Influence of benthic invertebrates on phosphorus flux at the sediment-water interface in the easternmost Baltic Sea

ABSTRACT: Since the late 2000s, 2 sediment-dwelling invertebrates, the polychaete Marenzelleria arctia and the oligochaete Tubificoides pseudogaster, have established populations in the Gulf of Finland (Baltic Sea). This article focuses on the effects of these and other benthic species on sediment-water phosphate flux in the easternmost part of the gulf. We estimated total phosphate (soluble reactive form, P-PO43-) fluxes (Pflux), the benthic biomass in intact sediment cores and the phosphate excretion (Pexc) by abundant benthic animals at 4 sites ranging in depth from 20–50 m in the gulf during the Catamaran ‘Centaurus-II’ cruise in August 2015. We found significant positive correlations between Pexc and benthic biomass (especially M. arctia and Monoporeia affinis) and negative correlations between Pflux and benthic variables (biomass and abundance). Pflux in intact sediment-water cores containing various benthic animals ranged from -2890 to +1180 μmol m-2 d-1. Mass-specific Pexc in M. arctia was at least 4 times higher than in other species (Limecola balthica, Saduria entomon, M. affinis and T. pseudogaster). Total benthic excretion rates varied from 320 to 3460 μmol m-2 d-1; 79–98% of which was released by M. arctia. This work reveals a direct effect of benthic animals (via excretion) on phosphate dynamics at the sediment-water interface in the marine environment.