Reproductive biology of four planktonic calanoid copepods, Pleuromamma abdominalis, P. gracilis, P. indica and P. xiphias

抄録

This study examined the reproductive strategies of four Pleuromamma species (P. abdominalis, P. gracilis, P. xiphias and P. indica) in Sagami Bay, Japan. Key reproductive traits, including egg production rates (EPR), and the relationship between body size and egg size, were analyzed to uncover interspecific variability and adaptive strategies. The present result was considered the first species-level report on the egg production rates (EPR) of the genus. Average EPRs were almost the same among the species, i.e., around 20 eggs female⁻¹ d⁻¹. Comparisons of the female body, egg and clutch carbon contents suggest variations in reproductive patterns across species. Among the four species, P. gracilis, the smallest and distributed near the surface of the food-rich environment, produced both the highest egg carbon (1.88% of body carbon) and clutch carbon (43%). Its high egg carbon content corresponded to those of egg-brooding species. Our result implies that the small body size of P. gracilis reduces predation pressure, allowing it to perform diel vertical migration (DVM) over shorter distances near the surface and to invest energy obtained from feeding into its reproduction.