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Marine Habitat Classification

Description of biotope or habitat type

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   Polychaete/bivalve-dominated mid estuarine mud shores

Physical habitat description

Salinity Full (30-35 ppt), Reduced (18-30ppt), Variable (18-35 ppt)
Wave exposure Sheltered, Very sheltered, Extremely sheltered
Tidal streams
Substratum Sandy mud, mud
Depth Band Lower shore, Mid shore, Upper shore
Other Features

Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.

Distribution of habitat LS.LMu.MEst Polychaete/bivalve-dominated mid estuarine mud shores

  • Records used to define the biotope (core records)
  • Other records assigned to this biotope, marked as 'certain'
  • Other records assigned to this biotope, marked as 'uncertain'

Point data based on records in the UK Marine Recorder Snapshot.


Mid estuarine shores of fine sediment, mostly in the silt and clay fraction (particle size less than 0.063 mm in diameter), though sandy mud may contain up to 40% sand (mostly very fine and fine sand). 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. Mid estuarine muds support rich communities characterised by polychaetes, bivalves and oligochaetes.


Principally along mid estuarine shores. The mid estuarine communities may also be present in sheltered inlets, straits and embayments which are not part of major estuarine systems, though usually there is some freshwater influence.

Temporal variation

Enteromorpha spp. and Ulva lactuca may form mats on the surface of the mud during the summer months, particularly in areas of nutrient enrichment or where there is significant freshwater influence.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale Typical abundance - (count per m2) % of core records where taxon was recorded
Hediste diversicolor 16 Abundant 899 81-100%
Macoma balthica 15 Common 591 81-100%
Tubificoides benedii 14 Abundant 3690 61-80%
Peringia ulvae 11 Common 3031 61-80%
Pygospio elegans 8 Common 719 61-80%
Streblospio shrubsolii 8 Common 731 61-80%
Eteone longa 3 Abundant 104 41-60%
Nephtys hombergii 3 Common 75 41-60%
Scrobicularia plana 3 Abundant 112 41-60%
Cerastoderma edule 2 Common 132 41-60%
Abra tenuis 2 Common 214 21-40%
Aphelochaeta marioni 2 Abundant 1794 21-40%
Manayunkia aestuarina 2 Common 883 21-40%
Tharyx killariensis 2 Common 429 21-40%
Tubificoides pseudogaster 2 Common 2095 21-40%

Similar biotopes or habitat types

Not applicable or unknown.

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