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Marine Habitat Classification

Description of biotope or habitat type

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   Halichondria bowerbanki, Eudendrium arbuscula and Eucratea loricata on reduced salinity tide-swept circalittoral mixed substrata

Physical habitat description

Salinity Reduced (18-30ppt), Variable (18-35 ppt), Low (<18ppt)
Wave exposure Sheltered, Very sheltered
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock, boulders, cobbles, pebbles
Zone Circalittoral
Depth Band 0-5 m, 5-10 m, 10-20 m
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 CR.MCR.CFaVS.HbowEud <I>Halichondria bowerbanki</I>, <I>Eudendrium arbuscula</I> and <I>Eucratea loricata</I> on reduced salinity tide-swept circalittoral mixed substrata

  • 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'
  • Predicted extent of the level 3 (for sublittoral rock & deep sea) or 4 (for sublittoral sediment) habitat

Point data based on records in the UK Marine Recorder Snapshot. Predicted habitat extent is from UKSeaMap.


This biotope typically occurs on circalittoral mixed substrata (bedrock, boulders, cobbles, pebbles and gravel) in the moderately strong, tide-swept narrows near the entrance of Loch Etive, although not in the extremely tide-swept Falls of Lora. This sea loch is unique in having a substantial freshwater input from the surrounding moorland, yielding the most brackish, large sea loch in Scotland. Large growths of the brackish-tolerant sponge Halichondria bowerbanki cover the cobble and boulder seabed, interspersed with Amphilectus ovulum, the hydroid Eudendrium arbuscula and the bryozoan Alcyonidium diaphanum which are particularly characteristic of these conditions. Tufts of the bryozoan Eucratea loricata are occasional in most areas. Other species recorded include Carcinus maenas, Asterias rubens, Crossaster papposus, Buccinum undatum, Pagurus berhardus, Henricia spp., Onchidoris bilamellata and Palio dubia, tolerant of the low salinity, are found in the circalittoral throughout this area. Ascidians such as Ascidiella scabra and Corella parallelogramma may also be present. A very impoverished low salinity version is present in the upper basin of Loch Etive. The biotope CuSpH is similar in several respects to this biotope and will develop in less brackish situations where species-richness is generally greater.


No situation data available.

Temporal variation

Not known.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Halichondria bowerbanki 16 Occasional 81-100%
Eucratea loricata 15 Frequent 81-100%
Balanus crenatus 12 Frequent 61-80%
Ascidiella scabra 11 Common 61-80%
Corella parallelogramma 9 Occasional 61-80%
Eudendrium arbuscula 7 Frequent 81-100%
Alcyonidium diaphanum 3 Occasional 41-60%
Asterias rubens 3 Occasional 41-60%
Buccinum undatum 3 Occasional 41-60%
Pagurus bernhardus 3 Frequent 41-60%
Amphilectus ovulum 2 Occasional 41-60%
Carcinus maenas 1 Occasional 41-60%
Crossaster papposus 1 Rare 41-60%
Henricia 1 Occasional 21-40%
Onchidoris bilamellata 1 Frequent 21-40%
Palio dubia 1 Occasional 21-40%

Similar biotopes or habitat types

This sub-biotope occurs in very sheltered variable salinity bedrock, subject to moderately strong tidal streams. It is much more impoverished than CR.MCR.CFaVS.HbowEud, lacking the hydroid Eudendrium spp. Also lacks many red algae species.

This sub-biotope occurs in more marine conditions in the outer parts of estuaries. A diverse range of cushion sponges and hydroids are present, unlike CR.MCR.CFaVS.HbowEud.

Classification history of this biotope or habitat type

Classification version Code
2015 (15.03) CR.MCR.CFaVS.HbowEud
1997 (97.06) CR.ECR.BS.HBowEud

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