Effects of sediment amended with sewage, algae, or hydrocarbons on growth and reproduction in two opportunistic polychaetes

Abstract

The effects of organic- (sewage and blue-green algae) and hydrocarbon- (no. 2 fuel oil) amended sediments on growth schedules, age and size at maturity, fecundity, and reproductive output were examined for the opportunistic polychaetes Streblospio benedicti Webster and Capitella sp. I. The two species responded very differently to the amended sediments. For S. benedicti, asymptotic size was reduced and age at first reproduction occurred later in the algae and hydrocarbon treatments compared to the marsh mud only and sewage treatments. Organic- and hydrocarbon- amendedsediments did not affect per brood measures of fecundity or C and N investment in S. benedicti. In contrast, Capitella sp. I exhibited strong, positive responses to the organically amended sediments; this was seen in terms of more rapid growth (2 × ), younger age at first reproduction (50%), larger asymptotic size (6 × ), and higher per brood fecundity and C and N investment (4 × ). Reproductive output, a relative measure of reproductive investment, was not directly affected by treatments in either species. For Capitella sp. I in organically enriched settings, the benefits of larger body size appear to include higher per brood fecundity without increasing the relative cost (in terms of reproductive output) of producing a brood of young. The population explosions of Capitella sp. I in response to organic enrichment are the result of earlier reproduction and increased body size and fecundity. Positive population-level responses of S. benedicti to contaminated sediments may be the result of its ability to tolerate conditions that other members of a community do not.