problem is that there is not enough sunlight to support any plants, so the traditional food chain (plant → plant eater → animal eater) doesn’t work down there. Some species instead turn to alternative energy sources, such as the chemicals that leak out from hydrothermal vents and methane seeps, while others scavenge from the corpses of large animals. There is however a third option, which is to pick out the many smaller pieces of food that rain down from the surface as ‘marine snow’.

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Each of these ’snow’ particles are held together with extrapolymeric substances (EPS), a goo found the cells of most organisms (from large animals to microscopic bacteria) that can leak, especially when these cells start breaking down.

Each particle of marine snow is made from numerous dead or dying organisms (detritus is the technical term) stuck together along with other bits and pieces, such as sand, dust and animal faeces poo. These particles can provide temporary oases for living microorganisms such as bacteria and protists, who live in much greater densities on marine snow than in the surrounding water. It’s almost a shame that at any moment a slightly larger animal could come along and eat it, and it will likely happen because these particles are easy meals that can’t run, hide, or fight back (unless there are toxic or disease-causing microorganisms in the mix). Should they reach the seafloor uneaten, these particles may still get dug out of the sand, or mud and gobbled down by various bottom dwelling animals. Very little goes to waste in the marine environment.

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Krill (left) and the larvae of Japanese eels (right) are just two examples of small marine animals who benefit from having access to marine snow as a food source. There are probably many others that we don’t know about, especially in the ocean depths.

In theory, marine snow can be made of anything that was once alive in the sea, but there are some groups that make especially large contributions to making these particles. For example, phytoplankton leave behind large numbers of dead cells, especially in the aftermath of blooms (explosions in phytoplankton growth), along with the remains and faeces of animals that came to eat them. Larvaceans (tadpole-like animals) also leave behind ‘ready-made’ balls of marine snow when they dispose of their jelly-like ‘houses’. These houses, and all its inbuilt filters and funnels, are the key to their ability to filter out tiny pieces of food from the water, but they get clogged up very easily and the only solution is to get rid of them and start again. Still, this does leave behind plenty of food for other creatures in the water and a fair amount of slime to stick it all together.

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Part of a dead diatom cell surrounded by bacteria and other bits and pieces (left) and a larvacean (Oikopleura dioica) who has to abandon their clogged up house every few hours (right). Both scenarios are ideal for creating marine snow.

With so much marine snow raining down from the ocean surface it seems almost inevitable that some of it will reach the deepest parts of the ocean, but that doesn’t mean that those sunlit waters get nothing in return. Some of the oxygen and nutrients that build up in the deep sea (fewer animals down there to use them) is eventually carried back up to the surface by ocean currents in a process called upwelling. In some coastal regions, this process can provide the ideal conditions for the growth of the very phytoplankton that plays such a big role in creating marine snow in the first place. The ocean surface and deep sea are two very different worlds, but there is still a connection between them.

From a human perspective

The idea that food rains down from the ocean surface has persisted almost as long as we have known that there was life down in the deep sea. As far as we know, the phenomenon was first suggested during the 1872-1876 voyage of the HMS Challenger which, like several voyages on other ships, recovered specimens from the deep sea by using a dredge attached to a very long steel cable. Apparently, at some point during the voyage someone suggested that those creatures survived, despite being isolated from the sun, by feeding on a ‘rain of detritus’ from the surface.

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During its long voyage, the HMS Challenger collected a considerable amount of scientific data from the ocean which ranged from measuring environmental conditions (e.g. temperature, depth, salinity) as well as dredging the seafloor at various depths to collect samples and living specimens. The use of long cables made of steel made it possible to reach the dark depths and bring back its weird creatures.

However, no one actually saw this until William Beebe, an American naturalist and explorer (among other things), conducted a number of deep sea dives in the 1930s. He achieved this feat in a vehicle called the ‘bathysphere’, a diving bell suspended from a steel cable attached to a ‘mother’ ship (pretty basic, but you’ve got to start somewhere). From the porthole windows of the bathysphere, Beebe could see and identify various animals as they swam past and crucially, he could see those strange particles of which he called marine snow. It’s hard to imagine what that experience must have been like, to see the underwater world at such depths and relatively unaffected by humanity. This is a privilege that is becoming increasingly rare in the modern world.

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William Beebe’s bathysphere suspended from its steel cable (left) and at its current home at the National Geographic museum in Washington DC (right). I would also recommend looking up the article that Beebe wrote for the National Geographic Society in exchange for funding his dives.

William Beebe was unlikely to see any plastic rubbish during his dives in the bathysphere, but now it is one of the biggest threats to marine animals in every corner of the ocean. Many animals get caught up in bags, discarded fishing lines and other plastic rubbish, and suffering deep cuts and broken bones from trying to break free and if they don’t succeed, they will either drown or starve. Some animals will also eat plastic (mistaking it for prey), which then gets stuck inside their stomach and leaves less room for real food. Often, the victim doesn’t realise they are starving because they still get that feeling of being full from all the plastic in their stomach as they waste away.

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These are just a few examples of how plastic pollution is impacting our oceans. Abandoned fishing nets (left) which can be dragged by ocean currents and trap any creatures caught in its path, plastic bags (centre) which can be mistaken for food and eaten by certain sea creatures and microplastics (right) which can be eaten by tiny creatures and then move up the food chain and accumulate in large predators.

Even the deep sea is not safe with records of plastic rubbish along the seafloor and right down to the Mariana Trench as well as plastic being recovered from the guts of various animals including deep sea fish, lobsters, anemones and sea cucumbers. We can only hope that some of this rubbish gets buried so far down in the seafloor that it stays out of the reach of any living creature, human or otherwise. Who knows, in the far future these plastics may be discovered among the fossilised remains of animals who are alive today. Hopefully, such reminders of how reckless we used to be with the natural world will be rare.

Plastic pollution is a serious issue that requires urgent action and the deep sea is no exception. Frankly, this has been known for a long time, but the scientific evidence can easily go under the radar unless it is made accessible and communicated in a way that actually inspires people to take notice and do something about it. For example, there have been scientific papers about plastic pollution for decades and the threat of microplastics has been covered in the literature since at least 2004. The existence of rubbish in the sea was even casually depicted in a classic Tom and Jerry film from 1947 called “Saltwater Tabby” where Tom (the cat) is at the beach and accidently dives into a pile of rubbish that was hidden by the sea until the last second. Despite all this, the issue only got the worldwide attention it really needed when David Attenborough raised awareness of it in “Blue Planet 2”, which just goes to show that communication and reaching out to people is key to protecting the natural world.

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Thanks for reading


NOAA. 2018. What is marine snow?

Wikipedia. 2020a.

Lampitt et al. 1993. Marine snow studies in the Northeast Atlantic Ocean: distribution, composition and role as a food source for migrating plankton

Dilling et al. 1998. Feeding by the euphausiid Euphausia pacifica and the copepod Calanus pacificus on marine snow

Miller et al. 2013. A low trophic position of Japanese eel larvae indicates feeding on marine snow

Shanks and Walters. 1995. Feeding by a heterotrophic dinoflagellate (Noctiluca scintillans) in marine snow

Azam and Long. 2001. Sea snow microcosms

Wotton, R.S., 2004. The essential role of exopolymers (EPS) in aquatic systems

Eenennaam et al. 2016. Oil spill dispersants induce formation of marine snow by phytoplankton-associated bacteria

Alldredge and Gotschalk. 1988. In situ settling behavior of marine snow

Alldredge and Silver. 1988. Characteristics, dynamics and significance of marine snow

Lyons et al. 2005. Lethal marine snow: pathogen of bivalve mollusc concealed in marine aggregates

Simon et al. 1990. Bacterial carbon dynamics on marine snow

Silver. 2015. Marine Snow: A Brief Historical Sketch

Wikipedia. 2020b.

Rudd. 2014.

Wikipedia. 2020c.

NOAA. 2019.

IUCN. 2020.

Chiba et al. 2018. Human footprint in the abyss: 30 year records of deepsea plastic debris

Anastasopoulou et al. 2013. Plastic debris ingested by deep-water fish of the Ionian Sea (Eastern Mediterranean)

Taylor et al. 2016. Plastic microfibre ingestion by deep-sea organisms

Turner. 2002. Zooplankton fecal pellets, marine snow and sinking phytoplankton blooms

Cundell. 1974. Plastics in the marine environment

Thompson et al. 2004. Lost at sea: where is all the plastic?

Imdb. 2020.

Image sources

Russell R. Hopcroft, Institute of Marine Science, University of Alaska Fairbanks. 2005. [CC BY-SA (].

opencage. (unknown date). [CC BY-SA (].

Leo Wehrli. 1934. [CC BY-SA (].

Mike Cole. 2009. [CC BY (].

U+1F360. 2018. [CC BY-SA (].

Clandon haverford. 2018. [CC BY-SA (].

