This morning I checked the area on Ramsgate main sands where the remains of the velvet swimmer crabs killed off by the sudden drop in temperature during the recent cold snap have been deposited by the tide. Almost all the remains have broken down and I have scanned a example of the back legs of the velvet swimmer crab. As you can see the back legs are flat and act as a paddle. This is an advantage for the swimmer crab when it comes to hunting out prey and escaping predators, unfortunately it does make it difficult for them to burrow in the sand and mud when the water temperature drops. Unless they can find a hole or crevice in the chalk reef to hole up in they are very much doomed when the water temperature drops unless they make it into deeper water.
On another point when searching a sandy rock pool it is noticeable that the common shore crab will burrow into the sand when threatened, a swimmer crab will swim for it and never burrows.
These are the photographs I took by the East Pier Ramsgate of the remains of the velvet swimmer crabs. As you can see the tide has pushed the dead crabs up against the sea wall. Further along the strandline along the shingle are the carapaces stripped clean of flesh by the sea birds taking advantage of the winter kill.