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 Min gan Islands, eastern Canada, to examine behavioural interactions of four kl eptoparasites 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 f ilmed 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, Aster ias vulgaris, a potential predator. The whelk (a carnivorous snail), Buccin um undatum, and the crabs Hyas araneus and Cancer irroratus, also kleptopar asitized L. polaris, especially when A. vulgaris was present. Comparisons o f 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 kleptopa rasites. Simultaneous current meter data showed that the movement of A. vul garis and B. undatum to sites where L. polaris was feeding on S. polynyma w as upstream, suggesting chemodetection of food odours. Crabs in the vicinit y may also use visual cues. Leptasterias polaris is the only carnivore that can efficiently extract large clams from the sediments and therefore its f oraging may supply a substantial part of the diet of kleptoparasites. (C) 2 000 The Association for the Study of Animal Behaviour.