All other images are in the public domain and do not require attribution

Bryozoans-Welcome to the colony

by Matthew Norton

Most of the time, natural selection is focused on how the individual can survive and reproduce, but not everyone can do it on their own. Some creatures are so dependent on other members of their species that they stick together, making it hard to work out where one individual ends and the next one begins.

Bryozoans are one such group of invertebrate animals that live together in colonies (with one exception). Each animal is joined together with its next-door neighbours with a series of tubes that carry resources, such as food, throughout the colony. These connections run so deep that each ‘individual’ animal is called a zooid because they are not independent enough to be recognised as individual animals. Bryozoans would probably find this insulting if they ever found out how we talk about them, but their lack of individuality does allow them to share the workload with each zooid playing its own role to keep the colony alive.

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Some examples of bryozoan species with the seaweed shaped hornwrack (left) and sea mats growing on real seaweed (right). If you look really close, you can see each zooid in the bryozoan colony as a little ‘box’.

The most immediate concern for colony would be food with many zooids equipped with a feeding organ called a lophophore, a crown of hairy tentacles that catch small pieces of food from the water and flick them towards the mouth. However, with so many lophophores in such a small space these feeding zooids can easily get in each other’s way. The colony also has other needs for which a lophophore would be useless, so some of the zooids have replaced it with another tool.

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You can see from this photo how close each bryozoan is to each other with their lophophores sticking out.

For defending the colony from predators or rival colonies, some of the bryozoan zooids have spines or a set of snapping jaws (some say they look like mouse traps). Some species go even further with zooid types that are built for holding up the colony, protecting fertilised eggs and sweeping away pests (algae, tiny animals etc) with bristles. Incidentally, these bristles can also be used for ‘walking’ and digging the colony out of sand, a useful trick in busy areas where the sand is thrown around by ocean currents and other sea creatures.

There is just as much diversity between species with bryozoans being one of the most varied animal groups I have seen, and the image below shows this better than I could do with a thousand words. The only thing I will add is that colonies can vary in shape and size from sheets growing on plants and animals to ‘free living’ forms that look like seaweeds, corals and other creatures.

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These bryozoans were drawn by the naturalist Ernst Haeckel and it’s not the first time I’ve used his illustrations on my blog. They are beautifully detailed and coloured (it also helps that he has been dead long enough for the copyright to expire).

In reality, no one on this planet is truly alone. Every single plant, animal and human being on the planet is made up of millions of cells working in harmony to keep the body alive, most of the time. Even the single celled microorganisms such as bacteria and viruses are often sharing the air and water with millions, if not trillions of other microorganisms. Bryozoans are just a useful reminder of this universal fact.

From a human perspective

From time to time, we probably wish that we could live in a separate existence to the rest of life on earth (I suspect the feeling is mutual). No one likes catching a disease, being swarmed by flies, or being bitten by a wild beast. Bryozoans can also cause us a few problems.

Some of us, particularly fishermen and anyone handling their nets, have encountered the sea chervil (Alcyonidium diaphanum). This species of bryozoan is notorious for causing a skin condition called “Dogger Bank Itch” with symptoms including rashes and dermatitis which can be very uncomfortable in severe cases. Records of the condition in the North Sea date back to at least the 1930s, but it seems to have spread in recent years with recorded cases in Cornwall and the English Channel since 2000.

Other species can be a nuisance without coming anywhere near us. Similar to many other marine invertebrates, bryozoans can stick to our pipes, filters and any other hard surface we build in the water. This can lead to a messy situation when we need these pipes and filters to deliver clean drinking water and treat sewage, it’s bad enough when it’s our own crap causing these blockages (literally in some cases). Their tendency to stick to other sea creatures is also annoying if we are trying to farm them for food. Would you eat mussels in a restaurant if they were covered in weird squishy things?

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These zebra mussels really do not look appetising with all those bryozoans growing on their shells.

Bryozoans can cause another problem for fish farms by helping diseases to spread and kill off their fish. There is a particularly serious, and costly disease affecting salmon farms called “Proliferative kidney disease” with symptoms including swelling of the kidneys, abdomen and damage to other body organs. The culprit is a myxozoan (jellyfish-like) parasite, but they can’t spread directly from fish to fish and so need a middleman to piggyback off, with bryozoans being the prime suspect

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Proliferative kidney disease can affect wild salmon, but salmon in fish farms, such as the one above, are more vulnerable because it is easier for diseases to spread in confined spaces.

Despite all this negativity there is one species of bryozoan who could bring us some very good fortune. Bugula neritina, also known as brown bryozoans and common bugulas, produce chemicals called “bryostatins” which could be used to treat cancer and Alzheimer’s disease. I am saying “could” a lot because despite some promising results, this area of research is relatively young, and some clinical trials have raised doubts about their effects against certain types of cancer. An even bigger problem is how can we possibly meet the demand for bryostatins from this one species. A promising solution to this supply problem would be to develop synthetic copies that work just like bryostatins and can be easily mass produced, but this research is still ongoing.

Bringing humans and nature together can be a complicated business with interactions sometimes being unpredictable and dependent on the circumstances. Sometimes the benefits and drawbacks of such interactions are only realised after years of research, which is why it is important for humanity to do these scientific experiments, even some of the really wacky ones (within reason). In the case of bryozoans, we have been studying them for so long that I would have been surprised if we hadn’t found something useful from them by now. Imagine what else we might find in the near future.

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Thanks for reading


Wikipedia. 2019.

Riisgard and Manriquez. 1997. Filter-feeding in fifteen marine ectoprocts (Bryozoa): particle capture and water pumping

Grunbaum. 1995. A model of feeding currents in encrusting bryozoans shows interference between zooids within a colony

Okamura. 1987. Particle size and flow velocity induce an inferred switch in bryozoan suspension-feeding behavior

Carter et al. 2010. Polymorphism and vestigiality: comparative anatomy and morphology of bryozoan avicularia

Harvell. 1984. Predator-induced defense in a marine bryozoan

Banta. 1972. The body wall of cheilostome Bryozoa, V. Frontal budding in Schizoporella unicornis floridana

Winston. 1986. Victims of avicularia

Bradstock and Gordon. 1983. Coral‐like bryozoan growths in Tasman Bay, and their protection to conserve commercial fish stocks

Rogick. 1945. Studies on marine Bryozoa. I. Aeverrillia setigera (Hincks) 1887

Dea. 2009. Relation of form to life habit in free-living cupuladriid bryozoans


Newhouse. 1966. Dogger Bank itch: survey of trawlermen

Pathmanaban et al. 2005. Dogger Bank itch in the eastern English Channel: a newly described geographical distribution of an old problem

Wood and Marsh. 1999. Biofouling of wastewater treatment plants by the freshwater bryozoan, Plumatella vaihiriae (Hastings, 1929)

Mant et al. 2011. Biofouling by bryozoans, Cordylophora and sponges in UK water treatment works

Woods et al. 2012. Biofouling on Greenshell™ mussel (Perna canaliculus) farms: a preliminary assessment and potential implications for sustainable aquaculture practices

Scottish Government. 2013.

Centre for Environment Fisheries and Aquaculture Science. 2019.

Wahli et al. 2002. Proliferative kidney disease in Switzerland: current state of knowledge

Okamura and Wood. 2002. Bryozoans as hosts for Tetracapsula bryosalmonae, the PKX organism

Zonder et al. 2001. A phase II trial of bryostatin 1 in the treatment of metastatic colorectal cancer

Kollar et al. 2014. Marine natural products: bryostatins in preclinical and clinical studies

Ruan and Zhu. 2012. The chemistry and biology of the bryostatins: potential PKC inhibitors in clinical development

Image sources

Hans Hillewaert. 2007. [CC BY-SA 4.0].

Seascapeza. 2006. [CC BY-SA 3.0].

Lamiot. 2016. [CC BY-SA 4.0].

Richard Dorrell / Loch Ainort fish farm. 2011. [CC BY-SA 2.0].

All other images are public domain and do not require attribution

Bottlenose dolphins-The big boys club

by Matthew Norton

The open ocean offers a whole world to explore, provided you belong to a species of strong swimmers. There is however, a big difference between swimming to a new place and surviving there, which is why you can find big differences between groups of animals who live in different environments, even though they belong to the same species.

The bottlenose dolphin is one such species that has populations living all over the world with dramatic differences in body size. In Florida they reach a length of 2.5m which is rather unimpressive compared to world’s largest bottlenose dolphins, which can be found in the Moray Firth in Scotland and reach lengths of almost 4m. These Scottish dolphins are so big because it’s much colder in Scotland (I’ve noticed) and by having a larger body they can hold a thicker layer of fat under their skin (blubber) to keep themselves warm. It is also worth noting that they can throw their weight around while attacking porpoises and other dolphins. It is very unlikely that you would be attacked by a wild dolphin, but best not to make them angry.

