Estuarine calanoid copepod abundance in relation to season, salinity, and land-derived nitrogen loading, Waquoit Bay, MA

Calanoid copepod abundance and distribution were measured by monthly plankton tows from May through November in 1998 and March through August in 1999 in three subestuaries of the Waquoit Bay estuarine system. There was a dramatic seasonal change in the composition of calanoids in Waquoit Bay with a spring community consisting of Acartia hudsonica, Centropages hamatus, and Eurytemora affinis, replaced by Acartia tonsa in the summer. The abundance of A. hudsonica, A. tonsa, and C. hamatus was higher in the saltier reaches of the subestuaries, but the abundance of E. affinis and copepod nauplii was not affected by salinity. Even though different land-derived nitrogen loads created different concentrations of chlorophyll in the water of Waquoit Bay subestuaries, there was no apparent response in the abundance of most calanoid copepods to differences in nitrogen load to the subestuaries. The uncoupling of phytoplankton food from mesozooplankton consumers suggests that other factors such as water residence time, phytoplankton quality and composition, or variations in microzooplankton food play a role in the abundance dynamics of Waquoit Bay calanoid populations.