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Marine Habitat Classification


2 results for 'SS.SSa.IMuSa.SsubNhom'

   SS.SSa.IMuSa.SsubNhom  Spisula subtruncata and Nephtys hombergii in shallow muddy sand

In shallow non-cohesive muddy sands, in fully marine conditions, a community characterised by the bivalve Spisula subtruncata and the polychaete Nephtys hombergii may occur. The sediments in which this community is found may vary with regard to silt content but they generally have less than 20% silt/clay and in some areas may contain a degree of shell debris. This biotope falls somewhere between SS.SSa.IMuSa.FfabMag and SS.SSa.CMuSa.AalbNuc with regard to sediment type (i.e. somewhat muddier than SS.SSa.IMuSa.FfabMag and less muddy than SS.SSa.CMuSa.AalbNuc) and may have species in common with both. As a result, other important species in this community include Abra alba, Fabulina fabula and Kurtiella bidentata. In addition, Diastylis rathkei/typical, Philine aperta (in muddier sediments), Ampelisca spp., Ophiura albida, Phaxas pellucidus and occasionally Bathyporeia spp, may also be important, although this is not clear from the data available. In areas of slightly coarser, less muddy sediment S. solida or S. elliptica may appear occasionally in this biotope. Abundances of Spisula subtruncata in this biotope are often very high and distinguish it from other closely related biotopes. Extensive areas of this community to the north east of the Dogger Bank were recorded in the 1950s, but these seem to have declined since then (Kroncke 1990). More information is required with regard to the status of this biotope.

   SS.SCS.ICS.MoeVen  Moerella spp. with venerid bivalves in infralittoral gravelly sand

Infralittoral medium to coarse sand and gravelly sand which is subject to moderately strong water movement from tidal streams may be characterised by Moerella spp. with the polychaete Glycera lapidum (agg.) and venerid bivalves. Typical species include Asbjornsenia pygmaea or M. donacina with other robust bivalves such as Dosinia lupinus, Timoclea ovata, Goodallia triangularis and Chamelea gallina. Other infauna include nephtyid and spionid polychaetes and amphipod crustacea. Another important component of this biotope in some areas is the bivalve Spisula solida (see Kuehne & Rachnor 1996) which may be common or abundant. In conjunction with SS.SSa.IMuSa.FfabMag this biotope may form part of the 'Shallow Venus Community', the 'Boreal Off-shore Sand Association' and the 'Goniadella-Spisula association' of previous workers (see Petersen 1918; Jones 1951; Thorson 1957; Salzwedel, Rachor & Gerdes 1985). Epifaunal communities may be reduced in this biotope when compared to SS.SSa.IMuSa.FfabMag; both types may have surface sand waves which may be indicative of the presence of venerid bivalves (Warwick & Davies 1977). This hypothesis, however, requires testing. Remote grab sampling is likely to under-estimate venerid bivalves and other deep-burrowing and more dispersed species such as Paphia, Ensis and Spatangus. In southern areas of the UK and the North Sea, in slightly siltier sand and shelly sand, SS.SCS.ICS.MoeVen may give way to the other Spisula biotope SS.SSa.IMuSa.SsubNhom. Together these two biotopes replace the old biotope IGS.FaG.Sell. A variation of the biotope may include the presence of maerl, which may support diverse epifaunal communties and act as a transition between biotopes.
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