Baltic offshore circalittoral mud characterized by the polychaetes Scoloplos arminger and where the substrate is predominantly clay Pontoporeia femorata and Terebellides stroemi.

Description (English)

This is a Baltic Sea benthic habitat in the aphotic zone, comprising areas of soft sediment, predominantly mud, below the halocline, typically at depths below 70-100m. The strong permanent halocline and seasonal thermocline in summer limits vertical mixing of the water column leading to the formation of oxygen-depleted zones in the deep areas of the central Baltic. The environmental conditions of the deep zone of the Baltic are not uniform but vary widely in terms of salinity (14-21 ppt) and oxygenation (3-80% saturation). During periods of stagnation, this separation by the halocline gives rise to an oxygen deficit and periodically to complete oxygen depletion and formation of hydrogen sulphide (H2S). In places there is a continuously oxygen poor zone which is virtually devoid of macrofauna and has an extremely impoverished meiofauna generally consisting of a few thousandnematodes per square meter only
Characteristic speceis; .In the deeps around Gotland the polychaetes Scoloplos arminger and where the substrate is predominantly clay Pontoporeia femorata and Terebellides stroemi.

Source: EUNIS habitat classification