Estimates of planktonic larval mortality using the marine gastropods Crepidula fornicata and C. plana

Abstract

Estimates of planktonic larval mortality rates have varied widely over the past 50 yr, from about 0 % d-1 to 80 % min-1. Convincing estimates from field sampling programs have proved difficult to obtain. This study considered the impact of predation pressure on larval growth rates for 2 species of the gastropod genus Crepidula whose larvae grow linearly over time. We reasoned that slow-growing larvae should be more vulnerable to predators than fast-growing larvae, so that in the face of substantial predation pressure mean larval growth rates should increase over time, with larger individuals growing on average more rapidly than smaller individuals as the more vulnerable slower growers are preferentially culled from the population. Larvae of C. fornicata and C. plana were collected from the plankton and reared individually in the laboratory under controlled conditions of temperature and food supply; larvae that were large when captured had significantly higher mean growth rates, on average, than those that were small when captured. A computer simulation confirmed that such results are consistent with substantial rates of predation on slow-growing individuals. © Inter-Research 2007.