Due to its unique salinity gradient and high variability in habitat types, the Baltic Sea contains a greater biodiversity and variety of plant and animal life than might be expected. However, growing pressures (described in Chapter 4) in recent decades have taken their toll on the species. Achieving a good status of the biodiversity in the long term is a HELCOM priority, strengthened by the revised Helsinki Convention in 1992. The latest results show that many species are still under threat. It is anticipated that biodiversity will show signs of improvement in the coming years, as the effects of recently implemented measures is being seen, but also that continued efforts to support biodiversity are of key importance.
The Baltic Sea is home to about 2 700 macroscopic species and innumerable smaller microscopic species (HELCOM 2012, 2013b). Around 1 700 macroscopic species are found in the most marine sub-basin of the Baltic Sea, the Kattegat, while only around 300 species occur in the most freshwater-influenced area, the Bothnian Bay, reflecting the effect of low salinity on the distribution of many species of marine origin (Figure 5.0.1, see also Figure 1.2).
The goal of the Baltic Sea Action Plan is to reach a favourable conservation status of Baltic Sea biodiversity. HELCOM Recommendations are important regional agreements for achieving this goal. For example, HELCOM countries have agreed to take measures to improve the status of species that are threatened according to the 2013 HELCOM Red List (HELCOM 2013b) with the aim of achieving a favourable conservation status for all species by 2021 (HELCOM 2016h). Marine Protected Areas (MPAs) are important tools to conserve both species and habitats in the Baltic Sea, expressed through a HELCOM Recommendation to establish an ecologically coherent and effectively managed network of HELCOM MPAs (HELCOM 2014b).
This biodiversity assessment builds on work over many years in HELCOM to develop core indicators to evaluate the status of important species and species groups, including their abundance, distribution, productivity, or physiological and demographic characteristics (HELCOM 2013c). Hithertoregionally agreed biodiversity core indicators have been made operational and are included in this assessment, and additionally three are agreed to be included as test. The assessment is a milestone in this continuous development, with the long term aim of HELCOM countries being to incrementally improve the regional assessment by including more aspects of biodiversity.
While the biodiversity assessment has been considerably strengthened since the initial holistic assessment (HELCOM 2010a) there is still room for improvement through the inclusion of additional features. For example, the current assessment does not encompass the condition of habitats and biotopes, and only one HELCOM core indicator, on zooplankton, is representing the plankton community. Developments are ongoing in HELCOM in this regard and new core indicators may be ready by 2018.
This chapter presents core indicator results for biodiversity components representing functional groups from secondary producers up to apex predators. The indicators assess all key taxonomic groups occurring in the Baltic Sea (Figure 5.0.2), based on available data.
The integrated biodiversity assessment has been carried out using the integrated biodiversity assessment tool (BEAT) for the level of five ecosystem components; benthic habitats, pelagic habitats, fish, mammals, and water birds (Supplementary 2017E). In the integrated assessment, the biodiversity core indicators have been supplemented with additional indicators, with the aim of achieving a regionally representative assessment that is as comprehensive as possible. Selected core indicators of eutrophication have been added to the biodiversity assessment in cases where no directly corresponding biodiversity indicators are yet available. In coastal areas, national indicators have also been used. Information on commercial fish were obtained from the International Council for Exploration of the Sea (ICES; see also Chapter 4.6 Species removal by fishing and hunting).
Descriptions of the core indicators are found in the core indicator reports (HELCOM 2017k, w-ag, see also HELCOM 2017g-j), and a method description for the integrated assessment of biodiversity is found in the supplementary report (HELCOM 2017E).