INSITU FEEDING-BEHAVIOR OF THE COPEPOD TEMORA-LONGICORNIS - EFFECTS OF SEASONAL-CHANGES IN CHLOROPHYLL SIZE FRACTIONS AND FEMALE SIZE

We estimated in situ ingestion rates of females of the calanoid copepod Temora longicornis in Long Island Sound, New York, USA, at roughly weekly intervals, between February and August from 1985 to 1987 using the gut fluorescence technique. Variability in gut pigment content (GPC) and ingestion rates (IR) was examined in relation to changes in the concentration of total chlorophyll and of chlorophyll in the > 20-mu-m size fractions, and changes in body size. Correlations of GPC and IR with chlorophyll concentration were highest for the > 20-mu-m size fraction and lowest for total chlorophyll. Saturation of GPC and IR was apparent only when phytoplankton > 10-mu-m or > 20-mu-m was considered as available food. These results lend support to the notion that the degree to which herbivorous coastal copepods are food-limited may be strongly dependent on the structure of the phytoplankton assemblage. Prosome length of female T. longicornis decreased by almost a factor of 2, and dry weight by a factor of 4, from February to August. Correlations between weight-specific GPC, weight-specific IR and chlorophyll concentration in all size fractions were poorer than in the cases of GPC and IR on a per individual basis. However, a multivariate regression analysis indicated that most of the variance in GPC and IR was explained by the different size fractions of chlorophyll, not body weight. Therefore, the use of weight-specific indices may not always be justified even when variation in body size is pronounced. We suggest that multivariate analysis or other statistical techniques be employed, instead of weight-specific indices, when body size may be a confounding variable.