by Matthew Norton
The seashore is a hard place for marine creatures to live with periodic air exposure, the risk of being dislodged by the waves and wide fluctuations in temperature, salinity and other environmental conditions. Many species escape these harsh conditions by burrowing into the sediment (collective term for sand, mud, muddy sand etc) where they can also hide from predators and gain access to unique food sources, such as buried microorganisms. However, as seawater trickles down its oxygen is depleted by any living thing it encounters, which can seriously restrict oxygen supply for animals buried deep in the sediment.
Some species have devised strategies to overcome this issue, including the lugworm (also known as the blow lug), Arenicola marina, which has developed a particular method of burrowing that helps it to keep a sufficient oxygen supply. These worms contract and expand their bodies in a rhythm that pumps water through their burrows and into the wall of sediment in front of them, which loosens it into smaller clumps. They consume these clumps, which incidentally contains the buried microorganisms that they eat, and then defecate them at the surface as coiled faecal casts.
The water flow generated by the lugworms constantly brings ‘new’ water into the burrow so that they don’t rely on a still body of water, within which the oxygen would be quickly exhausted. The oxygen-depleted water also needs to be drained out to make way for ‘new’ water, which is where burrow architecture comes in. In sand lugworms usually dig J-shaped burrows with an open pore in front of their head where water drains out through the tiny gaps between sand particles. In mud draining water is more difficult with much smaller gaps between the mud particles, so lugworms build U-shaped burrows with a second opening at the surface through which they can expel oxygen depleted water.
Lugworm burrowing also changes the chemistry of their surrounding environment, making it more hospitable to life. In particular the enhanced oxygen supply stimulates its reaction with ammonia, a common product of animal waste, to produce less toxic nitrogen based compounds. Both the oxygen and nitrogen recycling stimulates the growth of microorganisms on the burrow walls, some of which can remove carbon dioxide, another waste product that can be toxic at high concentrations.
However, lugworms can also have a negative impact on various species, such as other burrowing worms who may end up competing with lugworms for food, burrowing space and other resources. Lugworm burrowing may also disturb filter feeding species, who filter out tiny food particles floating in the water, lying on, or just below the sediment surface by smothering them with the sediment they excavate from their burrows.
Lugworms are shining examples of how life can adapt to any lifestyle, even in the face of real hardships. Indeed the masses of faecal casts found on sandy beaches and muddy estuaries demonstrates their status as a major force in structuring the subterranean world.
From a human perspective
Being small and living underground, it is unlikely that lugworms are a widespread attraction for anyone with a causal interest in nature, nor are they popular for human consumption. They are however, an important food source for many fish and wading seabirds, which shows that lugworms have an important supporting role in birdwatching and angling. These are both popular recreational activities and come with a variety of benefits.
Bird watching and angling can improve your physical fitness by getting you out in more natural areas of the countryside which are only accessible by foot. There are also mental health benefits from being in a natural environment, which reduces stress, and from the activity itself with increased concentration and awareness for a bite on the fishing line, or for a good view of a rare bird.
Furthermore both activities can inspire creativity to some extent. For example there was a British comic strip called “Ollie and Quentin”, which ran from 2002 to 2011, about an unlikely friendship between a seagull, Ollie, and a lugworm, Quentin. The premise was that Quentin was very adventurous and got himself into ridiculous accidents as a result and Ollie would try to protect him in a sort of older brother role. The comic’s creator Piers Baker has stated that his inspiration was the lugworms he used as angling bait during his youth.
The contact with nature and wildlife that comes with bird watching and angling can inspire a greater awareness and appreciation for the natural world. As a result anglers and bird watchers can be among the first to notice long term declines in wildlife. For example the Isle of Arran, Scotland, was once a very popular destination for recreational sea angling which drew anglers from all over the country and beyond. It was those anglers who felt the effects of decades of commercial overfishing with declines in fish catches eventually forcing the annual sea angling festival to be cancelled after 1994.
Finally, both activities bring economic benefits for local communities and conservation charities for various reasons. These include the bits of kit required, such as binoculars, identification guides, angling rods and bait, the desire for refreshments and accommodation and travel. The economic contribution can be substantial, for example the United States Fish and Wildlife Service estimate that birdwatcher make an annual contribution of over $30 billion to their economy.
When we watch and interact with wildlife it is easy to overlook small creatures like lugworms in favour of large, charismatic animals. This is a habit we need to break, because not only are the small creatures vital to the existence of more popular wildlife species, but they are also fascinating in the own way. This would be plain to see if lugworms were as large and visible as fish, seabirds and marine mammals. It is really is just a matter of scale.
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