Harmful Algal Blooms in Coastal Waters of the South-Eastern Baltic Sea

Abstract

Increased nutrient input results in an enhanced production of organic matter (eutrophication) especially in the river plumes of the Baltic Sea. Therefore, the open sea and the near-shore coastal waters are significantly different with regard to nutrient (N, P) and chlorophyll a concentrations, phytoplankton biomass and Secchi depth. Also, the composition of the phytoplankton changes along the river plumes corresponding to the salinity gradient. Therefore, blooms of toxic species can be restricted either to the open sea (e.g. Nodularia spumigena) or to coastal waters (e.g. Microcystis sp.). Lists of potentially toxic species, toxic effects and incidents in the Baltic Sea are given. Toxic blooms not only harm man and animals but also have high economic relevance for mariculture (fish and shellfish farming) and tourism. A surveillance system is established in many countries to protect people from toxic bathing water or seafood. The spreading of non-indigenous species may also introduce new toxic species into the ecosystems. A specific control of toxic blooms or immigration of new species is almost impossible. The most effective measure for reducing algal blooms is combating eutrophication.