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European Nature Information System Level 3 Habitats

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URI http://vocab.nerc.ac.uk/collection/C35/current/
DescriptionMedium-granularity (hierarchical level 3 of 5) terms describing the environment associated with an activity from a biological perspective.
CreatorEuropean Environment Agency
Modified2010-02-19
Version Info1
Identifier C35
Register Manager British Oceanographic Data Centre
Register Owner European Environment Agency
Members
Identifier PrefLabel Definition Date
A4_1 Atlantic and Mediterranean high energy circalittoral rock Occurs on extremely wave-exposed to exposed circalittoral bedrock and boulders subject to tidal streams ranging from strong to very strong. Typically found in tidal straits and narrows. The high energy levels found within this habitat complex are reflected in the fauna recorded. Sponges such as [Pachymatisma johnstonia], [Halichondria panicea], [Esperiopsis fucorum] and [Myxilla incrustans] may all be recorded. Characteristic of this habitat complex is the dense 'carpet ' of the hydroid [Tubularia indivisa]. The barnacle [Balanus crenatus] is recorded in high abundance on the rocky substrata. On rocky outcrops, [Alcyonium digitatum] is often present. 2010-02-18
A3_1 Atlantic and Mediterranean high energy infralittoral rock Rocky habitats in the infralittoral zone subject to exposed to extremely exposed wave action or strong tidal streams. Typically the rock supports a community of kelp [Laminaria hyperborea] with foliose seaweeds and animals, the latter tending to become more prominent in areas of strongest water movement. The depth to which the kelp extends varies according to water clarity, exceptionally (e.g. St Kilda) reaching 45 m. The sublittoral fringe is characterised by dabberlocks [Alaria esculenta]. 2010-02-18
A4_3 Atlantic and Mediterranean low energy circalittoral rock Occurs on wave-sheltered circalittoral bedrock and boulders subject to mainly weak/very weak tidal streams. The biotopes identified within this habitat type are often dominated by encrusting red algae, brachiopods ([Neocrania anomala]) and ascidians ([Ciona intestinalis] and [Ascidia mentula]). 2010-02-18
A3_3 Atlantic and Mediterranean low energy infralittoral rock Infralittoral rock in wave and tide-sheltered conditions, supporting silty communities with [Laminaria hyperborea] and/or [Laminaria saccharina] (A3.31). Associated seaweeds are typically silt-tolerant and include a high proportion of delicate filamentous types. In turbid-water estuarine areas, the kelp and seaweeds (A3.32) may be replaced by animal-dominated communities (A3.36) whilst stable hard substrata in lagoons support distinctive communities (A3.34). 2010-02-18
A4_2 Atlantic and Mediterranean moderate energy circalittoral rock Mainly occurs on exposed to moderately wave-exposed circalittoral bedrock and boulders, subject to moderately strong and weak tidal streams. This habitat type contains a broad range of biological subtypes, from echinoderms and crustose communties (A4.21) to Sabellaria reefs (A4.22) and circalittoral mussel beds (A4.24). 2010-02-18
A3_2 Atlantic and Mediterranean moderate energy infralittoral rock Predominantly moderately wave-exposed bedrock and boulders, subject to moderately strong to weak tidal streams. On the bedrock and stable boulders there is typically a narrow band of kelp [Laminaria digitata] in the sublittoral fringe which lies above a [Laminaria hyperborea] forest and park. Associated with the kelp are communities of seaweeds, predominantly reds and including a greater variety of more delicate filamentous types than found on more exposed coasts (cf. A3.11). 2010-02-18
A4_4 Baltic exposed circalittoral rock Rock habitats in the Baltic infralittoral zone which are exposed to wave action, currents or ice scouring. The exposure status is that impacting on the area concerned at the relevant scale. Thus there may be enclaves of different exposure status caused by localised variation in relief (e.g. steeper rock in more moderately exposed or even sheltered areas). Note that it has been proposed that ?exposed? has an effective fetch of greater than 25 km: this requires verification across the Baltic. 2010-02-18
