Subtidal food thieves: interactions of four invertebrate kleptoparasites with the sea star Leptasterias polaris.

We used time-lapse underwater video systems in the subtidal zone of the Mingan Islands, eastern Canada, to examine behavioural interactions of four kleptoparasites with the sea star Leptasterias polaris when it was feeding on infaunal (buried) clams. Departures of L. polaris from its prey coincided with interactions with kleptoparasites in 10 out of 10 filmed feeding bouts on the large clam Spisula polynyma, compared with only four out of 10 of filmed bouts on the smaller clam Mya truncata. The sea star's abandoning of the prey was most often caused by interactions with another sea star, Asterias vulgaris, a potential predator. The whelk (a carnivorous snail), Buccinum undatum, and the crabs Hyas araneus and Cancer irroratus, also kleptoparasitized L. polaris, especially when A. vulgaris was present. Comparisons of feeding bouts in the presence and absence of kleptoparasites showed that at least 10.4% of the prey mass captured by L. polaris was lost to kleptoparasites. Simultaneous current meter data showed that the movement of A. vulgaris and B. undatum to sites where L. polaris was feeding on S. polynyma was upstream, suggesting chemodetection of food odours. Crabs in the vicinity may also use visual cues. Leptasterias polaris is the only carnivore that can efficiently extract large clams from the sediments and therefore its foraging may supply a substantial part of the diet of kleptoparasites. Copyright 2000 The Association for the Study of Animal Behaviour.