Sea slaters

Have you ever explored the rocky coastline or a rock pool at the seaside and discovered a monster scuttling over the rocky surface but then disappearing into a crevice before you could get a better look? You probably witnessed a sea slater.

A sea slater is a type of marine isopod species. They are also known as the Sea Roach, Sea Louse or Common Slater. Their scientific name is Ligia oceanica.

They are very comparable to their relative marine and terrestrial isopod species especially when it comes to their appearance. Sea slaters have large, flattened, segmented bodies which have a unique changeable canvas – yellow, green, brown or grey, and often speckled with a variety of black freckles – helping it to blend into the rocky surfaces. It can actively adjust the pigments in its cuticle thanks to cells called melanophores. This colour change is mainly a response to light levels, humidity and temperature. They have large black compound eyes and long antenna which are usually more than half of its body length which is a whopping 3 cm long without their antenna. Like their terrestrial isopod relatives, they have gills but don’t live underwater. Sea slaters have a life span of up to 2.5 years. 

You won’t find a sea slater under the rocks or bark in your garden or local woodlands they prefer rocky coastal locations. They are extremely abundant throughout Britain, Ireland and the rest of Europe. They are also found along the eastern coast of North America, despite not being native to that continent. They are believed to have been transported in the ballest water of ships. Ligia have a permeable skin and gills that are less adapted to land than other terrestrial isopods.

Their habitat is turbulent with unpredictable sea conditions from a light, steady salty sea mist to being totally inundated by large crashing waves. There is also the constant risk of dehydration from both sun and wind. Due to these conditions, sea slaters are rarely seen during daylight hours, making them nocturnal, unless their hiding place has been disturbed. The best time to find them is on a dark, moonless night, although a bright torch beam will send them quickly scuttling for cover on their seven pairs of long legs. 

Like the terrestrial isopod, they play an important role in our coastal ecosystem. They are detritivores and munch on decaying material like seaweed, lichen and they even scavenge on dead animal material. 

Sea slaters themselves can become prey food for a wide range of species, with any fish which scavenges on the seabed, such as cod, whiting, wrasse, rockling, dab or flounder will feed on sea slaters given the opportunity. Despite many species of fish feeding on sea slaters they are not widely utilised as a sea fishing bait by anglers, possibly due to the difficulty of procuring a decent number of sea slaters of sufficient size to mount on a hook.

If you’re planning a trip to the beach, it’s well worth looking out for them but be sure to be careful to leave everything as you found it - replace any rocks you turn over, put back any crabs or fish and ensure not to scrape anything off its rocky home. Sea slaters play an important part of the beach clean-up crew.