A3_4 Baltic exposed infralittoral rock Rock habitats in the Baltic infralittoral zone which are exposed to wave action, currents or ice scouring. The exposure status is that impacting on the area concerned at the relevant scale. Thus there may be enclaves of different exposure status caused by localised variation in relief (e.g. steeper rock in more moderately exposed or even sheltered areas). Note that it has been proposed that ?exposed? has an effective fetch of greater than 25 km: this requires verification across the Baltic. 2010-02-18
A4_5 Baltic moderately exposed circalittoral rock Rock habitats in the Baltic infralittoral zone which are moderately exposed to wave action, currents or ice scouring. The exposure status is that impacting on the area concerned at the relevant scale. Thus there may be enclaves of different exposure status caused by localised variation in relief (e.g. steeper rock in sheltered areas). Note that it has been proposed that ?exposed? has an effective fetch of 5 ? 25 km: this requires verification across the Baltic. 2010-02-18
A3_5 Baltic moderately exposed infralittoral rock Rock habitats in the Baltic infralittoral zone which are moderately exposed to wave action, currents or ice scouring. The exposure status is that impacting on the area concerned at the relevant scale. Thus there may be enclaves of different exposure status caused by localised variation in relief (e.g. steeper rock in sheltered areas). Note that it has been proposed that ?exposed? has an effective fetch of 5 ? 25 km: this requires verification across the Baltic. 2010-02-18
A4_6 Baltic sheltered circalittoral rock Rock habitats in the Baltic infralittoral zone which are sheltered from wave action, currents or ice scouring. The exposure status is that impacting on the area concerned at the relevant scale. Thus there may be enclaves of different exposure status caused by localised variation in relief (e.g. sheltered areas within exposed or moderately exposed areas). Note that it has been proposed that ?exposed? has an effective fetch less than 5 km: this requires verification across the Baltic. 2010-02-18
A3_6 Baltic sheltered infralittoral rock Rock habitats in the Baltic infralittoral zone which are sheltered from wave action, currents or ice scouring. The exposure status is that impacting on the area concerned at the relevant scale. Thus there may be enclaves of different exposure status caused by localised variation in relief (e.g. sheltered areas within exposed or moderately exposed areas). Note that it has been proposed that ?exposed? has an effective fetch less than 5 km: this requires verification across the Baltic. 2010-02-18
A8_3 Brine channels During freezing of seawater, salt is rejected from the ice crystals. The remaining brine solution forms a three-dimensional network of tubes and channels with typical diameters of 200 ?m within the ice matrix. Despite the harsh environmental conditions (low light intensities, low temperature, high salinity), a specialised community has developed and adapted to live within the brine channel system. Minute unicellular algae like diatoms are the dominant primary producers. 2010-02-18
A2_5 Coastal saltmarshes and saline reedbeds Angiosperm-dominated stands of vegetation, occurring on the extreme upper shore of sheltered coasts and periodically covered by high tides. The vegetation develops on a variety of sandy and muddy sediment types and may have admixtures of coarser material. The character of the saltmarsh communities is affected by height up the shore, resulting in a zonation pattern related to the degree or frequency of immersion in seawater. 2010-02-18
A7_3 Completely mixed water column with full salinity A water column which is completely and actively mixed, not influenced by freshwater, so that the salinity is the same as that in adjacent seawater. This habitat type is usually found in relatively shallow, coastal situations, without river inflow or ice melt. 2010-02-18
A7_2 Completely mixed water column with reduced salinity A water column which is completely and actively mixed, and influenced by freshwater so that the salinity is reduced relative to the adjacent fully marine seawater. This habitat type is usually found in relatively shallow, coastal situations, and is the result of river inflow or ice melt. Note that some discretion should be used in the interpretation of ?adjacent?, for example in the Baltic Sea, ?adjacent? fully marine seawater is reached only in the Kattegat. 2010-02-18
