We used a mean size-frequency distribution of biomass to estimate the secondary production of the congeneric species assemblage of Acartia in a semi-isolated station in Malaga harbour (SE Spain) during the summerautumn period. Acartia was the dominant copepod in the water column. Co-occurring species were A. clausi, A. grani and A. discaudata var. mediterranea. Biomass values displayed a long period cycle with large amplitude throughout this period. The cycles extended from June to October and the biomass values increased by a factor of 10x at the peak in August. Estimated average production was 13.90 mg dry wt m^-3d^-1 (6.26 mg C m^-3 d^-1). The high concentration of chlorophyll suggests that copepods can always find sufficient food for maximal growth.