Top-Down Impacts of Sea Nettles (Chrysaora quinquecirrha) on Pelagic Community Structure in Barnegat Bay, New Jersey, U.S.A.

Coastal communities are substantially affected by human activities and create environments conducive to opportunistic species and structural changes in food webs. The Mid-Atlantic coast of the United States is highly urbanized with significant landscape modification and elevated pollutant loads. The appearance and development of resident populations of the Atlantic sea nettle (Chrysaora quinquecirrha) in Barnegat Bay, New Jersey demonstrates a successful establishment to this estuary. This research indicates that two species of gelatinous zooplankton (Mnemiopsis leidyi, C. quinquecirrha) play important structuring roles in the pelagic community. Specifically, M. leidyi exerts significant top-down control of calanoid copepods, cladocerans, fish eggs, and fish larvae, whereas C. quinquecirrha's impact is felt through control of M. leidyi, whose density is two orders of magnitude greater. It was expected that if C. quinquecirrha exerted top-down control of M. leidyi, then a trophic cascade would result. However, no trophic cascade was observed, as C. quinquecirrha demonstrated broad control of pelagic community structure as a nonspecific, generalist predator. Consequently, the strength of M. leidyi's ability to exert predation pressure is mediated by the development of the C. quinquecirrha bloom, but pelagic community structure is broadly defined by the combined impact of these predators within the system.