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The zebra mussel Dreissena polymorpha, a ponto-caspian byssate bivalve, forms permanent dense populations along the shoreline in the northern part of the inner Neva Estuary. Its total biomass along a 17 km transect reached 4980 tons (mean 1060 g m-2) in 2000 and 6510 tons (mean 1385 g m-2) in 2001. Being persistent and abundant, the zebra mussel populations played an important role in benthic–pelagic coupling in inner Neva River Estuary. The D. polymorpha population released up to 514 kg day-1 of dissolved inorganic phosphorus and was, therefore, a major source of bioavailable nutrients in the area. Mussel beds were also efficient biofilters and precipitate 15,020 kg day-1 of particulate organic matter during the warm season. About 50% of precipitated matter had a relatively long retention time, being utilized within zebra mussel populations, while the rest was deposited as faeces and pseudofaeces and served as a source for organic pollution to the eastern Gulf of Finland. [Copyright &y& Elsevier]

Ecosystem studies in the littoral zone of the Neva estuary have shown that eutrophication is a serious environmental problem for the coastal zone of the eastern part of the Gulf of Finland. It brings about an intensive development of filamentous algae Cladophora gloinerata and periodical blue-green blooms. Wave action detaches Cladophora mats from substrates and causes an intensive secondary pollution of the beaches in the St. Petersburg Resort District. The zoobenthos community is dominated by caddis fly larvae in the shallow littoral. The alien species Dreissena polymorpha in deeper littoral is facilitating filamentous algae growth, clearing the water and recycling nutrients. An important recovery measure in the ecosystem management in the coastal zone is removal of hard substrates from shallow waters to curb the development of filamentous algae. Another important measure is nutrients reduction and control of the P : N ratio in the coastal zone of the Gulf of Finland. [ABSTRACT FROM AUTHOR]

We analyzed hydrology, geology and benthic species composition to determine benthic habitat distribution patterns in a geologically complex area of the Gulf of Finland, Northern Baltic Sea. The analysis included several datasets describing coastal influence and geodiversity at multiple spatial scales. Geodiversity in this context refers to variation and/or patchiness of benthic substrates and seabed features. Multivariate statistical methods including BEST and LINKTREE routines were used to identify correlative relationships between different ecological variables. Environmental variables (e.g. water depth, Secchi depth, salinity) were either measured by sampling and remote sensing methods or parameterized from geographic and oceanographic data. Benthic assemblages were assayed by both video recordings and zoobenthic sampling (benthic grabs). Statistical analyses identified correlations between benthic datasets and environmental variables, but correlation parameters were not consistent especially with respect to differing zoobenthic and video-based estimates of benthic diversity. The ratio of Secchi depth to water depth showed strong correlation with species distributions observed in video recordings (ρ = 0.56) whereas variables describing broad-scale geodiversity and archipelago gradient (the abundance of islands, ratio of land and sea area) correlated with zoobenthic sample data (generally ρ > 0.30). A model that included independent variables of Secchi depth and terrain roughness within a 20 km radius explained the greatest proportion of spatial variation in zoobenthic sample data (ρ = 0.69). Secchi depth and roughness values were positively correlated with species richness. We designated nine benthic marine landscapes on the basis of these two variables. Linkage tree statistical analysis (LINKTREE) routine utilized zoobenthic sample data as these offered better regional coverage and therefore effectively tracked relationships with other environmental variables. The benthic marine landscapes found in topographically complex seabed areas possessed higher species diversity than flatter areas with fewer seabed features. Our results indicate that on broad spatial scales, geodiversity and archipelago gradient directly influence benthic assemblages by providing a range of different habitats. These factors also indirectly influence benthic assemblages by channeling water movement and thereby distributing hydrologic conditions. This study demonstrates that broad-scale geodiversity should be considered in regional and mesoscale habitat mapping, maritime spatial planning and conservation policies. [ABSTRACT FROM AUTHOR]