A6_6 Deep-sea bioherms A bioherm is a mound, dome, or reef-like mass of rock that is composed almost exclusively of the remains of sedentary marine organisms and is embedded in rock of different physical character. This habitat type includes deep-sea coral reefs (A6.61) and sponge beds (A6.62). 2010-02-18
A6_2 Deep-sea mixed substrata Deep-sea benthic habitats with substrates predominantly of mixed particle size or gravel. Includes habitats with mobile substrates of biogenic origin but no longer living, and of allochthonous material such as macrophyte debris. Deep-sea habitats with living biogenic substrates are included in A6.6. 2010-02-18
A6_5 Deep-sea mud Bathyal and abyssal benthic habitats with substrates predominantly of yellowwish or blue-grey mud, relatively consistent, whose population is extremely sparse. This biocoenosis is characterised by constant homothermy and an almost total absence of light. 2010-02-18
A6_4 Deep-sea muddy sand Deep-sea benthic habitats with substrates predominantly of sand. 2010-02-18
A6_1 Deep-sea rock and artificial hard substrata Deep-sea benthic habitats with substrates predominantly of bedrock, immobile boulders or artificial hard substrates. 2010-02-18
A6_3 Deep-sea sand Deep-sea benthic habitats with substrates predominantly of sand. 2010-02-18
A6_8 Deep-sea trenches and canyons, channels, slope failures and slumps on the continental slope Habitats on the deep-sea bed significantly below the deep-sea bed, including deep ocean trenches, often greater than 6000 m depth with an active margin reduction zone (A6.82), and downslope or along-slope channels on the deep-sea bed (A6.81). 2010-02-18
A4_7 Features of circalittoral rock Circalittoral rock features include circalittoral fouling communities (A4.72) and circalittoral caves and overhangs (A4.71). These features are present throughout the circalittoral zone in a variety of wave exposures and tidal streams. Two fouling subtypes have also been identified: A4.722 has been recorded from disused fishing nets and other artificial substrata, and is characterised by aggregations of [Ascidiella aspersa] whilst A4.721 has been recorded from steel wrecks, and is characterised by dense aggregations of [Alcyonium digitatum] and [Metridium senile]. Habitats in hard substrata in the circalittoral zone characterised by the presence of seeping or bubbling gases, oils or water are also included (A4.73). 2010-02-18
A3_7 Features of infralittoral rock Includes surge gulleys (A3.71), which are found throughout the infralittoral rock zone, and usually consist of vertical bedrock walls, occasionally with overhanging faces, and support communities, which reflect the degree of wave surge they are subject to and any scour from mobile substrata on the cave/gully floors. The larger cave and gully systems, such as found in Shetland, Orkney, the Western Isles and St Kilda, typically show a marked zonation from the entrance to the rear of the gully/cave as wave surge increases and light reduces. Also includes habitats in hard substrata in the infralittoral zone characterised by the presence of seeping or bubbling gases, oils or water (A3.73) and recently colonised artificial hard substrata in the infralittoral zone (A3.72). 2010-02-18
A1_4 Features of littoral rock Littoral rock features include rockpools (A1.41, A1.42), ephemeral algae (A1.45) and caves (A1.44) in the intertidal zone (the area of the shore between high and low tides). These features are present throughout the littoral rock zone from the upper limit at the top of of the lichen zone and the lower limit by the top of the laminarian kelp zone. These features can be found on most rocky shores regardless of wave exposure. Lichens can be found in the supralittoral zone on shores with suitable substratum. The lichen band is wider and more distinct on more exposed shores. Rockpools occur where the topography of the shore allows seawater to be retained within depressions in the bedrock producing 'pools ' on the retreat of the tide. As these rockpool communities are permanently submerged they are not directly affected by height on the shore and normal rocky shore zonation patterns do not apply allowing species from the sublittoral to survive. Ephemeral seaweeds occur on disturbed littoral rock in the lower to upper shore. The shaded nature of caves and overhangs diminishes the amount of desiccation suffered by biota during periods of low tides which allows certain species to proliferate. In addition, the amount of scour, wave surge, sea spray and penetrating light determines the unique community assemblages found in upper, mid and lower shore caves, and on overhangs on the lower shore. Non-tidal areas irregularly exposed by wind action (hydrolittoral) with hard substrata are also included here. Note that lichens and algae crusts in the supralittoral zone are coastal habitats (B3.11). 2010-02-18