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It is remarkable to think that bottlenose dolphins from the Moray Firth (left) can grow so big. It’s hard not to feel sorry for the harbour porpoise that they attack (right).

These big bottlenose dolphins need lots of food to sustain their body size, so it’s a good thing they are such effective hunters with their ability to use sound to find fish (echolocation) and sharp pointy teeth for catching them. They are also ‘opportunistic feeders’ which means if it’s fishy and they can catch it, they will eat it, but at the same time they are strategic with their feeding habits. In the Moray Firth you have a better chance of seeing bottlenose dolphin from the shore during the summer because they are hunting fish that come close to the shore, such as salmon swimming up and down the rivers. In the winter, they spend more time hunting other species of fish that gather in deeper waters, such as mackerel.

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The diet of a bottlenose dolphin includes (from the top) salmon, cod, haddock, herring, mackerel, sardines and more.

Moray Firth bottlenose dolphins are also opportunistic in the sense that they are still exploring with members of this population having been spotted further down the east coast in places like Aberdeen, St. Andrews and even northeast England, I hear Scarborough is especially popular. More recently dolphins from the Moray Firth have been spotted even further away in the Netherlands and around the coasts of Ireland. We know these dolphins came from the Moray Firth because we can track individual dolphins using photos of their dorsal fin which has a pattern of scratches, cuts and other markings that is unique to each dolphin (sort of like a fingerprint).

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Most of the (roughly) 200 bottlenose dolphins that live in the Moray Firth stay in this area all year round, as far as we know.

At the moment I don’t think anyone knows for sure (as of October 2019) why bottlenose dolphins are leaving the Moray Firth, but allow me to speculate on some possibilities. They may be struggling to find food in the Moray Firth and have gone looking for new feeding grounds. They may be trying to avoid inbreeding, which can cause all kinds of problems, by looking for other bottlenose dolphins to reproduce with. It is also possible that the environment is changing in the Moray Firth and is slowly driving them away, those who have already left may be ahead of the curve. I hope this isn’t the case; I have met many people in Scotland who are delighted to have these dolphins around.

Bottlenose dolphins are often described as being very intelligent animals, which is amazing, but this makes it more difficult to work out what they are doing and why. Maybe there is a perfectly logical reason why they explore, or don’t explore, the oceans of the world, but it is possible that they do it because they can.

From a human perspective

Watching whales, dolphins and porpoises in their natural habitat is one of the best life experiences you could wish for and Scotland is a great place to do it. As well as bottlenose dolphins, the Moray Firth is home to harbour porpoises and minke whales regularly visit during the summer, while along the Scottish coastline you can see over 20 different species including common dolphins, risso’s dolphins and orcas.

At Spey Bay (on the coast of the Moray Firth) you will also find the Scottish Dolphin Centre, which is run by a global charity called Whale and Dolphin Conservation (WDC) that is really pushing for the protection of whales and dolphins (and porpoises). I know the centre and WDC very well because for the last 8 months I have volunteered there as a residential guide and education volunteer (I should make it clear that they did not ask me to write and all opinions in this article are my own). This role was split between working ‘front of house’, running the shop and exhibition area, delivering tours and talking to people about whales and dolphins and WDC, and helping with the education programme, which involved running school activities, delivering community talks and planning holiday club activities. That last one was particularly fun because I had a lot of creative freedom, but there was the risk of all hell breaking loose, especially when water pistols were involved.

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The Scottish Dolphin Centre is the public face of Whale and Dolphin Conservation where we can talk to people face to face on a day to day basis about whales and dolphins and the work that WDC is doing to protect them. It adds an extra layer of engagement that is not so easy when you’re just working from the office. The café and their delicious cakes is also a significant bonus.

The Scottish Dolphin Centre was set up long before I came along, but I would still say that it breathed new life into the area and has raised awareness of the heritage and the local wildlife (other than dolphins). The centre itself was once a salmon fishing station that processed the fish caught in the river and sea. There is also an icehouse on site, the largest still standing in Scotland, for storing ice that was packed with the fish to keep them fresh at market. Today the icehouse is used as another exhibition area with immersive video rooms, old fishing and ship building tools and a room full of impressive whale and dolphin bones.

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The icehouse (left) was part of a massive fishing operation with thousands of salmon caught a day at its peak. This all ended in the 1990’s, but the river is still a beautiful place to visit and the fish (that survived us) bring dolphins, seals, otters and ospreys every year.

Reading through this article you are probably thinking that I am biased in favour of the Scottish Dolphin Centre and WDC, and you are probably right. So in the interest of balance I will admit that not every visitor was as impressed as I was when I first walked through those doors, but is a common fact of life that you cannot please everyone. In particular, some people were disappointed that they were not guaranteed to see bottlenose dolphins during their visit. However, all wild animals are unpredictable and WDC is firmly against keeping whales and dolphins in captivity. Besides, there are few things more special than that chance to see them in the wild where they belong.

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Thanks for reading


Wikipedia. 2019. Common bottlenose dolphin. Last accessed 05/11/2019

Whale and Dolphin Conservation. 2019. Common bottlenose dolphin. Last accessed 05/11/2019

Connor et al. 2000. THE BOTTLENOSE DOLPHIN: Social Relationships in a Fission-Fusion Society; Cetacean Societies: Field Studies of Dolphins and Whales. ISBN 9780226503417

Connor et al. 2004. Aggression in bottlenose dolphins: evidence for sexual coercion, male-male competition, and female tolerance through analysis of tooth-rake marks and behaviour

Parsons et al. 2003. Male-male aggression renders bottlenose dolphin (Tursiops truncatus) unconscious

Ross and Wilson. 1996. Violent interactions between bottlenose dolphins and harbour porpoises

Santos et al. 2001. Stomach contents of bottlenose dolphins (Tursiops truncatus) in Scottish waters

Hastie et al. 2004. Functional mechanisms underlying cetacean distribution patterns: hotspots for bottlenose dolphins are linked to foraging

Patterson et al. 1998. Evidence for infanticide in bottlenose dolphins: an explanation for violent interactions with harbour porpoises?

Ross Shire Journal. 2019. Moray Firth bottlenose dolphin Spirtle surprises experts after being spotted off south-west Ireland. Last accessed 05/11/2019

Evening express. 2019. Moray Firth dolphins spotted in Netherlands and Ireland. Last accessed 05/11/2019

Scottish Dolphin Centre. 2019. Last accessed 05/11/2019

Image sources

Shirehorse. 2007. [CC BY-SA 3.0 (

Hogweard. 2012. [CC BY 3.0 (

All other images are public domain and do not require attribution

Chinese mitten crabs-Long distance crawling

by Matthew Norton

Most living creatures have to be able to move at some point during their lives, to get food, to escape predators or to find new places to live. Some species take this one step further and live their lives while constantly on the move, such as the Chinese mitten crab. These little critters will travel over 1,000km upriver from their birthplace in the sea and then come all the way back down again to make their own baby crabs who will repeat this long voyage.

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Chinese mitten crab is a fitting name for these little critters given that they are native to China and have very hairy claws.

As tiny floating larvae, these little crabs cannot swim very far, but can still make their way from the coastal seas where they hatched from and into the estuary (the space between the sea and the rivers) by using the tides. The movement of the tides is strongest at the water’s surface and then gets weaker as you go down and the crab larvae take advantage of this by swimming up when the tide is coming in and then swimming down when the tide goes out. The result is that they get themselves pushed more by the incoming tide, which takes them further inland.

Manipulating the tides to propel yourself up rivers only works when the incoming tides can push against the river flow. After this point, crawling on the bottom of the river becomes a much easier way for Chinese mitten crabs to travel. Even so, they may still have hundreds of kilometres to go, but it can take them up to five years to be ready to travel back down and breed. At least they have time on their side.

On their travels, these little crabs will also have to cope with the challenges of moving between different environments. The change in salinity (saltiness of the water) they experience as they move from the sea to the river is particularly tricky to get around. All animals need a certain amount of salt in their bodies dissolved in a certain amount of water, too much salt or too little water and their cells will shrivel up, too much water or too little salt and their cells will get bloated and burst, neither are good outcomes. Aquatic animals use various methods to control the levels of salt and water in their bodies, such as moving salts over their gills, drinking, or not drinking water and using dissolved, non-salt chemicals to make up for a low salt content.

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These diagrams show how fish from freshwater (left) and seawater (right) regulate the levels of water and salt ions in their body. Both use very similar mechanisms, but in very different ways because for freshwater fish there is the risk of getting too much water and not enough salts whereas in seawater fish it is the other way round.

Regulating salt and water levels in your body is easy enough when the salinity of your environment doesn’t change much, but for Chinese mitten crabs a change in tactics is necessary when they move from sea to river and vice versa. As larvae, they are very skillful at cope with a wide range of salinities, but as they grow and move towards the river, where salinity is low, but stable, this becomes an unnecessary expense. This is probably why adult Chinese mitten crabs are not so flexible with salinity, at least until they return to the sea.

