The pelagic ecosystem of the Black Sea goes gelatinous

Abstract

ABSTRACT Following up on the issue of worldwide growing gelatinous plankton dominance, we analysed historical records on zooplankton biomass from the 1970s to the present, in order to assess the ratio of gelatinous- to-non-gelatinous zooplankton (GN). The latter is poorly analysed in current publications featuring the Black Sea pelagic ecosystem. The GN characterizes the quality of zooplankton as a food source for small pelagic fishes which dominate Black Sea fishery. The retrospective analysis of zooplankton biomass constituents in coastal and open sea waters retrieved from published papers was complemented by an 11-year sampling (up until 2021), across the Crimean shelf. The comparison over regions (represented by the north-eastern, the northern, the north-western, the southern and the open sea) showed that the jellyfish Aurelia aurita, the ctenophore Mnemiopsis leidyi, and the dinoflagellate Noctiluca scintillans act as major contributors to the total gelatinous biomass of the 2000s, on a basin scale. On average, the wet gelatinous biomass is about one hundred times that of the non-gelatinous one. High values of the GN ratio (in wet mass and in carbon units) in coastal waters indirectly imply a leading role of a detritus pathway of organic matter in a pelagic ecosystem.