The importance of small-sized copepods in a frontal area of the Aegean Sea

Distribution, production and grazing of the copepod community were investigated in the northern Aegean Sea, which is characterized by a permanent thermohaline front. Cruises were conducted along a transect crossing the frontal area during spring and late summer. Biomass and production of autotrophs were measured by size fractionation and heterotrophic nanoflagellates and ciliates were also studied. Copepod biomass, production and grazing impact on the phytoplankton and ciliate populations were estimated. The copepod community was sampled with a 45 mu m net to include the smallest species and their developmental stages. The size, structure and distribution of the phytoplankton imply that most carbon was fixed by picoplankton during both seasons and throughout the study area. The partitioning of carbon among the different plankton compartments was not a broad-based pyramid and the biomass of heterotrophs was higher than that of autotrophs, except in the non-frontal region during spring. Copepod biomass was substantially higher in the frontal area. Our results showed that the small-sized copepods (calanoids and cyclopoids) dominated in terms of biomass and production, but also had a greater influence on the efficiency of the trophic coupling between the primary producers and the protozooplankton than the larger species, stressing their importance in the northern Aegean Sea and the Eastern Mediterranean in general.