It does seem strange that these little make such long and difficult journeys, why not just stay in the sea close to where they were born. They may find more food, fewer predators or fewer competitors in the rivers, but their eggs and larvae may have a better chance in the sea, but this is just one of many possible reasons. Chinese mitten crabs are not the only species who seem to live a difficult life, but this can be necessary for them to live in a natural world where the ‘easy’ roles are already taken.

From a human perspective

Humanity has caused some significant damage to the natural world over the past few decades through global warming, pollution, invasive species and so on. That last one has certainly come back to haunt us in some parts of the world. In theory any species can become invasive if it makes it way to a new area by clinging to our boats, our floating rubbish, or if it is driven there by climate change. Once the species arrives and gets a foothold, it can play havoc with the local ecosystem, driving out species that actually belong there by hunting them, depriving their food or modifying the environment.

Chinese mitten crabs are one such invasive species who have spread through Europe and America since the start of the 20th century and they have made their presence known. There is evidence to suggest that they will forcibly evict shore crabs (Carcinus maenas) from their shelters on the shore, which is ironic given that they are an invasive species themselves in other parts of the world. They can also carry pathogens (disease causing microorganisms) which are deadly to native species, such as the fatal crayfish plague caused by the bacteria Aphanomyces astaci. Unfortunately, by the time we found out that Chinese mitten crabs were a carrier they had already occupied much of Europe.

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For European crayfish, Chinese mitten crabs are a significant threat, not only through competition for food and other resources, but also because they carry deadly diseases which crayfish have no resistance to.

There are problems for us as well, Chinese mitten crabs have a tendency to burrow into river banks, which can damage crops and destabilise anything we build close to the river, and interfere with fishing activities. Their larvae can also clog up our water pipes. However, some entrepreneurs have suggested turning the presence of these destructive crabs to our advantage, by harvesting and eating them. This has already been done in their native China, where they are farmed and ultimately served in seafood restaurants, and has been proposed in America and around the river Thames.

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Chinese mitten crabs are already farmed, harvested and cooked in China so it is possible to eat them in regions where they are an invasive species and get their populations under control at the same time.

Properly managed, this could be an ideal solution for keeping numbers of Chinese mitten crabs under control. However, there is a risk that profit may take priority over protecting native species and habitats and this could mean crabs being deliberately imported and farmed in areas where they don’t belong. Clearly, I am not the only one who is concerned because in most of the United States it is illegal to import and farm Chinese mitten crabs with the only exception being California, where some fishing is allowed.

There has been a lot of doom and gloom in this article, but at least we are coming up with solutions to the problems we are causing to the natural world. Some of these solutions, such as harvesting and eating Chinese mitten crabs, are particularly attractive because we can also make money from them. This can be a cause for concern, but I am still optimistic that we can still protect the underwater habitats we share with the natural world, so long as we don’t get carried away.

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Thanks for reading


Tilburg et al. 2011. Transport and retention of the mitten crab (Eriocheir sinensis) in a Mid-Atlantic estuary: predictions from a larval transport model

Veldhuizen. 2001. Life history, distribution, and impacts of the Chinese mitten crab, Eriocheir sinensis

Anger. 1991. Effects of temperature and salinity on the larval development of the Chinese mitten crab Eriocheir sinensis(Decapoda: Grapsidae).

Cohen and Carlton. 1997. Transoceanic transport mechanisms: introduction of the Chinese mitten crab, Eriocheir sinensis, to California

Wang. 2012. Characterization and expression of glutamate dehydrogenase in response to acute salinity stress in the Chinese mitten crab, Eriocheir sinensis

Inside Ecology. 2017. Invasive non-native species (UK) – Chinese mitten crab. Last accessed 26/08/2019

Dittel and Epifanio. 2009. Invasion biology of the Chinese mitten crab Eriochier sinensis: A brief review

Herborg et al. 2003. Spread of the Chinese mitten crab (Eriocheir sinensis H. Milne Edwards) in Continental Europe: analysis of a historical data set

Clark et al. 1998. The alien Chinese mitten crab, Eriocheir sinensis (Crustacea: Decapoda: Brachyura), in the Thames catchment

Rudnick et al. 2005. A life history model for the San Francisco Estuary population of the Chinese mitten crab, Eriocheir sinensis (Decapoda: Grapsoidea)

Schrimpf et al. 2014. Invasive Chinese mitten crab (Eriocheir sinensis) transmits crayfish plague pathogen (Aphanomyces astaci).

Wang. 2004. A spiroplasma associated with tremor disease in the Chinese mitten crab (Eriocheir sinensis)

Glossop et al. Chinese Mitten Crab. Last accessed 26/08/2019

Independent. 2009. WILL WE SOON BE TUCKING INTO MITTEN CRABS FRESH FROM THE THAMES?. Last accessed 26/08/2019

Clark. 2011. The Commercial Exploitation of the Chinese Mitten Crab Eriocheir sinensis in the River Thames, London: Damned if We Don’t and Damned if We Do

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JPPetersen. 2019. [CC BY-SA 4.0 (

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J. Patrick Fischer. 2008. [CC BY-SA 3.0 (

All other images are public domain and do not require attribution

Diatoms-My house of glass

by Matthew Norton

The seas of the world are full of chemical mixtures, not just the sodium chloride that makes up table salt, and many living things are able to extract these chemicals directly from the water for their own purposes. In some cases, they have been quite inventive, using chemicals that most other creatures would not look twice at (assuming they have eyes).

Diatoms, a group of microscopic algae (i.e. seaweeds), are one such group who have devised a way of extracting silica (also called silicon dioxide) from the water and using it to make protective cases out of glass. These cases are called frustules and they come in a variety of shapes (e.g. square, circular, long and thin) and the diatoms that make them may live alone, or joined together in a chain.

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Diatoms do really come in kinds of the shapes and sizes and these images are only a few examples.

We don’t really know the exact process that diatoms use to make their glass cases and given the wide variety made by different species it is possible that there is no single process used by all diatoms, but there are some things we do know. We know that the amount of silica available can control diatom growth, although the ‘pools’ of silica they can store in their bodies may give them an edge when supplies from the water are running low. We have also made some progress in identifying the genes that ultimately make the proteins that grab the silica molecules from the water and transport them to where they are needed in the diatom cell. In recent years, we have also discovered some strange molecules in diatom cells which may yield further clues, but only time will tell.

The glass cases made by diatoms demonstrates how resourceful these little seaweeds can be, but it comes with the problem of glass being very heavy and this extra weight could drag them into deeper water, out of reach of the sunlight they need to make their food. Diatoms rise to the challenge by using their vacuoles, a closed off space inside their single-celled bodies, as a float. They can also make their whole body (except the glass case) heavier during the day by using sunlight to accumulate food reserves and then burn through those reserves to make themselves lighter when they have sunk too far away from the sunlight.

Despite the difficulties that come with living in a glass case, diatoms are a very successful group of organisms who are found floating around in coastal seas, living under sea ice in polar waters and various other habitats in the water and even on land to some extent. They also fulfil a very important role in the world’s oceans, supporting many ocean food chains through sheer numbers at both the surface and as their dead bodies sink into the ocean depths as particles of ‘marine snow’.

The influence of diatoms on the natural world is particularly dramatic when there are rapid explosions in diatom growth called ‘blooms’, but this is not always good for other creatures in the area. For example, anything living under the bloom may suffocate as the dead diatoms suck out all the oxygen as they rot. Some diatom species also release toxic chemicals into the water which can cause serious health problems to animals that get themselves caught in their blooms.

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Some diatom blooms are so vast that they can even be seen from satellites.


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Diatom blooms really can turn nasty under certain conditions and make things unpleasant, even dangerous, for us and any wildlife in the area.

Diatom evolution has produced some pretty impressive techniques for turning a readily available resource into a valuable tool for survival. This seems to have made them a very important part of the ocean ecosystem, which is not bad for a bunch of microscopic plants that we can’t even see with the naked eye.

From a human perspective

There is little doubt that diatoms find their glass cases useful, otherwise they wouldn’t go to the trouble of making them, but we have also found quite a few uses for them because they are durable, long lasting and come in a variety of microstructures.

For example, the glass cases from long dead diatoms can give us vital clues on what life was like millions of years ago through fossilised samples. The patterns of the preserved diatom cases can be compared to the patterns from modern day diatoms and use to the closest matches to work out what the environment was like when the fossilised diatom was alive. Diatom mats on the sea floor can also help to keep the remains of dead animals intact, eventually producing some very well preserved fossils.

