Mussel beds on Pontic circalittoral terrigenous muds
|Red List habitat type||code BLSA5.62|
|Source||European Red List habitat factsheet|
|European Red List of habitats reports|
|European Red List of habitats (Excel table)|
This habitat is comprised of mixed circalittoral sediments – terrigenous muds - mixed with variable amounts of recent or subfossil shells, most of them belonging to the blue mussel Mytilus galloprovincialis, occurring offshore, between depths of 20 and 45 m. At these depths environmental conditions are relatively constant year-round: low light, low temperature (6-9°C), and a constant salinity of 18 ppt. Mytilus galloprovincialis forms biogenic reefs through the accumulation of mussel shells in time and aggregation of the shells by byssal threads. Over time, a hard substratum higher than the surrounding sediment is formed, on which living mussel colonies attach themselves. The reef is formed of numerous elongated patches and/or continuous ridges, always transverse to the prevailing bottom currents (which bring food to the filter-feeders). Between these lay the organic-rich “Mytilus mud” formed by accumulation of mussels’ faeces and pseudofaeces. The biomass of Mytilus galloprovincialis may vary between 200 and 1,500 g/m2.
Among the habitats which occur on sedimentary substratum in the Black Sea, the mussel beds have the highest biodiversity, due to both extending through a wide range of depths and to providing a multitude of microhabitats suitable for a large number of species. This biogenic reef is unique through the crucial ecological role played by the great biofiltration power of the mussel beds in, which ensures the benthic-pelagic coupling and provides enhanced ecosystem resilience. The ‘mussel mud’ formed by the blue mussels’ waste is an important source of food for deposit-feeding infauna living in the sediment around the mussel beds.
The high- biodiversity mussel beds harbour various threatened species and have socio-economical importance as a habitat (breeding grounds, nurseries) and fishing area for commercially valuable species (Psetta maeotica, Squalus acanthias, sturgeons, Rapana venosa). Mussels themselves are the most popular mollusc species for human consumption around the Black Sea, and mussel beds are a source of larvae and spat for aquaculture. The habitat is present all around the coasts of Bulgaria, Romania, Ukraine, Russia and Georgia as a discontinuous belt at variable depths between 20 and 45-80 m. Historically the habitat used to be present in front of the Turkish coast as well, but was completely destroyed due to intensive bottom trawling during the last 100 years.
Indicators of quality:
Biomass, density and cover are some of potential indicators of quality for this habitat. In Romania the following thresholds have been established:
-Reduced habitat fragmentation – the area of enclaves of Melinna palmata muds occurring inside the habitat ≤10.5%
-Cover of living mussels inside patches ≥50%
-Median shell length of living Mytilus galloprovincialis inside patches ≥50 mm.
-Live biomass of Mytilus galloprovincialis ≥5,000 g/m2
In Russia and Ukraine the average biomass of macrozoobenthos in 1970-1980 was more than 450 g/m2, with a density of 350 ind/m2. Now some decline in the number and biomass is observed. In different regions average biomass varied from 220 to 300 g/m2, and density 250-270 ind/m2. Off the coast of Crimea average density and biomass of macrozoobenthos in the habitat were quite uneven as we can see from different authors: 3,700 ind/m2 and 59 g/m2, respectively and 844 ind/m2 and 227.7 g/m2, respectively.
Synthesis of Red List assessment
There are data limitations which impact the reliability of the assessment. These relate to: current extent of habitats, lack of quantitative quality data and data gaps for Turkey. Quantitative data on habitat quantity and quality are available for Romania, Bulgaria, Ukraine, Crimea and Russia but expert opinion has also been used for this assessment.
Althought this habitat has a large EOO and AOO, and therefore qualifies as Least Concern under criterion B, the habitat is assessed as Endangered both at the EU 28 and EU 28+ levels because of the extent of decline in both quality and quanity over the last 50 years.
|Red List Category||Red List Criteria|
|Red List Category||Red List Criteria|
Confidence in the assessment
Pressures and threats
- Biological resource use other than agriculture & forestry
- Professional active fishing
- Nutrient enrichment (N, P, organic matter)
- Natural System modifications
- Siltation rate changes, dumping, depositing of dredged deposits
Habitat restoration potential
Trends in extent
Average current trend in quantity
Trends in quality
Average current trend in quality
Conservation and management needs
List of conservation and management needs
- Measures related to marine habitats
- Other marine-related measures
- Measures related to spatial planning
- Establish protected areas/sites
- Legal protection of habitats and species
- Measures related to hunting, taking and fishing and species management
- Regulation/Management of fishery in marine and brackish systems
- Measures related to special resouce use
- Regulating/Managing exploitation of natural resources on sea
Geographic occurrence and trends
|Seas||Present or presence uncertain||Current area of habitat (Km2)||Recent trend in quantity (last 50 years)||Recent trend in quality (last 50 years)|
Extent of Occurrence, Area of Occupancy and habitat area
|Extent of Occurrence (EOO) (Km2)||Area of Occupancy (AOO)||Current estimated Total Area||Comment|
|EU28||32,603||128||Unknown||No accurate data available for the present extent of the habitat. Older data is available (e.g. Bulgaria) but extent is known to have been reduced by trawling activities so cannot be relied upon.|
|EU28+||340||Unknown||No accurate data available for the present extent of the habitat. Older data is available (e.g. Bulgaria) but extent is known to have been reduced by trawling activities so cannot be relied upon.|
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).
Relation to other habitat types mentioned in legal instruments
|Legal text||Annex||Name in legal text||Code in legal text||
|Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora - consolidated version 01/01/2007||Annex I: natural habitat types of community interest whose conservation requires the designation of special areas of conservation||Reefs||1170||Narrower||http://ec.europa.eu/environm...rective/index_en.htm|