Marine Atlantic infralittoral fine mud

Shallow sublittoral muds, extending from the extreme lower shore to about 15-20 m depth in fully marine or near marine conditions, predominantly in extremely sheltered areas with very weak tidal currents. Such habitats are found in sealochs and some rias and harbours. In very shallow extremely sheltered very soft muds the lugworm Arenicola marina may form very conspicuous mounds and casts. At such sites, high densities of synaptid holothurians such as Labidoplax media and Leptosynapta bergensis occur. The sediment surfaces may become covered by a diatom film at certain times of the year. Mobile species are opportunistic scavengers and predators and include starfish (e.g. Asterias rubens), crabs and hermit crabs (e.g. Carcinus maenas and Pagurus bernhardus), flatfish and gobies (e.g. Pomatoschistus minutus). 

Sheltered sediments such as these are characterized by fine grain size, low porosity, generally low permeability (and hence high water content), high sediment stability (due to cohesion), a low oxygen content and highly reducing conditions. The mud surface is oxygenated. However, in fine muds, the anoxic reducing layer is likely to be very close to the surface, often less than 1cm. Bioturbation by burrowing species, results in mobilisation of the sediment and nutrients from deeper sediment to the surface, making nutrients available to surface dwelling organisms. In addition, continued irrigation of their burrows by Arenicola marina and Leptosynata sp. transports oxygenated water into the sediment, resulting in oxygenated micro-environments in the vicinity of their burrows.

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 indiceswhich 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. Key driving influences and output processes of shallow sublittoral mud habitats that are likely to be sensitive to pressures and may be useful for monitoring to identify anthropogenic causes of change include habitat structure changes, removal of particular species such as those which are key in bioturbation and biodeposition, or nutrient and biogeochemical cycling, changes in siltation rates and organic enrichment.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats