Larval performance in an estuarine crab, Chasmagnathus granulata; is a consequence of both larval and embryonic experience

摘要

In an experimental laboratory investigation on an estuarine crab, Chasmagnathus granulata Dana, we investigated how salinities experienced during embryonic and larval development (embryonic and larval salinity exposures, respectively) and intraspecific variability of initial biomass at egg laying and hatching affected larval performance. The latter was measured in terms of survival rate, duration of development through successive stages, frequency of occurrence of an additional (fifth) zoeal stage, and size of the first juvenile instar. Ovigerous female crabs were maintained at 3 salinities (15, 20, 32per thousand). For each egg mass, biomass of freshly laid eggs and of freshly hatched larvae, respectively, was measured as dry mass, carbon, and nitrogen contents. After hatching, the larvae were reared at salinities of 5, 10, 15, and 32per thousand. When larvae hatched from eggs that had been incubated at reduced salinities (15 or 20per thousand), their survival through the zoea I stage at low salinities (5 and 10per thousand) was high and stage duration was short. By contrast, poor survival and delayed development were observed in larvae reared at low salinities when they hatched from eggs that had been incubated in full-strength seawater (32per thousand). Larval rearing in seawater allowed generally for highest survival and shortest development. While the embryonic salinity exposure had a strong influence on the performance of the first zoeal stage, later stages showed no significant response to the previous conditions of egg incubation. At advanced stages, low larval salinity exposure (15per thousand) led to consistently lower survival, longer duration of development, and higher proportion of larvae passing through an additional zoeal instar. However, larger juveniles metamorphosed from larvae that hatched from eggs incubated at low (15per thousand) salinity. The initial biomass of eggs and larvae, which varied significantly among broods produced by different females, was identified as another factor affecting larval performance. At constant 32 %o, larvae with high initial biomass showed higher survival and faster development. Significantly more larvae developed through an additional instar when they hatched with a low initial biomass. In conclusion, our results show that the performance in a given phase of a complex life-history depends not only on the present environmental conditions but also on those prevailing in the preceding phase. Moreover, intraspecific variability in maternal energy investment into offspring production may play a significant role for the chances of larval survival and development in the plankton.