WILLIAMS, R. L.*; JOHNSON, K. B.; University of South Florida; Florida Institute of Technology: Seasonal Variation, Diet and Prey Selection of the Ctenophore Mnemiopsis leidyi in a Subtropical Estuary

Published studies suggest mechanisms controlling blooms of the ctenophore Mnemiopsis leidyi vary relative to latitude and, in some estuaries, their presence reduces zooplankton standing stocks. It has been proposed that, in temperate estuaries, temperature controls the ctenophore�s presence, while food availability has more influence in estuaries of the Gulf of Mexico. We examined abundance, diet and prey selectivity of M. leidyi in a subtropical estuary on the eastern coast of central Florida. The Indian River Lagoon (IRL) holds an intermediate position relative to estuaries where M. leidyi blooms have been mainly studied; we hypothesized patterns of bloom control and ecological effects would be intermediate as well. Replicated plankton tows were collected weekly for one year, and twice weekly when M. leidyi was present, to sample the zooplankton community and quantify potential prey. Separate tows were used to determine M. leidyi abundance; to conduct gut content analysis, ctenophores were collected individually while submerged in situ. Prey for which M. leidyi displayed the strongest preference were pollen, juvenile flatworms, barnacle nauplii and bivalve veligers. In contrast, protists, polychaete metatrochophores, and copepod nauplii were generally selected against. M. leidyi were present in the study area from January to March and neither temperature nor food availability controlled the timing or size of the bloom. Examination of size class data reveals the ctenophore population likely did not originate in the waters of the study site, but was instead transported from a neighboring �nursery� site. The mechanisms of control behind M. leidyi blooms in this intermediate subtropical estuary do not cleanly fit the proposed latitudinal patterns.