Diatoms are also useful in modern detective work by providing forensic investigators with evidence to determine the exact cause of death in victims who have ‘appear’ to have drowned. This is based on the idea that if the victim really did die from drowning in the water body (lake, river, canal etc) that their body is found than they would have inhaled the diatoms from that water body and those diatoms would have been circulated around the body. This can be confirmed by comparing taking samples from the water body and the victim’s major organs and bone marrow and seeing if there is a match. If there is a large difference between these samples then it may suggest that the victim’s body was moved after they had died, which would be very suspicious indeed.

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For forensic investigators, diatoms can be a very useful source of evidence to rule out (or not rule out) homicide in cases of drowning.

It is worth noting that diatom sampling is not a perfect forensic tool for determining a cause of death and there are several circumstances that can produce misleading results. For example, if the victim drowned quickly then any diatoms they inhaled might not have had the chance to get round the body before their circulation shut down. On the other hand, if the victim’s body isn’t discovered for a long time after death then decomposition can directly expose the major organs to the water and the diatoms it contains. Still, diatoms can provide a useful source of evidence in potential homicide cases, even though other pieces of evidence are needed for a conclusive result.

Finally, there has been some interest in using diatom cases in nanotechnology to design micro-electronic devices, chemical sensors and drug delivery systems inside the human body. The advantage to using diatoms is that they we don’t need extreme conditions (e.g. extreme heat to melt metal) to modify the microstructure of their cases, although some clever genetic engineering is still required. There have also been some pretty bold claims that diatom-based nanotechnology can be used to extract tiny particles of silver and gold and make new materials by using the glass case a mould from which the silica can be replaced at the atomic level. This might actually be a step towards creating a machine very similar to the replicators seen in Star Trek.

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It is truly remarkable how diatom-based nanotechnology could be applied in so many different ways.

It is amazing to think that, through the production of their detailed glass cases, diatoms are so useful to us and in some cases they really can change a person’s life. It seems that human innovation and the result of millions of years of evolution is a winning combination that can be applied to a number of problems in our modern world.

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Thanks for reading


Wikipedia. 2019. Diatom. Last accessed 29/07/2019

Martin‐Jézéquel et al. 2000. Silicon metabolism in diatoms: implications for growth

Moore and Villareal. 1996. Size‐ascent rate relationships in positively buoyant marine diatoms

Waite et al. 1997. Sinking rate versus cell volume relationships illuminate sinking rate control mechanisms in marine diatoms

Smetacek. 1985. Role of sinking in diatom life-history cycles: ecological, evolutionary and geological significance

Granata. 1991. Diel periodicity in growth and sinking rates of the centric diatom Coscinodiscus concinnus

Armbrust. 2009. The life of diatoms in the world’s oceans

Sumper and Brunnner. 2008. Silica biomineralisation in diatoms: the model organism Thalassiosira pseudonana

Smetacek et al. 2012. Deep carbon export from a Southern Ocean iron-fertilized diatom bloom

Miralto et al. 1999. The insidious effect of diatoms on copepod reproduction

Harding and Chant. 2000. Self-sedimented diatom mats as agents of exceptional fossil preservation in the Oligocene Florissant lake beds, Colorado, United States

De NYs and de Wolf. 2001. 13 Diatoms as indicators of coastal paleo-environments and relative sea-level change

Krstic et al. 2002. Diatoms in forensic expertise of drowning—a Macedonian experience

Verma. 2013. Role of diatoms in the world of forensic science

Scott. 2016. How microscopic algae are helping forensic teams catch criminals. Last accessed 29/07/2019

Bozarth et al. 2009. Diatoms in biotechnology: modern tools and applications

Schrofel. 2011. Biosynthesis of gold nanoparticles using diatoms—silica-gold and EPS-gold bionanocomposite formation

Drum and Gordon. 2003. Star Trek replicators and diatom nanotechnology

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Derek Keats from Johannesburg, South Africa. 1998. [CC BY 2.0  (].;

Derek Keats from Johannesburg, South Africa. 1998. [CC BY 2.0  (].

George Swann. 2006. [CC BY-SA 3.0].

West Midlands Police from West Midlands, United Kingdom. 2012. [CC BY-SA 2.0 (].

Tim Houlihan. 2008. [CC BY-SA 3.0 (].

Jiangtao12345. 2019 [CC BY-SA 4.0].

All other images are public domain and do not require attribution

Elegant anemone-Clone of my own

by Matthew Norton

In the natural world, creating the next generation is a complicated process with multiple ways for animals to reproduce. The coming together of a male and female to create new life (sexual reproduction) provides each of their offspring with a unique mix of their genes. This helps to keep the variety of genes in the species high, which in turn creates a high variety in all the features that genes control (e.g. body size, eye colour) and gives evolution more options to work with. However, there are some species that use the older method of producing exact copies of themselves (asexual reproduction).

Elegant anemones, Sargatia elegans (not to be confused with Actinoporus elegans), produce their identical clones from bits of their body that break off as they crawl along the seabed. This can allow elegant anemones to rapidly take over sections of the seabed with sheer numbers. They are also well equipped to defend their territories, using their long stinging tentacles to drive away corals, sponges and other anemones. However, this is not a perfect defence and some bacteria are able to slip through the net and live in elegant anemones’ tentacles.

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Elegant anemones stand out with their banded colour pattern and the jagged outline on their base (not visible here) which is a tell-tale sign of their reproduction through fragmentation.

Of course, there are drawbacks to how elegant anemones reproduce. For example, they do not release their young into the water to be carried away by the currents (as is the case with many other marine species), which can make it difficult for elegant anemones to disperse into new areas. Also, because they rely on producing identical clones, elegant anemone populations may struggle to adapt to changes in their environment because evolution have fewer sets of genes to work with. For example, elegant anemones have been wiped out from some areas of the seabed around the Netherlands following a severe winter.

Surprisingly, elegant anemones have managed to overcome their limitations and distribute themselves over large areas of the world’s oceans with reports in 2013 of their spread into the Black Sea. Also, their populations seem to have surprisingly high variety of genes, which suggests that each population was founded by multiple anemones with different genes. In theory, this is possible if these founding anemones came from different populations that were separated from each other and allowed to develop different sets of genes over time before being brought together at a later date.

There is a common misconception that creatures with simple features, such as asexual reproduction, are in some way less evolved. However, the truth is that evolution only provides each species with the upgrades that they need, and not every species needs to be so complicated. It is also worth mentioning that even without sexual reproduction, there are various ways that an animal’s genes and physical features can change over time and give evolution the tools it needs.

From a human perspective

A lot of sea creatures have evolved weapons for attacking prey and defending themselves from predators and unfortunately we can sometimes get caught in the crossfire. In the case of elegant anemones, and other Sargatia anemones, their tentacles are loaded with special stinging cells called nematocysts.

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All cnidarians (e.g. jellyfish, anemones, corals) have these microscopic harpoons tipped with toxins that can produce a nasty sting.

These stings are a particular danger to fishermen who collect the sponges that live among Sargatia anemones and may then suffer from sponge fishermen’s disease, also known as Sargatia’s dermatitis. This condition can include some nasty symptoms, such as burning/itching sensations, redness of the skins and blisters, which can then develop into ulcers and abscesses. In more extreme cases victims suffer from nausea, vomiting, fever and muscle spasms.

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Portraits of sponge fishing seem to date back to at least the 19th century which probably means there have been sufferers of sponge fishermen’s disease since then.

Apart from their stings, elegant anemones do not appear to have any other connections with our lives. However, I would like to suggest some ideas on how these anemones may still be useful to us, especially in scientific research. For example, their strange way of reproduction may make them a species of interest for genetic research (the study of genes), particularly in how genes change over time without sexual reproduction. This idea was explored (sort of) in a 1929 experiment where several anemones, including elegant anemones, were studied to compare their very different ways of reproducing, although genetic research was a very new science back then.

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The 1929 study on several sea anemones included species that can reproduce through cutting off fragments from their base (left), species that are hermaphrodites (both male and female) and practice sexual reproduction (middle) and species where new anemones stretch out from their parents and then snap off (right).

Their ability to easily produce identical clones of themselves could also make useful ‘lab rats’ for all kinds of laboratory experiments. Especially, because this (almost) removes a common source of confusion with the results of these experiments, the difference in genes among the test animals. However, we do need to be careful because genetic differences between animals are an important part of the natural world and without them the results of these experiments may not be that useful.

There are also practical reasons why elegant anemones are useful test animals to keep in a laboratory, despite their stinging tentacles. It is easy to get lots of them to work with by collecting the fragments from a few wild caught anemones and, being quite simple animals, all you only really need to provide them with food and the right living conditions in a small water tank. Also, because of their limited ability to disperse into new areas, elegant anemones are unlikely to escape from the laboratory and invade new areas of the seabed, although such escapes should still be prevented where possible. Not only would these potential invaders be stuck to one area, but they would likely struggle to adapt to their new surroundings. There are even records of an elegant anemone invasion in Massachusetts in 2000 eventually failing by the end of the decade.

