In the Bothnian Bay, eutrophication levels and phytoplankton productivity are lower than in the Baltic Sea in general. These bird populations have severely decreased in the Baltic during the last 20 years. Reasons for this include protection schemes, declined concentrations of hazardous substances in prey and sea water, along with improved prey abundance due to over-fishing of large predatory fish(Herrmann et al., As a consequence, an increase in hypoxia-tolerant species has been observed, most notably a dramatic increase in the abundance of the invasive species Marenzelleria spp. (