Effects of resident species on recruitment into a community larval settlement versus post-settlement mortality in the oyster Crassostrea virginica

Abstract

Laboratory and field experiments revealed that a variety of species of common, sessile invertebrates, including barnacles, ascidians, and bryozoans, affected the settlement and post-settlement abundance of the oyster Crassostrea virginica (Gmelin). While the nature of the effects varied, most species both reduced oyster settlement by covering and removing substrate available for attachment, and increased settlement on adjacent surfaces. The solitary ascidians Ciona intestinalis (L.) and Styela clava (Herdman), were found to be predators of oyster larvae. Post-settlement survivorship and growth were also strongly affected by the presence of sessile species. In most cases the effects were negative and correlated with the abundances of the species. Data suggest that competition for planktonic food was the mostly likely cause of reduced growth and survivorship. For many resident species, the combination of reduced oyster settlement on their own exposed surfaces, increased settlement on substrate adjacent to them, and decreased post-settlement survivorship in theu presence resulted in these species havlng little effect on net recruitment. These results demonstrate the need for distinguish~ng interactions among benthic invertebrate populations during the period from settlement to recruitment.