Biodiversity in Enclosed Seas and Artificial Marine Habitats Proceedings of the 39th European Marine Biology Symposium, held in Genoa, Italy, 21-24 July 2004

at deeps where natural periodic low oxygen concentrations make the system highly vulnerable Eutrophication is ranked among the most serious to the load of organic matter (Cloern, 2001; threats to the stability of marine ecosystems HELCOM, 2002; Karlson et al. , 2002). worldwide (Gray et al. , 2002). The effect of Eutrophication has been an increasing ecol- eutrophication is more pronounced in the coastal ical threat in the Baltic Sea during the past areas which receive large amounts of organic and 50 years. During this time the load of nutrients mineral nutrients from municipal wastes, agricul- has grown fourfold for nitrogen and 8 times for tural and industrial ef?uents (Cloern, 2001; Gray phosphorus leading to an increased production at et al. , 2002). In order to protect coastal waters all trophic levels in the ecosystem (Elmgren, most European countries have to implement the 2001). Increasing nutrient concentrations have European Water Framework Directive. Accord- also severely affected macrozoobenthos, being ing to the directive all waterbodies must obtain expressed as the loss of species and increase in good water quality prior to 2015. To implement abundance and biomass (Karlson et al. , 2002). the directive, the reference (i. e. pristine) condi- Due to low salinity and a short geological history, tions and criteria for ecological status need to be relatively few macrobenthic species have adapted de?ned (European Union, 2000).