Occurrence and predation by Mnemiopsis leidyi in Barnegat Bay, New Jersey

Abstract

A late-May seed population of the ctenophore, Mnemiposis leidyi, monitored by net tow at four stations, increased from an average 0.15 m⁻³ to 68 m⁻³ in 15 days. This increase was coupled with almost complete removal of the adult copepod population, and a general depression of net zooplankton biomass. In eight days following peak density the ctenophore population had declined to 21.9 m⁻³, 32% of its peak level. Oscillations in ctenophore and zooplankton density suggested an equilibrium process toward late June.

With zooplankton biomass as dependent variable, data on the ctenophore population, taxonomic composition of the zooplankton and hydrography were subjected to multiple regression analysis. Calculated zooplankton biomass agreed closely with the observed means. Log₁₀ ctenophore abundance, a measure of predator pressure, produced the greatest reduction in unexplained variation (0.01<P<0.025). The recruitment of bottom invertebrate larvae into the plankton was next most important (0.01<P<0.025). Plankton data from other years suggests this dynamic predatorprey interaction is an annual event in this barrier built estuary which is an excellent site to study the phenomenon because of a low flushing rate and the absence of ctenophore predators.