EFFECTS OF IMPOUNDING COASTAL SALT-MARSH FOR MOSQUITO-CONTROL ON MICROCRUSTACEAN POPULATIONS

Populations of microcrustaceans were studied for 24 months in two New Jersey high salt marsh impoundments, and in three separate 14 month st udies of high salt marsh pools in northeastern Massachusetts. In Massa chusetts high marsh pools, dominants were all harpacticoids: Amphiascu s pallidus, Cletocamptus deitersi, Harpacticus chelifer, Mesochra lill jeborgii, Metis jousseaumei, and Nitokra lacustris. The cyclopoids Apo cyclops spartinus, Halicyclops sp. and the calanoid Eurytemora affinis were also numerically important. While there was extensive overlap, d ominants varied to some extent from year to year and among the three s tudies. The New Jersey saline impoundment fauna showed extreme dominan ce (low equitability) in the first summer, somewhat less in the second and much less in the third. Total microcrustacean densities also decl ined each year. Variation in Apocyclops spartinus densities was the ma jor factor, as this species comprised in three consecutive summers, 95 , 85 and 51% of the total zooplankton at one station. Diversity as spe cies richness was highest in a New Jersey freshwater impoundment which compared well with South Carolina salt marsh values. Impoundment dive rsity which was very low, and comparable with that found in a New Jers ey Spartina patens marsh, increased each year becoming progressively m ore like that found in the Massachusetts pools. Vegetation changed sig nificantly in the New Jersey impoundments over the three years. Sparti na patens died-off in the first summer, while S. alterniflora graduall y declined each year. A visit to the site twenty years later showed al l emergent vegetation to be gone. These successional zooplankton and v egetation changes, together with the possible consequences of interrup ted marsh-bay exchanges should be considered before undertaking any co astal mosquito control involving permanent flooding.