Phytoplankton species diversity exhibits large year-on-year fluctuations, but no trend over time. However, the number of species varies relatively little when calculated on the Baltic Sea scale, and no temporal trends are still seen here. Overall, the species diversity of phytoplankton cannot be stated as being in good environmental condition, as the data base is currently too insubstantial to be able to assess this.

The data series for the species diversity of zooplankton in the Baltic Sea is based on sampling from one to two stations in the summer. This is not comprehensive for the MRU and does not necessarily give a true and fair view of the species diversity in the area. The number of species varies without a clear trend from 1979 to 2009, after which no data are available.

The total marine mammal biomass is stable or increased from 1994 to 2016. The biomass in 2005 was lower than in 1994 (Figure 23.6). Harbour porpoises make up 82-89% of the biomass all year, and the total figures for marine mammals are therefore mainly controlled by the biomass of harbour porpoises. The spotted seal has increased in number from 1994 to 2005 and from 2005 to 2016 in both areas. Gray seal was virtually absent in 1994 and 2005, but in 2016 the number has increased significantly in the MRU. Furthermore, according to the GES decision, good environmental status for seals and porpoises is considered to correspond to favorable conservation status under the Habitats Directive. The condition of marine mammals in the Danish marine areas was assessed in 2013 under Article 17. It was considered that the condition of the spotted seal in the Baltic Sea and the Great Belt was favorable, while the condition of harbour porpoises and gray seals was unfavorable. Based on that, it is not possible to make an overall assessment of the state of the trophic level.

The overall plankton biomass has been steadily declining in the Baltic Sea and the Great Belt from 1978 to 2016. A slight increase is seen after 2012.

For birds, good environmental status corresponds to the assessment under Article 12 of the Birds Protection Directive. Data from the recent report (2013) of breeding birds shows that, in general, certain species groups are stable or progressive, such as herbivores and birds foraging in the water column. For groups such as waders and birds foraging in the surface, less than 75% of the species are stable or in progress. For wintering birds, most of the species groups are stable, progressive or fluctuating, but not birds that seek food on the seabed.