Science Serving Maryland's Coasts
Edward Houde, Ph.D.
Chesapeake Biological Laboratory
Spatial Distribution of Adult Copepods and Cladocera In and Around the Chesapeake Bay Estuarine Turbidity Maximum
The Estuarine Turbidity Maximum (ETM), located at the head of many estuaries like the Chesapeake Bay, is a region of high turbidity and suspended particle concentrations. The ETM is a nursery area for larval fish and may concentrate zooplankton species. The goal of this study is to determine the spatial distribution of adult copepods and cladocera that are potential prey of fish larvae in and around the Chesapeake Bay ETM in both a wet (1998) and dry (1999) year. Plankton concentrations were analyzed from depth-stratified 1-m2 Tucker-trawl (280 micron mesh) samples that were taken at stations in the channel of the upper Chesapeake Bay. The study focused on the abundant calanoid copepods Eurytemora affinis and Acartia tonsa, and the cyclopoid parasitic copepod Ergasilus labricus. Cladocera analyzed were Bosmina longirostris and Daphnia pulex. Although total zooplankton concentrations were highest within and below the ETM zone in both 1998 and 1999, zooplankton distribution varied between species, year, and depth. Eurytemora and Ergasilus were concentrated in the ETM in 1998, but not in 1999. Acartia was concentrated below the ETM zone, and Cladocera were mostly found above the ETM. Vertical distribution varied among species, and between sexes of the same species. Changes in distribution and abundance of zooplankton in the ETM may have important consequences for higher trophic levels since the distribution of prey and parasitic copepods overlapped and was similar to that of larval striped bass and white perch.
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