Connecting export fluxes to plankton food-web efficiency in the Black Sea waters inflowing into the Mediterranean Sea

Abstract

The short-time scale evolution of plankton carbon partitioning and downward flux in the modified Black Sea water (BSW) mass entering the northeast Aegean Sea was studied using a Lagrangian approach (6–10 April 2008). The free-drifting sediment trap positioned at the bottom of the BSW layer and the control drifter, followed the same path within the anticyclone that circulates the BSW in the area. Ζooplankton biomass increased (from 159 to 292 mg C m−2), as did faecal pellet production (from 5 to 8 mg C m−2 day−1), whereas a generally decreasing trend was displayed by particulate organic carbon (POC) (from 2099 to 1440 mg C m−2), net primary production and biomass of plankton cells >5 µm (from 32 to 11 mg C m−2 day−1 and from 153 to 124 mg C m−2, respectively). At the same time, the organic carbon flux increased (from 131 to 311 mg C m−2 day−1), due to the contribution of zooplankton detritus (from 30 to 165 mg C m−2 day−1). Normalized biomass-size spectra slopes suggest an elevated grazing pressure upon microplankton cells and a non-steady-state ecosystem. Moreover, both the overall shallow slope values and their high correlation to organic carbon flux indicate an increased efficiency of energy transfer to higher trophic levels.