In this article I have included some ifs, buts and a lot of blue sky thinking with not much evidence to back it all up. In all honesty, the nasty effects of elegant anemone stings was all I really had and I didn’t have much luck in finding particular incidents to talk about. However, I think it is always worth imagining how else the creatures of the sea might affect our lives, especially as there is so much of their world that we know nothing about.

Elegant anemone blog article image 5
Thanks for reading


Wikipedia. 2018a. Sargatia elegans. Last accessed 09/06/2019

Wikipedia. 2018b. Elegant anemone. Last accessed 09/06/2019

Marine Species Identification Portal. Sagartia elegans. Last accessed 09/06/2019

Schuett and Doepke. 2009. Endobiotic bacteria and their pathogenic potential in cnidarian tentacles

Ates et al. 1998. The occurrence of Sagartia elegans (Dalyell, 1848)(Anthozoa: Actiniaria) in the Netherlands

Shaw. 1991. Effects of asexual reproduction on population structure of Sagartia elegans (Anthozoa: Actiniaria)

Bengtsson. 2003. Genetic variation in organisms with sexual and asexual reproduction

Grebelnyi and Kovtun. 2013. A species of sea anemone Sagartia elegans (Dalyell, 1848) (Anthozoa, Actiniaria, Sagartiidae) that is new for the Black Sea and is capable of clonal reproduction

Bonamonte et al. 2016. Aquatic Dermatology: Biotic, Chemical and Physical Agents

Elston. 2007. Aquatic antagonists: Sponge dermatitis

Wells. 2013. The failed introduction of the sea anemone Sagartia elegans in Salem Harbor, Massachusetts

Stephenson. 1929. On methods of reproduction as specific characters

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Learning by action; Stichting Natuurbeelden. 2010 [CC BY-SA 3.0 nl (

All other images are public domain and do not require attribution


Orcas-Silent running

by Matthew Norton

When it comes to feeding yourself in the sea, different prey use different antipredator adaptations which in turn requires the predator to use different methods to catch their prey. This makes things interesting for opportunistic predators, who target a variety of different prey species and so must be flexible in their hunting strategy, such as orcas (also known as killer whales). The diet of these large dolphins includes fish, sharks, squid and a range of marine mammals, but each orca population, of which there are many, target only some of these prey species and seem to ignore others.

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Orcas hunt various animals that include (clockwise from top left) fish such as herring, salmon and even large sharks as well as seals, porpoises, dolphins, humpback whales and even the occasional octopus or squid.

The most well known difference in the prey that orcas target is between resident populations, who stay in one area and eat fish, and transient populations, who move from place to place and attack other marine mammals. The fish-eating orcas also rely more on echolocation (they produce high frequency ‘clicking’ sounds that bounce off solid objects in the water) to find their food whereas mammal eating orcas are more likely to listen out for their prey without making any sound themselves.

Echolocation would be just as effective in detecting marine mammals as it would for fish, but marine mammals are more likely to hear those high frequency ‘clicking’ sounds, especially dolphins who use echolocation themselves, and be warned of approaching orcas. Even for these powerful predators, the element of surprise can be vital to the success of a hunt with even large whales sometimes running away if they hear orcas coming.

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Echolocation is used by many toothed whales (a group that includes all dolphins ) to find food by sending out high frequency ‘click’ sounds and listening for the echoes that are bounced back when the clicks hit something solid in the water. Using these clicks they can make a mental map of their environment, including the location of a potential fish.

Even between fish-eating orca populations (and probably marine mammal eating populations) there are differences in the prey species they target and the hunting strategies they use. For example, orcas living in Norway and Iceland catch herring by herding them into tight groups and then slapping their tails to stun the fish.

Meanwhile, the shark and ray eating orcas found around New Zealand and Australia (although orcas have been seen eating sharks elsewhere in the world) can use various hunting methods to handle these tricky prey. These include grabbing bottom dwelling rays by the tail with their teeth and dragging them out of hiding places, sometimes with the orca’s tail hanging out of the water, using tail slaps to confuse sharks and even flipping white sharks on to their backs to immobilize them. It is worth mentioning that reported cases of orcas eating sharks and rays are rare and these hunting behaviours could be one-off, or could be one of many unique shark hunting techniques used by orcas.

The different hunting techniques that orcas have developed are all part of the continuing battle of wits that evolution creates between every predator and prey combination. This in return has lead some of the orca’s prey species to evolve clever antipredator responses, with some fish being able to hear the high frequency sounds used in echolocation and smaller dolphins using sounds that are outside an orca’s hearing range. Nonetheless, orcas are still one of the seas most impressive and effective predators.

From a human perspective

It was difficult to know where to start for this section, orcas have affected our lives for so long by being a source of wonder in the seas and a source of inspiration in television and film with the Free Willy films being particularly famous. Sadly, many orcas who came into contact with humanity were abducted from the wild and forced into a life in captivity for our entertainment. Fortunately, the harm caused to orcas by a life in captivity has received worldwide attention since the documentary “Blackfish” came out and sparked major protests against aquariums that still keep whales and dolphins in captivity.

Even in their natural environment, orcas may not be completely safe from humans meddling in their lives, they do share the seas with us after all. For example, our boats can sometimes disturb wild orcas if they live around a busy shipping lane, or are approached by a whale-watching boat that gets too close. As isolated incidents, these disturbances may not cause the orcas too much harm, but if they are repeated over and over again then it may cause them to waste a lot of their valuable time and energy while avoiding our boats.

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We make noise in the sea through all kinds of activities including pile driving to set up wind turbines, engine noise from boats and the sonar from submarines.

Worse still, the noise pollution from some of our activities at sea, which include general boat traffic, sonar from submarines and pile driving (i.e. slamming a large piece of metal into the seabed), can disturb orcas and other marine wildlife that are nowhere near us. All that noise makes it harder to be heard in the ocean, which is especially bad for social animals like orcas that use various calls to talk to each other. Noise pollution can also drive orcas away from the surrounding area for long periods of time, which in some cases is the intended effect with humans using noise to keep marine mammals away from fish farms and to round up whales and dolphins to take into captivity.

These are the impacts of noise pollution on orcas that we know about, but it is worth pointing out that noise pollution has a whole range of effects on sea life. In the most extreme cases it can actually damage the ears, or whatever other structure an animal may use to hear, and cause hearing loss. In other cases, noise pollution can lead to dangerous behavioural changes such as unusual aggression, a lack of response to certain sounds and for whales and dolphins, panic and disorientation during dives which could lead to decompression sickness. Even though these effects of noise pollution have not been specifically reported in orcas (as far as I know) they could still be happening.

Noise pollution is one of many threats that marine life is facing in the modern world and while the world under the waves is a naturally noisy place, the loud sounds that we make are certainly an unwelcome addition.

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Thanks for reading


Wikipedia. 2019. Killer whale. Last accessed 06/05/2019

Au et al. 2004. Echolocation signals of free-ranging killer whales (Orcinus orca) and modeling of foraging for chinook salmon (Oncorhynchus tshawytscha)

Ford and Ellis. 2014. You are what you eat: foraging specializations and their influence on the social organization and behavior of killer whales

Simon et al. 2007. The relationship between the acoustic behaviour and surface activity of killer whales (Orcinus orca) that feed on herring (Clupea harengus)

Barrett-Lennard et al. 1996. The mixed blessing of echolocation: differences in sonar use by fish-eating and mammal-eating killer whales

Deecke et al. 2005. The vocal behaviour of mammal-eating killer whales: communicating with costly calls

Cure et al. 2015. Predator sound playbacks reveal strong avoidance responses in a fight strategist baleen whale

Van Opzeeland et al. 2005. Vocal behaviour of Norwegian killer whales, Orcinus orca, during carousel and seiner foraging on spring-spawning herring

Simon et al. 2005. Acoustic characteristics of underwater tail slaps used by Norwegian and Icelandic killer whales (Orcinus orca) to debilitate herring (Clupea harengus)

Wilson and Dill. 2002. Pacific herring respond to simulated odontocete echolocation sounds

Astrup and Mohl. 1993. Detection of intense ultrasound by the cod Gadus morhua

Morisaka and Connor. 2017.Predation by killer whales (Orcinus orca) and the evolution of whistle loss and narrow‐band high frequency clicks in odontocetes

Holt et al. 2009. Speaking up: Killer whales (Orcinus orca) increase their call amplitude in response to vessel noise

Morton and Symonds. 2002. Displacement of Orcinus orca (L.) by high amplitude sound in British Columbia, Canada

Williams et al. 2006. Estimating relative energetic costs of human disturbance to killer whales (Orcinus orca)

Williams et al. 2014. Severity of killer whale behavioral responses to ship noise: a dose–response study


Gabbatiss. 2019. Dolphins’ psychological trauma after being hunted for marine parks revealed in new research. Last accessed 06/05/2019

All images are public domain and do not require attribution

Flatworms-Living without a heart

by Matthew Norton

The insides of many animals are made up of blood vessels, nerves, muscles and organs (and more) working together as one complicated machine with each small part performing specific tasks to keep this machine working properly. How easy it is to forget that not all animals are, or need to be, this complicated, with some weird animals groups able to survive without the major components that we need to live.

