Behavioural mechanisms of sea stars ( Asterias vulgaris Verrill and Leptasterias polaris Müller) and crabs ( Cancer irroratus Say and Hyas araneus Linnaeus) preying on juvenile sea scallops ( Placopecten magellanicus (Gmelin)), and procedural effects of scallop tethering

Abstract

We compared predation rates and behaviours of sea stars ( Asterias vulgaris and Leptasterias polaris) and crabs ( Cancer irroratus and Hyas araneus) preying on juvenile sea scallops ( Placopecten magellanicus, 25-35 mm shell height) in laboratory. These predatory species co-occur with sea scallops on the sea bed of the Gulf of St. Lawrence, Canada, and limit scallop survival in seeding operations. We also examined, under controlled conditions, the effect of tethering scallops on predator–prey interactions. Predation rates, time budgets and encounter behaviours observed for A. vulgaris and C. irroratus preying on free (untethered) scallops were comparable to previous studies. C. irroratus were more effective predators as they consumed 3.1 scallops predator − 1 day − 1 , although they spent only 0.9% of their time searching for prey. A. vulgaris consumed 0.9 scallops predator − 1 day − 1 and spent 7.6% of their time searching. Sea stars L. polaris had a lower predation rate (0.02 scallop predator − 1 day − 1 ) than A. vulgaris. The frequent avoidance behaviour of L. polaris and its low ability to capture scallops support the notion that scallops are not a main component of this sea star's diet. Crabs H. araneus had similar predation rates (1.3 scallops predator − 1 day − 1 ) and behaviours to C. irroratus, although the probability of consumption upon capture was affected by relatively high numbers of rejections and post-capture escapes of scallops. As expected, the tethering procedure increased predation rate of L. polaris (about 19 times higher), but surprisingly did not significantly affect that of A. vulgaris. Examination of behaviours indicated that A. vulgaris offered tethered scallops tended to have a higher probability of capture, but spent less time searching for prey (possibly because satiation was reached) than A. vulgaris offered free scallops. Predation rates and behaviours of both crab species were not affected by tethering, since encounter rate was the primary determinant of crab-scallop interactions. Identification and quantification of behaviours underlying the predation process allowed us to mathematically model predator-related mortality for the four predator species.