AbstractThe population dynamics and production ofAcartia clausii, a planktonic marine copepod, were studied during 1973 and 1974 in a small temperate lagoon. An approach which integrated laboratory andin situexperiments with time‐series sampling of the field population was used to analyze seasonal changes in the parameters of population growth (development, growth, fecundity, and mortality) and to elucidate the processes which affect these changes. The objective of the study was to understand the factors which control the seasonal cycle of abundance.The cycles of abundance were similar in the two years of study and were not affected by differences in the cycles of tidal inflow, temperature, and food availability even though the latter two factors appreciably affected growth, development, and fecundity rates. The abundance cycle is controlled by an annually consistent pattern of copepodid and adult mortality believed to be due to predation by the three‐spined stickleback, the dominant fish species in the lagoon. Cannibalism and periodic tidal stimulation of hatching of accumulated eggs in the sediment help to regulate population abundance within seasonal limits.Production by the lagoon population was 229 kg C for the entire study period; 84—88% of the annual production occurred from April through July. In the area of the lagoon greater than 3‐m deep the mean daily productions during the peak months of each year were 70 and 55 mg C m−2for 1973 and 1974, res