Collaborative Research: Initiation and Maintenance of Population Maxima of the Ctenophore Mnemiopsis leidyi in Northern Coastal Waters

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Initiation and Maintenance of Population Maxima of the Ctenophore Mnemiopsis leidyi in Northern Coastal WatersSubstantial increases in peak concentrations of the ctenophore Mnemiopsis leidyi have occurred in the last decade in Narragansett Bay, an estuary at the northern boundary of the geographic distribution of this species. The seasonal timing of Mnemiopsis pulses has also shifted from late summer to early spring during years with earlier warming of bay water temperatures. Significant ecological consequences of this temporal introduction are potentially great. Mnemiopsis is now abundant during the peak period of fish spawning in the region. Severely depleted stocks of zooplankton have been observed in spring and summer of 2000. Similar changes in seasonality and abundance of the species are likely to be occurring in other estuaries in the northeast. Despite the clear ecological importance of large pulses of ctenophores, the quantitative basis for understanding conditions giving rise to rapid population increases is limited. While temperature and food supply must ultimately be dominant variables controlling growth and reproduction of this species, there is little information about reproduction of over-wintering populations or conditionswhich favor growth of larvae in spring. In this study the investigators will conduct field and laboratory studies of Mnemiopsis over the full annual cycle to determine effects of temperature, food supply and food quality on reproductive rates and larval growth. The role of microzooplankton, addressed in only two previous laboratory studies will be fully addressed in both field and laboratory components. Areas of Narragansett Bay which have recently been observed to sustain unexpectedly large population of Mnemiopsis in winter, as well as areas in which populations pulses are delayed until spring will be compared. Hydrographic data will be collected and examined for both direct and indirect effects of physical factors on population growth, including the role of thermal stratification in population pulse initiation. Given the evidence for disruptive effects on ecosystems of seasonal or geographic invasions of Mnemiopis leidyi and the limited number of studies of this species at the northern edge of its geographic range, justification for this study is compelling. Quantitative information on the influence of temperature and food on both larval and adult M. leidyi at the level of detail collected in this study will significantly advance our understanding of factors required for initiation and maintenance of population pulses of this species.