Flatworms (also called Platyhelminthes) are one such weird group of animals that come in a wide range of body forms, even though their basic biology is very simple, with some ‘vital’ organs completely missing. For example, they have no heart, gills, or circulation system for extracting oxygen from the environment and pumping it around their body. Instead, they simply rely on the oxygen to flow through their bodies, a process called diffusion, but this only really works over small distances, which is probably why flatworms are flat and/or small.

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Flatworms are definitely a weird and varied group of animals with examples including (clockwise from top left) Turbellerians, Trematodes, Tapeworms and Monogeans.

Even the few organs that flatworms do possess are very simple in design with the digestive system being just a fleshy sack instead of a system of different compartments (stomach, small intestine, large intestine etc) for different stages of food digestion. Some species don’t even have an anus for getting rid of waste and have to vomit this waste back out through their mouths. Their nervous system is also very simple, although they do have a clump of nerves at one end of the body which could be a brain.

Clearly, flatworms have very little to work with and you wouldn’t expect them to do anything interesting. Many flatworm species cannot even function on their own and survive as parasites on animals that include fish, crabs, snails, frogs and even humans. Other species however, can live on their own and catch their own prey by waiting to ambush them, trapping them in nets of sticky mucus, or poisoning the water around them.

Flatworms also demonstrate some interesting social behaviours despite their primitive brain, if it even counts as a brain. This is well demonstrated by Pseudobiceros bedfordi, a species that meet in pairs and fence with their penises. Like many flatworms they are simultaneous hermaphrodites (which means each animal is both male and female at the same time), but each animal would prefer the other to ‘be the female’ and do the job of carrying the fertilised eggs. Neither animal develops a specific opening for the sperm so the ‘fencers’ will try to burn a hole in each other with acid, while trying to avoid being burnt themselves.

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Both these Pseudobiceros bedfordi flatworms have the common goal of reproduction, but the one that carries the fertilised eggs will have to spend a lot more energy dragging them round.

A common misunderstanding with evolution is that it aims to produce some sort of perfect organism in the long term, but really it works to change a species one small step at a time and equip it with what it needs to survive, and nothing more. The complicated machinery that support many large animals is just one of many options to help animals survive in the natural world and it is an option that flatworms don’t need.

From a human perspective

Unfortunately, when it comes to the interactions between us and flatworms it is the parasitic species that stand out, and with good reason. The flatworm group includes some nasty parasites that can infect various parts of the body including (but not limited to) the blood, liver and intestines and can cause serious health problems. One particular case from 2017 where a 17 year Mexican teenager who had somehow got a tiny flatworm burrowing around inside his eye. The flatworm was successfully removed, but it left the teenager with a permanently damaged eyeball.

On a wider scale, several species of flatworm parasite are also responsible for Schistosomiasis (also known as snail fever) which is the world’s 2nd most devastating disease caused by a parasite after malaria. Symptoms are varied and include blood in the urine, pain in the genital area, stunted growth, infertility and reduced learning ability, all of which are harmful, but rarely cause death directly. Victims can become infected with Schistosoma flatworms from any contact with water that contains their larvae, whether they are drinking it, bathing in it, or washing their clothes in it. The water itself can become infectious from releases of flatworm larvae by infected snails, or the faeces of infected humans, which can contain flatworm eggs.

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Without access to clean drinking water and good sanitation there is a serious risk of picking up a Schistosomiasis causing parasite.

Without access to clean drinking water and good sanitation there is a serious risk of picking up a Schistosomiasis causing parasite. Image source: Bb.braam, 2017 (right, CC BY-SA 4.0).Flatworms can also cause us serious economic problems by attacking other animals that we rely on. A number of flatworm parasites can infect livestock, farmed fish and shellfish, making the meat unsuitable for human consumption and costing the farmers considerable amounts of money. Even non-parasitic species can be a problem, for example some Bipalium flatworms, such as the New Zealand flatworms, have been massacring earthworms in Northwest Europe. This is bad because earthworms are an especially valuable species because they can be a protein rich food source for our livestock and a useful decomposer of food waste.

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New Zealand flatworms (Arthurdendyus triangulates) and their relatives are invasive species in Northwest Europe.

Despite all these negative effects, some flatworms can help us to develop useful ideas to our problems. In particular, the ability of Planarian flatworms to clone themselves from tiny fragments the original body may hold insights for stem cell research. There has also been interest in using certain species planarian and turbellarian flatworm, and their consumption of insect larvae, as natural controls against mosquitos.

Survival in the natural world does not usually encourage niceness to other animals, especially towards different species, and in some cases we can get caught in the firing line. However, this is nothing compared to the impacts (e.g. climate change, overfishing, plastic pollution) that we have on the environment, both above and below the waves. No other species on earth manipulates the world around them like we do.

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Thanks for reading


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Shipworms-Shiver the timbers

by Matthew Norton

Life under the sea is not easy for most animals with the search for food being a constant challenge. Often, there is not enough to go around and this can lead to fierce competition over access to what little food there is. Some species get out of this difficult situation by specialising on those foods that most animals wouldn’t want to eat because they are low in nutritional value and hard to digest. So long as the food source can provide the basics to support life, which include (but are not limited to) carbon for making glucose sugars and nitrates (or other nitrogen based compounds) for making proteins and DNA, then it can be a viable food source.

For shipworms, which are worm-like clams, the food of choice is wood and they can burrow into submerged wooden structure, such as trees, boats and piers, and slowly grind it into tiny pieces. They dig into the wood by using a pair of sharp shells at one end (which in other clams would encase the whole animal) to grind away the wood and then pushing their body in. As they move in, shipworms line their burrows with a mixture containing calcium carbonate (which most hard body parts, such as bones and shells are made of) to prevent them from collapsing.

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Shipworms are weird, but resourceful animals that completely repurpose their shells, which other bivalve molluscs (e.g. oysters) use for protection, to drill their way through wood.

All this burrowing breaks the wood down into the pieces that shipworms can swallow, but actually digesting the wood material, specifically the cellulose fibres, into glucose sugars that the animal needs is not so easy. In fact, they cannot do it themselves and instead rely on one specific strain of bacteria, called Teredinibacter turnerae T7901, to make the necessary enzymes (molecules designed for making or breaking chemical bonds) for breaking down cellulose.

Bacteria also help shipworms to overcome the other problem with a wood diet, a lack of nitrogen, by extracting dissolved nitrogen from the water and converting into more usable forms. Although, there is some evidence that shipworms also catch food particles floating in the water to supplement the nitrogen in their diet.

Shipworms (with help from their bacteria) are so well adapted to living in wood that once the larvae settle on a suitable block of wood they never leave, with the giant shipworm, Kuphus polythalamia, being the only exception. This species, already noteworthy because of their sheer size, leave their wooden burrows in their youth and instead settle for a life buried deep in muddy seabeds. Without wood to eat they rely on a different strain of bacteria (Thiosocius teredinicola) to make them glucose sugars from carbon dioxide dissolved in the seawater, similar to how plants and seaweeds make their food by photosynthesis. However, a giant shipworm’s bacteria uses chemical energy, instead of light energy, released from reacting sulphides with oxygen or nitrogen-based compounds to power this conversion.

The use of bacterial helpers to boost an animal’s chances of survival is common in nature, even we have thriving communities in our guts that massively outnumber our own cells and provide all kinds of health benefits. However, shipworms take this one step further and use their bacteria to exploit a unique food source and mould their own place in the natural world.

From a human perspective

Because shipworms eat wood, they have been a serious pest for mariners and coastal communities through history, causing serious damage to boats, piers, harbours and any other man-made wooden structure submerged in seawater. This problem is particularly hard to manage because shipworms are so small when they first enter the wood that infestations are only discovered when it is too late. Even inland seas, such as the Baltic Sea, are not safe because of one particular species, Teredo navalis, which is particularly effective at infesting areas that most other shipworms cannot.

The damage and frustration that shipworm infestations can cause is pretty clear from the epidemic that plagued the coasts of the United States during the late 19th and early 20th century. The damage itself cost millions of dollars per year, but some coastal communities were relatively unaffected while others were devastated by shipworm infestations and this led to a lot tension. Teredo, a general term for shipworms at the time, was also used as an insult targeted at certain political groups and ethnicities.

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The first Herne Bay peer, depicted in this postcard, was also devastated by shipworms burrowing in the wooden pillars that were not protected by copper plates.

