MHI urn:sandre:dictionnaire:sa_mhi::2 Description des milieux humides 2014 Ce document décrit les concepts qui définissent un milieu humide. OIEau, ONEMA, MNHN, AESN , AELB, Forum des Marais Atlantiques,DEB 2 Milieux Humides France fra 2013-11-27 2014-04-01 2014-04-01 Validé -----------------Entités----------------- ZONE HUMIDE D'IMPORTANCE INTERNATIONALE SITE RAMSAR MILIEU HUMIDE ALIAS DU NOM DU MILIEU HUMIDE ZONE HUMIDE LOI SUR L'EAU ZHIEP ZSGE MILIEU HUMIDE AUTRE GENEALOGIE DU MILIEU HUMIDE -----------------Attributs----------------- ). Elle est rattachée au Milieu Humide de niveau d'approche 'Précis'. Les valeurs possibles sont définies dans la nomenclature n°364]]> 140 m with polychaetes [Lumbrineris fragilis], [Levinsenia gracilis] and amphipods [Eriopisa elongata]]]> 20% mud) may support communities characterised by infaunal polychaetes and the bivalve [Myrtea spinifera]. Polychaetes typically include [Chaetozone setosa], [Paramphinome jeffreysii], [Levinsenia gracilis], [Aricidea catherinae] and [Prionospio malmgreni]. The bivalves [Thyasira] spp. and [Abra nitida] may also be found as may seapens, such as [Pennatula phosphorea]. Some examples of the biotope AfilNten contain [Myrtea spinifera] (Mackie 1990) in lower numbers but these habitats are generally sandier than those in MyrPo._x000D_ Situation: This biotope has been recorded in the northern North Sea but may also exist in the Irish Sea.]]> Frequent) refer to MIR.LsacChoR and MIR.HalXK respectively. Although the faunal component of this biotope is usually relatively sparse it can include a wide variety of species. Turfs of hydroids ([Nemertesia] spp., [Aglaophenia tubulifera]) and bryozoans ([Crisia] spp. and [Bugula] spp.) are the major components but sponges and anemones may also occur. Brittlestars, sea-urchins, hydroids and solitary ascidians are more prominent in the Scottish examples of this biotope, which tend to occur in deeper water, due in part to clearer waters._x000D_ Situation: Although not common, this biotope is widely distributed from Sussex to the shallow areas of the Sarns in Cardigan Bay, the west coast of Scotland and the north-east coast of Ireland. Despite the wide distribution, the red seaweed composition remains remarkably constant. In areas such as the Sarns, in Wales, where mixed substrata continue into the shallows, dense swathes of HIR.LsacChoR can be found. More stable but highly scoured areas adjacent to LsacR.CbPb can support the [Halidrys] biotope HIR.XKHal. Where bedrock or large boulders occur above the mixed substrata of LsacR.CbPb it may support a kelp forest or park (HIR.LhypR or MIR.Lhyp). At many sites the mixed substrata supporting the dense seaweed turf gives way to sediment of varying composition._x000D_ Temporal variation: This biotope will take on a much more depauperate appearance during the winter months, once the ephemeral seaweeds have died back in late summer/autumn. Storms can mobilise the loose pebbles and cobbles, removing all but the most resilient of seaweeds and animals. By summer, under more stable conditions, new growth will flourish and dense stands of seaweeds dominate the seabed.]]> 2000 m on the continental slope, and in shallower waters in Norwegian fjords and Swedish west coast. In Norwegian waters, [L. pertusa] reefs occur on the shelf and shelf break off the western and northern parts on local elevations of the sea floor and on the edges of escarpments. The biological diversity of the reef community is approximately three times as high as the surrounding soft sediment (ICES, 2003), suggesting that these cold-water coral reefs may be biodiversity hotspots. Characteristic species include other hard corals, such as [Madrepora oculata] and [Solenosmilia variabilis], the redfish [Sebastes viviparous] and the squat lobster [Munida sarsi]. [L. pertusa] reefs occur on hard substrata; this may be [Lophelia] rubble from an old colony or on glacial deposits. For this reason, [L. pertusa] reefs can be associated with iceberg plough-mark zones.]]> 2000m on the continental slope, and in shallower waters in Norwegian fjords and Swedish west coast. In Norwegian waters, L. pertusa reefs occur on the shelf and shelf break off the western and northern parts on local elevations of the sea floor and on the edges of escarpments. The biological diversity of the reef community is approximately three times as high as the surrounding soft sediment (ICES, 2003), suggesting that these cold-water coral reefs may be biodiversity hotspots. Characteristic species include other hard corals, such as Madrepora oculata and Solenosmilia variabilis, the redfish Sebastes viviparous and the squat lobster Munida sarsi. L. pertusa reefs occur on hard substrata; this may be Lophelia rubble from an old colony or on glacial deposits. For this reason, L. pertusa reefs can be associated with iceberg plough-mark zones.]]> 200m) in relation to their surroundings. Includes permanently submerged flanks of oceanic islands (A6.71), seamounts, knolls and banks (A6.72), oceanic ridges (A6.73), abyssal hills (A6.74) and carbonate mounds (A6.75).]]> 7). Les eaux modérément eutrophes peuvent héberger des tapis denses de macrophytes, mais ceux-ci disparaissent lorsque la teneur en nutriments s’élève du fait de la pollution.]]> 7).]]> 7,5).]]>