Growth and development in the subtropical copepod Acrocalanus gibber

Abstract

Growth rates of the subtropical copepod Acrocalanus gibber were measured in field incubations. Prosome length of adult females was correlated with rearing temperature, but variation in condition of copepods masked any correlation of temperature with carbon and nitrogen content. The resulting N-specific growth rates (GN) were log-linear and ranged from 0.49 to 0.72 d-1 at temperatures of 24.4-29.2°C. Highest growth rates occurred in the middle of the temperature range, but no relationship between GN and temperature could be established, although molting rate and generation time were correlated with temperature. Growth rate was negatively related to chlorophyll a concentration and was independent of paniculate C and N. Nitrogen-specific egg production, measured either from wild-caught females or from females produced in the incubations, never exceeded 0.28 d-1 (representing only 46% of GN) and was frequently near zero. In this respect, juvenile growth was less food-limited than was adult growth (measured as egg production). The measured duration of A. gibber developmental stages, particularly copepodite stages 1 and 5, varied in laboratory experiments, apparently as a result of variation in food composition. Molting rate, copepod weight, and the resulting growth rates appear to be influenced by food quality.