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Biodiversity & Conservation

Substratum or habitat types

The substratum and habitat types defined below are categories that may support distinctive biotopes or that certain species favour or are characteristic of. Definitions from Hiscock (1996) or Connor et al. (2004) unless otherwise specified.

Substrata
Artificial E.g. wood, metal or concrete structures.
Bedrock Any stable hard substratum, not separated into boulders or smaller sediment units. Includes soft rock-types such as chalk, peat and clay.
Large to very large boulders >512 mm. Likely to be stable.
Small boulders 256 - 512 mm. May be unstable.
Cobbles 64 -256 mm. May be rounded to flat. Substrata that are predominantly cobbles.
Pebbles 16 -64 mm. May be rounded to flat. Substrata that are predominantly pebbles.
Gravel / shingle 4 -16 mm. Clean stone or shell gravel including dead maerl. >80% gravel.
Sandy gravel 50 -80% gravel, 20 -50% sand.
Muddy gravel 50 -80% gravel, 20 - 50% mud.
Muddy sandy gravel 50 -80% gravel, 20 -50% mud and sand
Coarse clean sand 0.5 - 4 mm. > 80% sand.
Fine clean sand 0.063 -0.5 mm. >80% sand.
Gravelley sand 50 -80% sand, 20 -80% gravel.
Muddy gravelly sand 50 -80% sand, 20 -50% mud and sand
Muddy sand 50 -80% sand, 20 -50% mud.
Sandy mud 50 -80% mud, 20 -50% sand.
Sandy gravelly mud 50 -80% mud, 20 -50% sand and gravel.
Gravelly mud 50 -80% mud, 20 -50% gravel.
Mud <0.063 mm (silt / clay fraction). >80% mud.
Clay 1) Sediment particles less than 0.004 mm in size (Wentworth, 1922). 2) A soft very fine-grained sedimentary rock composed primarily of clay-sized particles.
Mixed Mixtures of a variety of sediment types, composed of pebble / gravel / sand / mud. This category includes muddy gravels, muddy sandy gravels, gravelly muds, and muddy gravelly sands.
Habitat types
Algae Macroalgae surfaces, such as Laminaria spp., or fucoids.
Biogenic reef An elevated structure on the seabed built by calcareous or other concretion-forming organisms, or by chemical precipitation (Hiscock, 1996), for example by Modiolus modiolus or Sabellaria alveolata.
Caves A large hollow in the side of a vertical rock face or cliff.
Crevices / fissures Narrow openings (Thompson, 1995).
Maerl Live maerl. Phymatolithon calcareum and Lithothamnion corallioides in Britain and Ireland.
Other species The surface of other species, e.g. shells or carapace.
Overhangs An overhanging part of a rock formation (Thompson, 1995).
Rockpools A pool of water among rocks left behind by the ebbing tide.
Salt marsh A flat, poorly drained coastal swamp inundated by most high tides (Lincoln et al., 1998).
Seagrass Habitat associated with seagrass bed communities.
Strandline A line on the shore composing debris deposited by a receding tide; commonly used to denote the line of debris at the level of extreme high water (Lincoln et al., 1998).
Under boulders Habitat associated with the underside of boulders.
Water column Pelagic.

References