Kelp and seaweed communities on Atlantic infralittoral mixed sediment

Shallow sublittoral mixed sediments consisting of hard substrate components (cobbles, pebbles, gravel and shells) in various densities which support seaweed communities, typically including the kelp Saccharina latissima the bootlace weed Chorda filum and various red and brown seaweeds, particularly filamentous types. The environmental conditions also dictate the typical seaweed communities present. In areas where winter storms are common, seaweed cover will be more ephemeral and fragmented, due to high mortality rates from damage and detachment; whilst in more sheltered areas, long term attachment to smaller cobbles/pebbles is possible. Loose mats may be present in the most sheltered environments. The strength of tidal flow and type of substrate also influence the community type.

A diverse array of animals is associated with these kelps and seaweeds, including burrowing polychaete worms and bivalves, scavenging hermit crabs, crabs, starfish, fish and grazing top shells. Kelps and seaweeds growing on sediment greatly increase the primary production of an area and create a more diverse habitat. Gastropods, amphipods, sea urchins and fish graze the seaweeds; starfish, urchins, hermit crabs and crabs are scavengers; crabs and fish are opportunistic predators; and a mixed infauna of deposit feeders and suspension feeders develops, depending on sediment type. Various biotopes have been described associated with this habitat characteristised by Saccharina.latissima, Chorda.filum and red seaweeds on sheltered muddy sediments as well as mats of  Trailliella on muddy gravel  and  loose-lying mats of Phyllophora crispa on muddy sediment.

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. The depth limit of kelp and/or red seaweeds is used in some countries as a Water Framework Directive parameter for assessing ecological status.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats