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Summary
A comparative analysis was carried out of reproductive mode, larval development pattern, and larval growth rate under identical conditions of three members of the Capitella capitata species complex: Capitella sp I from New York, US, Capitella sp M from shallow hydrothermal vents off Milos, Greece, and Capitella sp S from an intertidal flat on Sylt, Germany. In addition, three populations from salmon farms, Capitella K (Kilmelford, Scotland), Capitella Cm and Capitella Ct (Cranford, Ireland), are described for the first time. Three development patterns were observed: planktotrophic (Capitella K and Ct populations), lecithotrophic (Capitella spp I, M and Cm populations), and direct development (Capitella sp S). Experiments with planktotrophic larvae from the Capitella K population at different temperatures, in the presence and absence of light and with several kinds of substrate were not successful in inducing settlement, although differences in the duration of larval survival were observed. Overall, major differences in reproductive modes and larval development patterns were observed among representatives of different species and populations reared under identical culture conditions. In contrast, such modes and patterns are consistent across generations. Whereas larval type and developmental mode appear to be determined largely by genetic factors, environmental conditions have an important influence on the timing of key developmental processes, such as settling and growth.