Abstract

In the Upper Pettaquamscutt River Estuary (UPR) and the Upper Point Judith Pond (UPJP), Rhode Island, the main forage fish are the silversides Menidia menidia and Menidia beryllina. The zooplankton communities in the UPR and UPJP are quite different, especially in spring when these two species ripen for spawning. The zooplankton community at UPR is dominated by calanoid copepods, suggesting a rather clean environment, whereas that at UPJP is dominated by polychaete larvae, suggesting a somewhat degraded environment. We study the effect of zooplankton composition, i.e., food quality, on the provisioning of the two species for reproduction and on reproductive success. We measured proximate composition and concentrations of essential fatty acids (EFAs) in the zooplankton food of Menidia species, their eviscerated carcasses, gonads, and the eggs they produce to trace the biochemical composition of prey to offspring. We also monitor weights of gonadal and somatic tissues, egg volume, percent hatch and larval length at hatch. For proximate composition, significant differences were only observed in lipids a) for zooplankton between estuaries, b) between Menidia spp., and c) between estuaries for each Menidia species. For fatty acids, significant differences were only observed in the ?n3, ?n6 and ?n9 fatty acids for zooplankton and for M. menidia gonads between estuaries. Despite the observed biochemical differences, no significant differences were found in unfertilized egg volume or % hatch between estuaries for either Menidia spp.; however, length at hatch for M. menidia at UPJP was significantly greater than that at UPR.

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