Functional response of midsummer planktonic and benthic communities in the Neva Estuary (Eastern Gulf of Finland) to anthropogenic stress

Long-termhydrobiological research has shown that the functioning of the ecosystem of the Neva Estuary, one of the largest Baltic estuaries, has changed greatly since the beginning of the 20th century. Ineffective local water management in St.Petersburg during the last twenty years has stimulated the development of a natural ‘biological plug’ in the salt barrier zone in the inner part of the estuary and has altered the ecosystem’s functioning. These changes include an increase in primary production, in the primary production : organic matter decomposition ratio, and in pelagic-benthic coupling. It has also given rise to filamentous algae blooms and intensive secondary pollution in the coastal zone of the Neva Estuary. The primary production of phytoplankton in the inner part of the estuary has reached 2.3 gC m−2, that of the filamentous algae Cladophora glomerata 5.5 gC m−2; these figures are much higher than in other regions of the Gulf of Finland.