Red List of Biotopes and Habitats

A Red List threat assessment was made for 209 biotopes of which 59 were red-listed. Of the assessed biotopes, 73% were classified LC and are therefore currently not seen to be at risk of collapse.

Only one biotope was categorized in the most severe threat category CR, the biotope delineated by aphotic muddy bottoms dominated by the ocean quahog (Arctica islandica) mussel. The Red List assessment results indicate that many of the threatened biotopes occur in the deep areas of the Baltic Sea. The reason for most of these biotopes becoming threatened is eutrophication, indirectly causing oxygen depletion in the deep areas. Many of the deep biotopes occurring on soft sediments have declined due to destructive fishing methods such as bottom trawling. Furthermore, many of the red-listed biotopes occur in the southwestern Baltic Sea due to the salinity restricted distribution of the species that are characteristic of the biotope.

Data availability is relatively poor for many biotopes and long time series are generally lacking. Therefore the threat assessment is supported by expert judgement. The confidence in the threat assessment is described as High (H), Medium (M) or Low (L).

The assessment methodology is described in detail in the BSEP138 Red List of Baltic Sea underwater biotopes, habitats and biotope complexes.