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Marine Habitat Classification


5 results for 'SS.SMp.Mrl.Pcal'

   SS.SMp.Mrl.Pcal  Phymatolithon calcareum maerl beds in infralittoral clean gravel or coarse sand

Maerl beds characterised by Phymatolithon calcareum in gravels and sands. Associated epiphytes may include algae such as Dictyota dichotoma, Halarachnion ligulatum, Metacallophyllis laciniata, Cryptopleura ramosa, Vertebrata byssoides and Plocamium cartilagineum. Algal species may be anchored to the maerl or to dead bivalve shells amongst the maerl. Polychaetes, such as Chaetopterus variopedatus, Lanice conchilega, Psamathe fusca, Mediomastus fragilis, Chone duneri, Metaphoxus fultoni, and Grania may be present. Gastropods such as Steromphala cineraria, Gibbula magus, Calyptraea chinensis, Dikoleps nitens and Onoba aculeus may also be present. Liocarcinus depurator and Liocarcinus corrugatus are often present, although they may be under-recorded; it would seem likely that robust infaunal bivalves such as Circomphalus casina, Mya truncata, Dosinia exoleta and other venerid bivalves are more widespread than available data currently suggests. It seems likely that stable wave-sheltered maerl beds with low currents may be separable from SS.SMp.Mrl.Pcal; having a generally thinner layer of maerl overlying a sandy/muddy substratum with a diverse cover of epiphytes (e.g. Bosence 1976; Blunden et al. 1977; 1981; Davies & Hall-Spencer 1996) but insufficient data currently exists on a national scale. Wave and current-exposed maerl beds, where thicker depths of maerl accumulate, frequently occur as waves and ridge/furrows arrangements (see Bosence 1976; Blunden et al. 1977; 1981; Irvine & Chamberlain 1994; Hall-Spencer 1995). At some sites where SS.SMp.Mrl.Pcal occurs, there may be significant patches of maerl gravel containing the rare burrowing anemone Halcampoides purpureus; this may be a separate biotope, but insufficient data exists at present. Northern maerl beds in the UK do not appear to contain L. corallioides but in south-west England and Ireland L. corallioides may occur to some extent in SS.SMp.Mrl.Pcal as well as SS.SMp.Mrl.Lcor, where it dominates.

   SS.SMp.Mrl.Pcal.Nmix  Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand

Lower infralittoral maerl beds characterised by Phymatolithon calcareum in gravels and sand with a variety of associated echinoderms. The echinoderm Neopentadactyla mixta is frequently observed in this biotope. Other echinoderms such as Echinus esculentus, Ophiura albida and rarely Luidia ciliaris may also be present. Red seaweed such as Plocamium cartilagineum may be present but at a much lower abundance than in SS.SMp.Mrl.Pcal.R and with fewer species present. Other, more ubiquitous echinoderms such as Asterias rubens may also be found in low numbers throughout SS.SMp.Mrl.Pcal biotopes.

   SS.SMp.Mrl.Pcal.R  Phymatolithon calcareum maerl beds with red seaweeds in shallow infralittoral clean gravel or coarse sand

Upper infralittoral maerl beds characterised by Phymatolithon calcareum in gravels and sand with a wide variety of associated red seaweeds. These algae typically include Dictyota dichotoma, Plocamium cartilagineum, Phycodrys rubens, Chondrus crispus, Halarachnion ligulatum, Chylocladia verticillata, Hypoglossum hypoglossoides and Nitophyllum punctum. These species are not restricted to maerl beds but their abundance on maerl beds differentiates this biotope from SS.SMp.Mrl.Pcal.Nmix. Anthozoans and echinoderms are much less common in this biotope than in SS.SMp.Mrl.Pcal.Nmix, which typically occurs deeper than SS.SMp.Mrl.Pcal.R.

   SS.SMp.Mrl  Maerl beds

Beds of maerl in coarse clean sediments of gravels and clean sands, which occur either on the open coast or in tide-swept channels of marine inlets (the latter often stony). In fully marine conditions the dominant maerl is typically Phymatolithon calcareum (SS.SMp.Mrl.Pcal), whilst under variable salinity conditions in some sea lochs beds of Lithothamnion glaciale (SS.SMp.Mrl.Lgla) may develop.

   SS.SMp.Mrl.Lcor  Lithothamnion corallioides maerl beds on infralittoral muddy gravel

Live maerl beds in sheltered, silty conditions which are dominated by Lithothamnion corallioides with a variety of foliose and filamentous seaweeds. Live maerl is at least common but there may be noticeable amounts of dead maerl gravel and pebbles. Other species of maerl, such as Phymatolithon calcareum and Phymatolithon purpureum, may also occur as a less abundant component. Species of seaweed such as Dictyota dichotoma, Halarachnion ligulatum. and Ulva spp. are often present, although are not restricted to this biotope, whereas Dudresnaya verticillata tends not to occur on other types of maerl beds. The anemones Anemonia viridis and Cerianthus lloydii, the polychaetes Notomastus latericeus and Caulleriella alata, the isopod Janira maculosa and the bivalve Hiatella arctica are typically found in SS.SMp.Mrl.Lcor where as Echinus esculentus tends to occur more in other types of maerl. The seaweeds Saccharina latissima and Chorda filum may also be present in some habitats. SS.SMp.Mrl.Lcor has a south-western distribution in Britain and Ireland. Sheltered, stable, fully saline maerl beds in the north of Great Britain (where L. corallioides has not been confirmed to occur) may need to be described as an analogous biotope to SS.SMp.Mrl.Lcor (see SS.SMp.Mrl.Pcal).
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