A Common Starfish eating a Spiny Cockle

Well, the Common Starfish is not actually eating the Spiny Cockle just yet – but it is moving in for the kill!

A whole load of marine creatures was washed up after a storm on the causeway between Burry Holms and Spaniard Rocks at Rhossili, Gower. The orange-skinned starfishes (Asterias rubens Linnaeus) were making the most of the situation by homing in on the distressed bivalved molluscs. There was so much debris of one sort or another that the cockles, razor shells and other bivalves could not easily re-bury themselves. The Spiny Cockle shells – Acanthocardia aculeata (Linnaeus) – were gaping wide open while they repeatedly reached out with their large, glistening, red muscular foot to gain a purchase on the wet sediments to pull themselves back down into underground safety. Mostly they were unsuccessful.

The starfishes were taking advantage of the opportunity provided by the mass stranding. They inched forward and over the shells ready to eat the easy pickings. Normally, they would have had to wrap their five arms around the mollusc and sucker on tight with their multitudes of tube feet. By exerting a continuous steady pull, the starfish would aim to tire the muscles that hold the two hinged shells tight shut. Eventually the cockle would become exhausted and gape open, allowing the starfish to eat its prey. 

In this dramatic scene of invertebrate carnage, thousands of small seashore creatures died or were dying. However, for some organisms like the starfishes it was a bonanza.

Revision of a post first published 21 December 2009

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