Temperature effects on predation of juvenile sea scallops [Placopecten magellanicus (Gmelin)] by sea stars (Asterias vulgaris Verrill) and crabs (Cancer irroratus Say)

Predation of juvenile sea scallops Placopecten magellanicus by sea stars Asterias vulgaris (80-100 mm diameter) and crabs Cancer irroratus (80-98 mm carapace width) was examined in the laboratory at different seawater temperatures. Prey sizes used were those demonstrated previously to be preferentially consumed by the respective predators. Consumption rate of small (5-9 mm shell height, SH) scallops by sea stars was not significantly different at 4° and 8 °C, but was significantly higher at 15 ° C (Q₁₀ = 6.9). Similarly, consumption rate of large (19-23 mm SH) scallops by crabs was not significantly different at 3 ° and 8 ° C, but was significantly higher at 15 ° C (Q₁₀ = 2.1). Increased predator activity, as indicated by increased time spent searching for prey, increased predator searching movement velocities (which, for sea stars, resulted in increased encounter rates with scallops), and shorter prey handling times, explained part of the increased predation rate by sea stars and most of that by crabs. Predation rate by sea stars also increased with temperature because of decreased effectiveness of the scallops' escape response, as evidenced by a significantly higher probability of capture upon encounter at 15 °C than at 4° and 8 ° C, although the probability of sea stars capturing scallops was very low (< 0.1) at all experimental temperatures. The probability of crabs capturing encountered scallops was higher (> 0.3) and independent of temperature. The probability of sea stars and crabs consuming captured scallops was ~ 1 and temperature independent.