Polychaete/ bivalve-dominated mid-estuarine Atlantic littoral mud

Mid-estuarine shores of fine sediment, mostly in the silt and clay fraction though sandy mud (mostly very fine and fine sand) can also be a component of the substrate. Littoral mud typically forms extensive mudflats, though dry compacted mud can form steep and even vertical structures, particularly at the top of the shore adjacent to saltmarshes. Little oxygen penetrates these cohesive sediments, and an anoxic layer is often present within millimetres of the sediment surface. Most mid-estuarine muddy shores are subject to some freshwater influence, though at some locations more or less fully marine conditions may prevail. This habitat is mainly found along mid-estuarine shores and supports rich communities characterised by polychaetes, bivalves and oligochaetes. The mid-estuarine communities may also be present in sheltered inlets, straits and embayments which are not part of major estuarine systems, though there is usually some freshwater influence.

Indicators of quality:

Many indicators of quality have been used for this habitat with particular parameters 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. Indicators of quality of this habitat are frequently linked to those for the whole estuarine environment and therefore include morphological and physical characteristics, carrying capacity and water quality parameters. For the mudflat itself benthic indices, contaminant levels and productivity are some of the frequently used measures of quality.

Indices developed to assess the ecological status of coastal waters, including estuaries, according to the Water Framework Directive, include physical indicators, water quality indicators and measures of benthic diversity, species richness and abundance. The latter group, which is particularly relevant to benthic habitats, includes a Benthic Quality Index, an Infaunal Trophic Index, a Marine Biotic index based on ecological groups, and the Benthic Opportunistic Polychaetes/Amphipods index.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats