Regional scale climate forcing of mesozooplankton dynamics in Chesapeake Bay

A 16-yr (1985-2000) time series of calanoid. copepod (Acartia tonsa and Ewyternorv affinis) abundance in the upper Chesapeake Bay was examined for links to winter weather variability. A synthesis of sea level pressure data revealed ten dominant, winter weather patterns. Weather patterns differed in frequency of occurrence as well as associated precipitation and temperature. The two dominant copepod species responded differently to winter weather variability. A. tonsa abundance showed little response to winter weather and did not vary in abundance during wet or dry springs. E. affinis responded strongly to winter weather patterns that produced springs with high freshwater discharge and low salinities. During wet springs, E. affinis abundance increased overall and its area of dominance extended further down estuary. The different response of the two species is likely related to several factors including residence time, development time, salinity tolerance, food limitation, and life history strategy. Important fish species that rely on zooplankton as food resources were also related to winter weather variability and spring zooplankton abundance. Monme saxatihs (striped bass) and Anchoa mitchilli (bay anchovy) juvenile indices were positively and negatively correlated to E. affinis abundance, respectively.