ENVIRONMENTAL-REGULATION OF FEEDING AND EGG-PRODUCTION BY ACARTIA-TONSA OFF SOUTHERN CALIFORNIA

The feeding, diet and egg production of the copepod Acartia tonsa were dermined during ten experiments in Los Angeles Harbor, California, between November 1986 and October 1987. Copepods were incubated in situ, in quasi-natural food environments. Water temperatures ranged from 14.6 to 21.5-degrees-C. Particulate organic carbon and nitrogen (POC and PON) were high (534 to 3710-mu-g Cl-1, 51 to 459 Nl-1) but dominated by small (< 8-mu-m diam) particles. Plankton (phytoplankton and microzooplankton) C-biomass composed about 10% of the total POC and was usually dominated by particles > 8-mu-m. Plankton biomass was always low. Daily ingestion rates ranged from 3 to 96% of body C; egg production ranged from 4 to 35 % of body carbon. Mean ingestion and egg production rates during spring-summer were 1.9 and 1.5 times higher than average for the entire study, respectively. The average gross efficiency of egg production for the study was 80%; the spring-summer mean was 41 %. Bivariate and multiple-regression analyses revealed that the ingestion rate was dependent upon both temperature and food availability, but that, below 21-degrees-C, egg production depended more upon temperature than upon food concentration. To detect dietary preferences, the composition of diet was compared with that of the food supply. Selective feeding was infrequent, but the diet was often dominated by dinoflagellates and ciliates. It would appear that within metabolic limits governed by temperature, the feeding response of A. tonsa is dependent upon food concentration, while egg production depends more on qualitative attributes of the food supply.