What is the status of benthic invertebrate communities in the open Baltic Sea?

Key message 

The benthic invertebrate community of the entire Baltic Proper, from the Bornholm Basin to the northern Baltic Proper and the Gulf of Finland, was in a severely disturbed state during the period 2003-2007.

The status of benthic invertebrate communities was good in the Bothnian Sea and the Bothnian Bay.

Figure: Status of benthic inverterate communities in the open sea areas of the Balitc Sea during the period 2003-2007. The interpolated map has been produced in three steps: 1) the status of coastal assessment units has been interpolated along the shores, 2) the status of open sea basins have been interpolated and 3) the coastal and open interpolations have been combined using a smoothing function. The larger circles indicate the status of open sea assessment units and the smaller circles that of the coastal assessment units.

Policy relevance

The composition of animal communities living on the sea bed of the Baltic Sea reflects the conditions of the environment.

In the eutrophication process, broad-scale changes in the composition of the communities – usually involving reduced biodiversity – accompany the increasing organic enrichment of the sediments. At advanced stages of eutrophication, oxygen depletion becomes common.

In many areas of the Baltic, the benthic animals are exposed to widespread oxygen depletion. In areas with periodic oxygen depletion (every late summer and autumn), the number of benthic species is reduced significantly and mature communities cannot develop.

Oxygen depletion may be viewed as a temporal and spatial mosaic of disturbance that results in the loss of habitats, reductions in biodiversity, and a loss of functionally important species. In a Baltic-wide perspective, these disturbances have also resulted in a reduction in the connectivity of populations and communities, which impairs recovery potential and threatens ecosystem resilience. Recovery of benthic communities is scale-dependent and an increase in the extent or intensity of hypoxic disturbance may dramatically reduce rates of recovery.

It is evident that reductions in the distribution and diversity of benthic macrofauna, owing to hypoxic events, have severely altered the way benthic ecosystems contribute to ecosystem processes in the Baltic Sea.

Author(s) and institutions

Alf Norkko and Anna Villnäs - Finnish Environment Institute (SYKE), Finland

References

Andersen, J.H., P. Axe, H. Backer, J. Carstensen, U. Claussen, V. Fleming-Lehtinen, M. Järvinen, H. Kaartokallio, S. Knuuttila, S. Korpinen, M. Laamanen, E. Lysiak-Pastuszak, G. Martin, F. Møhlenberg, C. Murray, G. Nausch, A. Norkko, & A. Villnäs. 2010. Getting the measure of eutrophication in the Baltic Sea: towards improved assessment principles and methods. Biogeochemistry. DOI: 10.1007/s10533-010-9508-4.

HELCOM 2009a. Eutrophication in the Baltic Sea. An integrated thematic assessment of the effects of nutrient enrichment in the Baltic Sea region. Baltic Sea Environment Proceedings No. 115B.

HELCOM 2009b. Biodiversity in the Baltic Sea. An integrated thematic assessment on biodiversity and nature conservationin the Baltic Sea. Baltic Sea Environment Proceedings No. 116B.

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Last updated 5 May 2010