Preliminary results of an experimental study of the effects of mysid predation on estuarine zooplankton community structure

In a shallow estuarine system near Beaufort, North Carolina, a period of high winter abundance of the mysidsMysidopsis bigelowi andNeomysis americana was associated with a change in zooplankton species composition, from dominance byAcartia tonsa to dominance byCentropages spp. andSaphirella sp. Both mysids feed onA. tonsa at higher rates than the other copepods. Experiments were carried out in 600–1 000 liter enclosures, in which the initial mysid density was manipulated and the effects on the enclosed copepod community were monitored. Mysid predation had a significant effect on copepod densities. The effects of mysid predation on species composition appeared to depend on the relationship between their prey preferences and the dominant copepod species present in the communities. Under conditions favoring dominance byA. tonsa, the preferred prey species, the results suggested that mysid predation may reduce dominance and increase diversity. But when the less preferredCentropages was dominant, mysid predation had no effect on species composition.