Role of Macrofaunal Communities in the Vistula River Plume, the Baltic Sea-Bioturbation and Bioirrigation Potential.

Macrozoobenthos plays a key role in the transformation of inputs from rivers to the sea, such as nutrients, organic matter, or pollutants, and influences biogeochemical processes in the sediments through bioturbation and bioirrigation activity. The purpose of our study was to determine the structure of benthic communities, their bioturbation (BP) and bioirrigation potential (IP), and the vertical distribution of macrofauna in the Gulf of Gdańsk. The study revealed changes in the structure of benthic communities and, consequently, in the bioturbation and bioirrigation potential in the study area. Despite the presence of diverse and rich communities in the coastal zone, BP and IP values, although high, were formed by a few species. Both indices were formed mainly by the clam and polychaetes, although the proportion of polychaetes in IP was higher than in BP. In the deepest zones, the communities became poorer until they eventually disappeared, along with all macrofaunal functions. Both indices changed similarly with distance from the Vistula River mouth, and there was a very strong correlation between them. We also demonstrated that the highest diversity of the macrofauna was observed in the upper first cm of the sediment, but the highest biomass was observed in deeper layers-at a depth of up to 6 cm, and single individuals occurred even below 10 cm.