Coastal eutrophication phenomena in the eastern Gulf of Finland

Macroalgae blooms and consequent oxygen depletion are temporal and spatial large-scale effects of eutrophication that can influence negatively on benthic fauna. The biomass dynamics of the algae Cladophora glomerata was studied in shallow-water littoral zone of the Neva estuary during May-October of 2003-2005. Also, mean production rate, biomass contribution of drifting C. glomerata and oxygen conditions in habitats were examined during algae decomposition. Two peaks in C. glomerata biomass, in July and in September, were found in all studied years with maximum (300plusmn100 g DW m^-2) in September. Primary production of C. glomerata varied from 3.6 to 7.9 contributing around 90% in total production rate in this zone. During decomposition (since the middle of July to late August) the biomass of drifting C. glomerata exceeded the biomass of the attached algae, contributing 62% of total algal biomass in studied area. The depletion in oxygen content in water near the bottom was recorded in the shallow-water zone to 20-m distance from shoreline. This phenomenon can influence negatively on invertebrate communities in shallow-water habitats, facilitating their structural shifts.