Sparse or no macrofaunal communities on Baltic infralittoral muddy sediment

This is a Baltic Sea benthic habitat in the photic zone where at least 90% of the substrate is muddy sediment according to the HELCOM HUB classification. It occurs in areas where there is low to medium exposure to wave action. Macrovegetation, epifauna and infauna are generally sparse or absent however the one associated biotope described has a large representation (more than 50% of biomass) of meiofauna. This is ‘Baltic photic muddy sediment dominated by meiofauna (Oligochaeta, Ostracoda, Nematoda)’ (AA.H4U1).

The benthic meiofauna in the Baltic Sea is a diverse group of small animals including Ostracoda, Nematoda, Oligochaeta, Rotifera, Turbellaria and Copepoda living on and in the sediments. In the north-western Baltic Sea Proper, Nematoda are the most abundant group of benthic meiofauna, making up between 67–91% of the species observed in the sediment. Only nematodes are found to be common below 2 cm depth in the sediment. Meiofauna can be split into surface feeders and subsurface feeders. Sedimentation of organic matter may have an effect on the meiofaunal community, as the increased rate of sedimentation can increase the abundance of surface feeding species.

Indicators of quality:

Quality indicators have not been described for this habitat. Generally the ecology of meiofaunal communities is less well understood than that of benthic macrofauna communities. Fewer studies have been carried out and in many studies meiofauna is only stated to be present in a certain abundance. Studies looking into the environmental requirements and species interactions are rare. It is also quite rare that meiofauna is taxonomically identified to species level which is the rule in macrofauna studies. 

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats