Water Salinity and Benthic Macrophyte Communities Are the Key Variables Defining the Distribution Pattern of Benthic Faunal Assemblages in the Shallow Water Areas of the Gulf of Riga

The distribution of shallow water macrozoobenthic assemblages of the Gulf of Riga is analysed in relation to water current velocity, salinity, sediment type, ice disturbance, eutrophication, and benthic macrophytes. Salinity and benthic macrophyte communities described most of the variability in both the abundance and biomass structure of benthic invertebrates. In addition, surface chlorophyll a also contributed to the variability of benthic invertebrate biomass. Benthic invertebrate assemblages in the vicinity of the Daugava and Parnu rivers experience higher nutrient loading and were therefore characterized by a lower species number and higher biomass of benthic suspension feeders. Benthic invertebrate communities in other regions of the Gulf of Riga were typical for the mildly disturbed areas of the northern Baltic Sea. Compared to the situation in the 1960s, no substantial increase in the abundance and biomass values of macrozoobenthos was observed as could be expected from the basinwide trend of increasing eutrophication.