Epifaunal communities on Baltic upper circalittoral coarse sediment and shell gravel

This is a Baltic Sea benthic habitat in the aphotic zone where at least 90% of the substrate is coarse sediment or shell gravel according to the HELCOM HUB classification. Sessile/semi-sessile epibenthic bivalves/epibenthic chordates cover at least 10% of the seabed and more than other perennial attached erect groups. The habitat typically occurs below 20m and is mostly encountered in high energy exposure areas. In offshore areas shell gravel bottoms are mainly found permanently at the same location whereas closer inshore they are more likely to shift dynamically from one location to another.

Six associated biotopes have been described; ‘Baltic aphotic shell gravel dominated by epibenthic bivalves (AB.E1E) where there is one sub-habitat with a large representation (at least 50% of the biomass) of Mytilidae’ (AB.E1E1) and ‘Baltic photic shell gravel characterised by epibenthic chordates (AB.E1F) with a sub-habitat dominated by vase tunicate (Ciona intestinalis) (AB.E1F1)'. The latter, which is only, present in the Belt Sea, occurs in areas where the bottom consists largely of mollusc shells or small shell fragments, often in small patches along with other sediments. Due to the combination of the extended interstitial space and the presence of biotic hard substrates, it is inhabited by a unique combination of endobenthic and epibenthic species, such as the vase tunicate (Ciona intestinalis). In these habitats coverage of epibenthic chordates is at least 10% of the sea floor, of which vase tunicate (Ciona intestinalis), which is largely annual in the Baltic, often constitutes at least 50% of the biomass. The tunicates might be overgrown by Ectocarpus spp. or Desmarestia spp. during summer in the photic zone. 

There are also associated aphotic shell gravel and coarse sediment biotopes characterised by mixed epibenthic communities (AB.I1V & AB.E1V) by epibenthic bivalves (AB.I1E) and shell gravel characterisied by a sparse epibenthic macrocommunities (AB.E2T).

Indicators of quality: 

Both biotic and abiotic indicators have been used to describe marine habitat quality. These include: the presence of characteristic species as well as those which are sensitive to the pressures the habitat may face; water quality parameters; levels of exposure to particular pressure, and more integrated indices which describe habitat structure and function, such as trophic index, or successional stages of development in habitats that have a natural cycle of change over time. There are no commonly agreed indicators of quality for this habitat, although particular parameters may have been set in certain situations e.g. protected features within Natura 2000 sites, where reference values have been determined and applied on a location-specific basis. Diversity, abundance and biomass of the dominant. species and associated fauna are potential indicators of quality of this habitat

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats