Copepods attain high abundance, biomass and production in the absence of large predators but suffer cannibalistic loss

Zooplankton samples were collected at intervals of 3–5 days for a year in Fukuyama Harbor, a eutrophic inlet of the Inland Sea of Japan, using a 62-μm-mesh plankton net. The copepod community, which consisted of twelve species, had a very high abundance, biomass and production rate. Acartia omorii, Centropages abdominalis, Oithona davisae and Paracalanus sp. were the most abundant species. The annual average abundance and biomass of adults and copepodites were 1.10×105 ind. m−3 and 39.1 mg C m−3, respectively, one of the highest values so far reported in coastal marine waters. The annual average production rate was 6.85 mg C m−3 d−1, of which Paracalanus sp., O. davisae, A. omorii and C. abdominalis accounted for 27, 26, 25 and 13%, respectively. The combination of an abundant food supply and scarce large predators, except for the ctenophore Bolinopsis mikado which was abundant only in mid-summer, allowed the high abundance, biomass and production of copepods. However, predation on copepod eggs and early nauplii by adults and late copepodites reduced the population recruitment rate and copepod production.