Food limitation of production by adult Acartia tonsa in Narragansett Bay, Rhode Island1

Abstract

Egg production, dry weight, cephalothorax length, and condition factor were measured for adult Acartia tonsa females collected twice weekly from Narragansett Bay, R.I., during summer 1979 and incubated in ambient bay water and in ambient bay water enriched with laboratory‐cultured algae. Egg production, dry weight, and condition factor of copepods in the ambient bay water fluctuated considerably (ranges 1.6–51.6 eggs·female‒1·d‒1, 7.37–16.60 µ g dry wt, and 1.09–2.37 condition factor) and closely followed the seasonal trends in Chl a and particulate carbon and nitrogen. Cephalothorax length remained fairly constant during the study. The overall mean egg production rate, dry weight, and cephalothorax length of the copepods after incubation for 48 h in the algae‐enriched water were significantly greater than for copepods incubated in ambient bay water (mean values 45.9 vs. 25.3 eggs·female‒1·d‒1, 13.2 vs. 11.8 µ g dry wt, and 901.7 vs. 891.8 µ m long). Since body size and egg production in adult A. tonsa responded rapidly to a change in food availability, the copepods must have been continuously food limited in Narragansett Bay during summer.