Red List habitat classification > RL - Marine habitats > RLBLS - Black Sea > BLSA5.62 Mussel beds on Pontic circalittoral terrigenous muds

Mussel beds on Pontic circalittoral terrigenous muds

Quick facts

Red List habitat type code BLSA5.62
Threat status
Europe Endangered
EU Endangered
Relation to
Source European Red List habitat factsheet
European Red List of habitats reports
European Red List of habitats (Excel table)

Summary

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.

Characteristic species
For full habitat description, please download the habitat factsheet.

Threat status

Synthesis of Red List assessment

This habitat is known to have almost completly covered the north-west shelf of the Black Sea between 20-60m depth, where the substrate was suitable, prior to 1965. The mussel population, and consequently the extent of this habtat has since suffered a major reduction (more than 50%) , primarily due to the effects of eutrophication. A very substantial decline in quality has also occurred over the last 50 years, estimated as an intermediate decline affecting more than 80% of the habitat.
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.
EU
Red List Category Red List Criteria
Endangered A1, C/D1
Europe
Red List Category Red List Criteria
Endangered A1,

Confidence in the assessment

medium
Red List of habitat categories and criteria descriptions

Pressures and threats

  • Biological resource use other than agriculture & forestry
    • Professional active fishing
  • Pollution
    • Nutrient enrichment (N, P, organic matter)
  • Natural System modifications
    • Siltation rate changes, dumping, depositing of dredged deposits

Habitat restoration potential

No direct intervention actions are appropriate. However, improvement can be made using passive intervention (i.e. legislation). Natural recovery is possible. However, recovery to original extent will be slow due to large area previously covered by the habitat.

Trends in extent

Average current trend in quantity

Increasing Increasing
EU28 EU28+

Trends in quality

Average current trend in quality

Increasing Increasing
EU28 EU28+

Conservation and management needs

Much of the remaining habitat is within Marine Protected Areas but there are few conservation measures within these at present. River inputs are being managed in order to improve the water quality of the Black Sea. For EU states this is archived via the Water Framework Directive (WFD). Desired measures for the future include a ban bottom trawling across the Black Sea and regulations surrounding ballast control, water quality control for Turkey (especially Istanbul), and non-EU Black Sea states.

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

Distribution

For each habitat a distribution map was produced from a wide variety of sources indicating known and potential occurrences of the habitat in 10x10 km grids within Europe. Occurrences in grid cells were given in two classes: actual distribution from relatively reliable sources (surveys, expert knowledge), and potential distribution based on models or less reliable indicators. Please download the fact sheet to see the map.

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)
Black Sea Present Unknown Decreasing Decreasing

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.
AOO = the area occupied by a habitat measured in number of 10x10 km grid cells.
EOO = the area (km2) of the envelope around all occurrences of a habitat (calculated by a minimum convex polygon).

Characteristic species

The full list of characteristic species and genus are available above from the Summary. The species available in the EUNIS database are shown here.
Fishes Acipenser gueldenstaedti
Fishes Huso huso
Fishes Mesogobius batrachocephalus
Fishes Psetta maeotica
Fishes Raja clavata
Fishes Squalus acanthias
Invertebrates Abra alba
Invertebrates Ampelisca diadema
Invertebrates Amphiura stepanovi
Invertebrates Aonides paucibranchiata
Invertebrates Ascidiella aspersa
Invertebrates Calyptraea chinensis
Invertebrates Capitella capitata
Invertebrates Ciona intestinalis
Invertebrates Eumida sanguinea
Invertebrates Glycera alba
Invertebrates Gouldia minima
Invertebrates Heteromastus filiformis
Invertebrates Lepidochitona cinerea
Invertebrates Leptosynapta inhaerens
Invertebrates Melinna palmata
Invertebrates Mytilus galloprovincialis
Invertebrates Nassarius nitidus
Invertebrates Nephtys hombergii
Invertebrates Nereiphylla rubiginosa
Invertebrates Orchomene humilis
Invertebrates Pectinaria koreni
Invertebrates Pitar rudis
Invertebrates Polycirrus jubatus
Invertebrates Pomatoceros triqueter
Invertebrates Rapana venosa
Species scientific name English common name Species group
Acipenser gueldenstaedti Fishes
Huso huso Beluga Fishes
Mesogobius batrachocephalus Knout goby Fishes
Psetta maeotica Fishes
Raja clavata Maiden ray Fishes
Squalus acanthias Blue dog Fishes
Abra alba Invertebrates
Ampelisca diadema Invertebrates
Amphiura stepanovi Invertebrates
Aonides paucibranchiata Invertebrates
Ascidiella aspersa Invertebrates
Calyptraea chinensis Invertebrates
Capitella capitata Invertebrates
Ciona intestinalis Invertebrates
Eumida sanguinea Invertebrates
Glycera alba Invertebrates
Gouldia minima Invertebrates
Heteromastus filiformis Invertebrates
Lepidochitona cinerea Invertebrates
Leptosynapta inhaerens Invertebrates
Melinna palmata Invertebrates
Mytilus galloprovincialis Invertebrates
Nassarius nitidus Invertebrates
Nephtys hombergii Invertebrates
Nereiphylla rubiginosa Invertebrates
Orchomene humilis Invertebrates
Pectinaria koreni Invertebrates
Pitar rudis Invertebrates
Polycirrus jubatus Invertebrates
Pomatoceros triqueter Invertebrates
Rapana venosa Invertebrates

Vegetation types

Relation to vegetation types (syntaxa)

Not available

Other classifications

Not available
European Environment Agency (EEA)
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