Production of a Calanoid Copepod, Acartia Tonsa, in the Patuxent River Estuary

Acartia tonsa Dana was found to be the most abundant copepod during 7 months of the year in a 10-mile segment of the Patuxent River estuary. Densities up to 100,000 copepods per cubic meter were observed during the warmer months, and as low as 1,500 during the colder months. The summer population was composed mainly of immature stages and the winter population mainly of adults. Production was calculated by dividing population biomass by turnover times. Turnover times were calculated from instantaneous death rates of nauplii and copepodids. Instantaneous death rates were estimated from observed population age structures in the field and development times in containers of estuary water. Growth of A. tonsa from egg to egg required 7, 9, and 13 days at 25.5° C, 22.4° C, and 15.5° C respectively. Production for a 2-month summer period was estimated to be 2.51 to 2.77 mg/ m3 hr. Assuming an average depth of 3 m for the study area, production is 1.61 to 1.78 lb/acre day. In consideration of the possible sources of error the estimates of production are probably somewhat conservative. At least half of the planktonic primary production in the Patuxent estuary is consumed by A. tonsa during the summer months. Production of A. tonsa in the Patuxent estuary compares favorably with the production of herbivorous fish in fertilized ponds.