Fortunately, shipworms are also useful because of their unique way of living. For example, in the 1990’s there was a lot of interest in the commercial uses of the enzymes produced by shipworm bacteria to remove stains and contaminating chemicals. These cleaning enzymes do not work at very high temperatures, but they must still be effective if certain entrepreneurs went to the trouble of patenting their use.

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The enzymes produced by shipworms’ bacteria can be used for various purposes, such as sterilising contact lenses, cleaning industrial machinery and as an ingredient in detergents.

Shipworm burrowing also inspired the French engineer Marc Brunel (not to be confused with his more famous son, Isambard Brunel) to invent the “tunnelling shield” technique in the early 19th century for burrowing underground. This involves using a movable ‘shield’ as a temporary support structure (sort of like scaffolding) while workers dig and build concrete walls around the tunnel. This was so effective that Brunel used the tunnelling shield to build the Channel Tunnel that connects the south of England and the north of France (under the English Channel).

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On the right hand side you can see the tunnelling shield that holds up the tunnel while the rest of the tunnel is built up with concrete wall. This approach was so effective during Brunel’s time that it is still used today.

Shipworms are both pests and a useful source of ideas with a certain historical importance in their impact on our lives. However, I suspect that most people focus on the damage that they cause, which I think unfair as this is really a problem of our own making. Through centuries of building wooden structures in the sea we likely caused rapid increase in shipworm numbers by providing with far more habitat than they would have normally had. Such are the long-lasting consequences of our meddling with the ocean’s ecosystem, consequences that we rarely see coming.

shipworm article image 5
Thanks for reading


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Pufferfish-A dangerous delicacy

by Matthew Norton

The sea is a dangerous place to live with many of its creatures under threat from bigger animals that want to eat them. Therefore, it makes sense to have defences in place, such as a hard shell to protect their soft flesh, a flexible body to squeeze into tight hiding places, or strong, muscular fins to quickly swim away from danger. Other sea animals produce and store toxic chemicals in their organs, which will poison any predator foolish enough to eat them.

For many species of pufferfish, the weapon of choice is tetrodotoxin which is a nasty neurotoxin that disrupting the electrical signals that pass through an animal’s nervous system. Under normal circumstances these signals are transmitted by the movement of electrically charged sodium ions in and out of the nerve cells, which moves the signal along (like a Mexican wave in a crowd).

Tetrodotoxin blocks the channels through which the sodium ions re-enter the nerve cells which, depending on the dose, weakens, or completely blocks the transmission of these electrical signals. Without properly functioning nerves the brain of the poisoned animal will struggle to tell it muscles to move, resulting in symptoms such as muscle weakness, paralysis and breathing problems.

Pufferfish article image 1
Pufferfish accumulate tetrodotoxin in their skin, liver, intestines and ovaries (depending on the species) which makes them deadly for most animals to eat.

Tetrodotoxin is clearly an effective deterrent against predators, but there are ways to develop a resistance to tetrodotoxin, such as changing the structure of the sodium ion channels, otherwise pufferfish would also suffer from its effects. Even predators with limited tolerance to tetrodotoxin, or no tolerance at all, may still be able to eat pufferfish without getting poisoned for two very good reasons.

Firstly, the toxicity differs between pufferfish species, which suggests that some species need less protection, or rely more heavily on other means of protection, such as puffing their bodies up, or sudden bursts of swimming activity.

Secondly, in most species, pufferfish are not born with tetrodotoxin defences, in fact they cannot produce the toxin themselves and instead keep cultures of toxin-producing bacteria in their bodies. They get these bacteria from their prey, who in turn get them from further down the food chain, but until they can accumulate a meaningful amount of tetrodotoxin from these bacteria they will be vulnerable to predators. The only exceptions are species who can accumulate the toxin in their ovaries, such as the Grass Puffer, Takifugu niphobles, and pass it on to their larvae.

This diagram roughly shows the process that tetrodotoxin interferes with. Sodium (Na+) ions are drawn into the nerve through open ion channels (left side) and flips the electrical charge inside the nerve from positive (+) to negative (-). Some of these sodium ions are drawn further down the nerve to where it is still negatively charged (positive and negative charges always attract), which opens up the next set of sodium ion channels and the cycle is repeated.

Pufferfish have adopted a strong anti-predator defence with their use of tetrodotoxin, but this strategy still has its limitations, which is probably why they have other defences in place. Some marine animals, such as cone snails and arrow worms, have even repurposed the toxin for catching and paralysing their prey, rather than defence. Nonetheless, the use of toxic chemicals for defensive purposes is still an inventive solution in the struggle to survive and not get eaten.

From a human perspective

There are a number of different animal groups that are poisonous to eat because they contain tetrodotoxin, but tetrodotoxin from pufferfish is worth paying attention to because we eat them. Human consumption of pufferfish is possible because the muscle of most species has very low concentrations of tetrodotoxin, which can be removed prior to consumption, and farmed pufferfish can be deprived of their supply of toxin-producing bacteria.

Unfortunately, there are still cases of tetrodotoxin poisoning, especially in Japan and the United States, due to pufferfish meat not being prepared properly, or a being labelled as a completely different, non-toxic, fish. This potentially fatal mistake (for the consumer) was even depicted in an episode of The Simpsons in which Homer Simpson thought he had eaten toxic pufferfish meat and only had 24 hours left to live.

Pufferfish is a seafood delicacy, especially in Japan and the United States, but because of the danger posed by tetrodotoxin in its flesh it has to prepared in restaurants by specially trained chefs.

Fortunately, we can also use tetrodotoxin as a painkiller by reducing the dose to a safe level (relatively speaking) that only weakens the electrical signals in affected nerves, specifically the nerves that tell the brain to feel pain from a specific body part. In modern medicine there it can be used to relieve pain in patients recovering from surgery and suffering from medical conditions that include arthritis, cancer and injuries to the spine and knee joints. Some evidence also suggests that pufferfish meat and eggs, which contained tetrodotoxin, was used in historical medical practices to treat arthritis, leprosy and muscle convulsions.

Tetrodotoxin may be a poison, but carefully controlled doses can, and have, been used to relieve pain from certain medical conditions such as arthritis (top right) and leprosy (bottom right).

Non-fatal doses of tetrodotoxin from pufferfish may also be used insidious purposes such as voodoo zombification. Stories of this practice, where the recently deceased are believed to be magically raised from dead by a voodoo priest, or priestess, originated in Haitian folklore among slaves brought from Africa in the 18th century. These stories received more widespread attention in the western world in the early 20th century and was soon depicted in western literature and early zombie films such as “White Zombie”.

Tetrodotoxin’s role in voodoo zombification was suggested in the 1980’s by Wade Davis, an anthropologist (the study of humans) from Canada who suggested that the practice is partly based in reality. Instead of magic, he suggested that a special ‘zombie powder’ applied the by voodoo priest/priestess contained tetrodotoxin, extracted from pufferfish, caused a death-like state in the victim, who seemingly rises from the dead as the toxin wears off.

In Haitian folklore voodoo zombies remain under the control of the priest or priestess as personal slaves, which directly inspired the 1932 film called “White Zombie” (right).

Davis’s claims were controversial at the time, and remain so to this day for a variety reasons. These include specific criticisms over how Davis conducted his research while he was in Haiti, such as confusion around the samples of zombie powder he collected and the fact he didn’t test its effects on mice. There were also personal attacks against Davis, such as claims he was involved in morally questionable activities in Haiti and that, by writing two popular books, he was exploiting the publicity around his findings. These arguments aside (I’d rather not get involved regardless of their validity) the scepticism over Davis’s claims is well founded, but if they are true it would hardly be the first radical theory to be rejected at first and then widely accepted at a later date. When Charles Darwin argued that species evolve by natural selection and Galieo Galilei argued that the Earth orbits around the Sun they were seen as radical by many people at the time.

It is bizarre to think that this one toxin can poison us, relieve us from pain and make us think we’ve risen from dead. Admittedly, the role of tetrodotoxin in voodoo zombification is questionable at best, much like the existence of the practice itself. However, even the idea that this mythical practice could exist in the real world has a powerful effect on human culture and zombies as an icon in popular culture.

Pufferfish article image thanks for reading
Thanks for reading


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Narahashi et al. 1964. Tetrodotoxin blockage of sodium conductance increase in lobster giant axons

Chau et al. 2011. On the origins and biosynthesis of tetrodotoxin

Noguchi et al. 2006. TTX accumulation in pufferfish

Lee et al. 2000. A tetrodotoxin-producing Vibrio strain, LM-1, from the puffer fish Fugu vermicularis radiatus

Yang et al. 2007. Analysis of the composition of the bacterial community in puffer fish Takifugu obscurus

Matsumura. 1998. Production of tetrodotoxin in puffer fish embryos

Itoi et al. 2014. Larval pufferfish protected by maternal tetrodotoxin

Venkatesh et al. 2005. Genetic basis of tetrodotoxin resistance in pufferfishes

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