ZOOPLANKTON ABUNDANCE AND DISTRIBUTION IN TIDAL MARSHES IMPOUNDED FOR MOSQUITO CONTROL

Impounded marshes under different reconnection plans (open vs. RIM) were examined at the culverts and within the interior perimeter ditch to determine if the flow regime influenced the availability of zooplankton. Management plans had no effect on zooplankton abundance, but a significant effect was found with the location within the perimeter ditch, with culverts having a higher overall abundance compared to interior points. The six most abundant taxa, in declining order of abundance, were juvenile flatworms, copepods, nauplii, rotifers, gastropod veligers, and nematodes. Specifically, juvenile flatworms, copepods, nauplii, and nematodes were more abundant at culverts. Dye diffusion studies revealed that areas with the lowest flow rates always had the highest species diversity and 'Evenness' was always higher in the interior of perimeter ditches. Impoundments appear to have the highest zooplankton densities recorded in the literature for any habitat. Canonical Correspondence Analysis of environmental data suggests that different water masses (coastal vs. estuarine) may distinguish the impoundments and drive species differences, while flow into an impoundment is correlated with zooplankton diversity and abundance. We hypothesize that zooplankton may accumulate within the impoundment ditches via migration behaviors (e.g., "selective tidal stream transport").