R/P-54

Description:

Objectives: This grant seeks to test the hypothesis that small inlets and creeks along Chesapeake Bay tributaries act as 'reactor vessels' for gelatinous zooplankton species that can control much of plankton dynamics and survival of early life stages of summer breeding fishes in the mesohaline region of the Chesapeake Bay system. If the hypothesis is correct, exchange between these reactor vessels and the mainstem tributaries may strongly influence, and under some circumstances may even control, upper trophic level dynamics in Chesapeake Bay tributaries. Depending on the ingress:export ratio, the breeder-vessel characteristics of these small inlets and upper arms of creeks may allow them to act as nutrient sinks, reducing nutrient export to the mainstem of tributaries, or as sites of seed-populations for consumers that strongly influence trophic dynamics. Year 1 - 2 - Methodology: Field sampling of gelatinous zooplankton and their prey in two linked inlet-subtributary-mainstem tributary systems, lab measurements of ctenophore egg production, and field flow measurements will be used to estimate differences in 1) density of medusae and ctenophores, and 2) ctenophore reproduction and Chrysaora ephyra densities, between small inlets with restricted exchange and the larger subtributaries and mainstem tributaries to which they connect; and 3) estimate exchange of gelatinous zooplankton, including larvae, between small inlets and the larger subtributaries. Year 3 - Methodology: Field sampling of gelatinous zooplankton and their prey in four linked inlet-subtributary-mainstem systems, and lab measurements of ctenophore egg production, were begun in 2003 but needed to be repeated in 2004 because of unusual weather conditions during the first year of this project. This request is for a 1-year funded extension to conduct research proposed for Year 2 of the original proposal. We will examine the potential for transport among different subsystems to determine whether inlets and creeks are likely to be net exporters of gelatinous zooplankton to the mainstem of major tributaries. We will use Tucker trawl samples, diver observations and field flow measurements to estimate the net direction of transport of adult and larval Mnemiopsis leidyi and Chrysaora quinquecirrha between small inlets with restricted exchange, creeks and the mainstem Patuxent River. Data will be used to estimate the direction of net transport of gelatinous zooplankton in 3 inlet-creek-mainstem tributary systems along the Patuxent River. Rationale: The dynamics of mainstem systems may be strongly influenced by processes occurring in shallow inlets and creeks. If this hypothesis is correct, monitoring and modeling may need to incorporate the spatial arrangement and importance of these systems to correctly predict human influence and system response to management actions. Our results should offer guidance on the design of these monitoring programs and models. In addition, different land use practices, nutrient control measures and zoning may be appropriate along the shores of these inlets and creeks than along more open stretches of coastlines.