Are sponge crabs on the rise in British Seas, or are we just getting better at finding them? Paul Naylor gets spongey
CRITTERCONFIDENTIAL
Lacking camouflage expertise, with a bright yellow‘ hat’ among pink jewel anemones
Sponge Crab
Are sponge crabs on the rise in British Seas, or are we just getting better at finding them? Paul Naylor gets spongey
Sponge is versatile stuff. As well as being an important part of marine ecosystems, we humans have cleaned ourselves with it and a variety of other animals use it for the more serious job of defending themselves. Some molluscs have
20 shells adapted to attract settling sponge larvae, while those of queen scallops, for example, are often encrusted in orange sponge. The arrangement is thought to be a‘ win-win’ because the sponge gets away from crawling predators such as sea slugs
A different approach; small spider crab with an all-encompassing coat of sponge
Dromia personata
and the scallop benefits from a slippery and unpleasant-tasting coat.
Crustaceans take an even more proactive approach. Those small, spindly spider crabs( Inachus sp) that are such a common sight when you get your eye in carve out little pieces of sponge and attach them to tiny hooks( resembling Velcro) on their armour. The fragments of sponge then grow into a complete protective covering.
Whether sponge provides camouflage, a nasty-tasting deterrent or both, it seems to be well worth having. Strong evidence for this comes from another crab that, while not equipped with‘ Velcro’-hooked armour, has evolved to make strenuous efforts making, holding and carrying a large covering‘ hat’ of sponge.
Meet the bizarre looking sponge crab. I had heard about this unusual species but did not see my first one until 2022. I was tipped off about their presence by one of the enthusiastic and observant Plymouth diving regulars, then lo and behold, on my very next dive in the Sound, there was a sponge crab in front of me. Even aside from its sponge‘ hat’, it has a distinctive and very heavily built appearance. As implied by the alternative name of‘ sleepy crab’ it is unusual to see one moving around. They have rather an ungainly gait but, given half