Third Annual Long Island Natural History Conference

































Understanding the role of ctenophores and factors influencing seasonal population blooms in Long Island estuaries

Marianne E. McNamara, Ph.D., Suffolk County Community College Biology Department

Jellyfish have received a lot of attention in recent years. Although a natural predator in our coastal waters, “the blobs of summer”, as one researcher coined them, seem to turn everyone (from swimmers for their painful stings to fisherman for their net-clogging tendencies) against them. The ‘jellies’ better known to scientists as gelatinous zooplankton comprise several distinctive taxa including the cnidarians (true ‘jellyfish’ and siphonophores) and the non-stinging salps and ctenophores (comb jellies). The ctenophore Mnemiopsis leidyi is an ecologically important predator that is capable of exerting significant mortality on the zooplankton community in Long Island estuaries. Here, seasonal population blooms of the ctenophore have increased in magnitude and shifted towards an earlier seasonal maximum over the past two decades. Blooms of M. leidyi are made up of both lobate adults, which feed on mesozooplankton (copepods, larval fish and shellfish) and tentaculate larvae, which depend on microplankton (ciliates and dinoflagellates) for prey. Since larval M. leidyi frequently dominate during ctenophore blooms, the abundance and composition of microplankton may explain the timing and magnitude of their blooms and subsequent recruitment into mesozooplankton-feeding adults. Ctenophore population data were used alongside meso- and microplankton abundances to interpret the top-down predatory impact of M. leidyi on the planktonic community in Great South Bay during 2008 and 2009.

Field data suggested significant top-down control of mesozooplankton and microplankton during peak abundances of adult and larval M. leidyi, respectively. Furthermore, the dramatic reduction of mesozooplankton during peak adult abundance resulted in a cascading effect on microplankton in 2009; correlations between high adult M. leidyi/low mesozooplankton with high microplankton abundances were identified, and preceded the increase in ctenophore larvae. These data suggest that blooms of M. leidyi resultin a feedback system, in which intense feeding activity by adults on mesozooplankton releases certain microplankton taxa from grazing pressure, enhancing prey conditions for larval ctenophores.

Additionally, an examination of ctenophore egg production detected a mismatch between optimum egg production by adults and sufficient microplanktonic prey abundance for larvae, resulting in significantly lower ctenophoredensities in 2008 compared to 2009, when ideal prey conditions for adults and larvae coincided.

Dr. Marianne E. McNamara ( is a faculty member in the biology department at Suffolk County Community College where she teaches oceanography, marine biology and biology. She holds a Masters and Ph. D. in Marine and Atmospheric Science from Stony Brook University, where she specialized in zooplankton ecology. Marianne has spent several months at sea in nearby Long Island waters, as well as the Eastern Tropical Pacific and Antarctica. Her research focuses on the feeding ecology of zooplankton – the often-microscopic, drifting animals – of the marine environment, including gelatinous zooplankton or ‘jellies’.

Marianne is an avid photographer and SCUBA diver, and has served as a naturalist for numerous educational outreach programs on Long Island including the Riverhead Foundation for Marine Research and Preservation, the Ward Melville Heritage Organization and the Coastal Research and Education Society of Long Island. Marianne was awarded the Jerry R. Schubel Graduate Fellowship for her role in transmitting science into forms that are accessible to the public and continues to participate in workshops encouraging the use of improvisation theatre exercises to improve scientific communication with actor Alan Alda.

Ph D. candidate, Marine and Atmospheric Science; Stony Brook University 2013; M.S. Marine and Atmospheric Science; Stony Brook University 2007; B.A. Biology; University of Maine at Machias (1998).