| dc.description | This study examines the effects of biological and physical factors on predation of juvenile sea scallops (Placopecten magellanicus; 5-28 mm shell height) by two major predators, sea stars (Asterias spp.) and crabs (Cancer irroratus). Predator-prey size laboratory experiments with sea stars (30-150 mm diameter) showed that predation rates increased with increasing sea star size and decreasing scallop size. Preference for small scallops by sea stars was determined by prey vulnerability resulting from differential probabilities of capture upon encounter, even though the probability of capture was $$0.20, since scallops often closed their valves upon encounter with crabs. In laboratory experiments, predation rates on preferred prey sizes increased with water temperature (3-15$\sp\circ$C) with Q$\sb $ values of 6.9 and 2.1 for sea stars and crabs, respectively. The increase in predation rate with temperature was attributable to increased foraging activity of sea stars and crabs, and decreased escape effectiveness of scallops with sea stars. In a field experiment manipulating scallop density, crab predation rate increased with scallop density, but crab density did not, indicating a functional response. Sea star predation rate on scallops was not affected by scallop density. In a series of experiments with different size classes of scallops tethered at different sites and water temperatures (seasons), and in different densities of predators and free-living scallops, the effects of covariates on scallop survival times were assessed using the statistical procedure of survival analysis. Since the tethering technique affected crab and sea star predation differently, the competing causes of scallop mortality were analysed separately. Water temperature, site, and scallop density were the important variables affecting crab predation. There was a significant interaction between temperature and site, such that crab predation on scallops increased with temperature at one site and was independent of temperature at the other site. Predation by crabs also increased with scallop density and, to a lesser extent, with crab density. Water temperature and scallop size were the primary variables affecting sea star predation. Sea star predation on scallops increased with temperature and decreased with scallop size. The results of this study further our understanding of predator-prey interactions in the marine benthic environment as well as suggest options for minimizing predation of scallops by crabs and sea stars in bottom culture operations. | en_US |
