What can be found on the strandline #3 Crab shells

20 January 2021 | Posted in Ella Garrud , Marine
What can be found on the strandline #3 Crab shells
Edible crab © Sarah Ward

The strandline is the high water mark on a beach where waves dump materials which can later be found by discerning beach combers.

Winter is a brilliant time to go beach combing because the stormy weather tends to wash up interesting things onto the strandline more frequently and in greater quantity.

Crab shells

If you find a crab shell in the strandline, it is likely not a dead crab but actually a moulted crab shell. Over their lifetime, crabs moult (or shed) their shell many times as they grow. Once the crab has become too big for its external shell, it will fill its body with water which helps to loosen the old shell, until it cracks along a seam at the back. The crab will then climb, or push itself, out of the back of its old shell. This process can take between 15 minutes and a few hours. The freshly moulted crab already has a new, readymade shell, but it is soft and takes a few days to harden. For this reason it is very vulnerable to predators and must quickly find somewhere to hide.

Spider Crab Shell©Barry YatesSussex Wildlife Trust

Spider crab

Common species to find in Sussex are the common shore crab (Carcinus maenas), edible crab (Cancer pagurus) and the spiny spider crab (Maja brachydactyla). Here is a fantastic time lapse video of a common shore crab moulting its shell.

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