A2_8 Features of littoral sediment Features of littoral sediment include littoral habitats characterised by the presence of gases or liquids bubbling or seeping through sediments (A2.81); areas which are characterised by pioneer or ephemeral red and green algae because of variations in salinity and/or siltation (A2.82); and sedimentary shores of non-tidal, reduced salinity waters which are below the mean water level and normally water-covered, but which are regularly or occasionally exposed by the action of wind (hydrolittoral zone in the Baltic) (A2.83-A2.87). 2010-02-18
A5_7 Features of sublittoral sediments Features of sublittoral sediments include sublittoral habitats characterised by the presence of gases or liquids bubbling or seeping through sediments (A5.71) and sublittoral sediments which are organically-enriched or permanently or periodically anoxic (A5.72). 2010-02-18
A8_2 Freshwater ice Floating and drifting blocks of ice detached from coastal glaciers (H4.2). These are separated by size at level 4. 2010-02-18
A7_A Fronts in full salinity water column A water column which is unmixed or only partially mixed because the depth of the water body is greater than the depth of mixing. Salinity is the same as that in adjacent seawater. Horizontal gradients give rise to fronts, which are separated at level 4 by the degree of persistence of the stratification ? ephemeral such as eddies, gyres and upwellings; seasonal upwellings; or persistent water mass interfaces. 2010-02-18
A7_7 Fronts in reduced salinity water column A water column which is unmixed or only partially mixed because the depth of the water body is greater than the depth of mixing, and with short residence time, defined as changing diurnally. Salinity is reduced relative to the adjacent fully marine seawater. This habitat type is usually found in deeper coastal water situations and is the result of river inflow or ice melt. Note that some discretion should be used in the interpretation of ?adjacent?, for example in the Baltic Sea, ?adjacent? fully marine seawater is reached only in the Kattegat. Horizontal gradients give rise to fronts, which are separated at level 4 by the degree of persistence of the stratification. 2010-02-18
A1_1 High energy littoral rock Extremely exposed to moderately exposed or tide-swept bedrock and boulder shores. Extremely exposed shores dominated by mussels and barnacles, occasionally with robust fucoids or turfs of red seaweed. Tide-swept shores support communities of fucoids, sponges and ascidians on the mid to lower shore. Three biological subtypes have been described: Communities on very exposed to moderately exposed upper and mid eulittoral bedrock and boulders dominated by the mussel [Mytilus edulis], barnacles [Chthamalus] spp. and/or [Semibalanus balanoides] and the limpets [Patella] spp. (A1.11); red and brown seaweeds able to tolerate the extreme conditions of exposed rocky shores, primarily the physical stresses caused by wave action (A1.12), and tide-swept shores in more sheltered areas (such as narrow channels in sea loch) with canopy forming fucoids and a rich filter-feeding community (A1.15). 2010-02-18
A2_7 Littoral biogenic reefs The Littoral Biogenic Reefs habitat contains two biological subtypes, littoral [Sabellaria] reefs (A2.71) and mixed sediment shores with mussels (A2.72), encompassing the littoral biotope dominated by the honeycomb worm [Sabellaria alveolata], and littoral [Mytilus edulis]- dominated communities. [S. alveolata] can form honeycomb reefs on mid to lower shore on exposed coasts, where there is a plentiful supply of sediment. The underlying substratum may consist primarily of rock or stable cobbles and boulders, or of cobbles and boulders on sand. Mixed sediment shores characterised by beds of adult mussels [Mytilus edulis] occur principally on mid and lower eulittoral mixed substrata (mainly cobbles and pebbles on muddy sediments) in a wide range of exposure conditions. In high densities the mussels bind the substratum and provide a habitat for many infaunal and epifaunal species. Temporal variation: [S. alveolata] reefs may be susceptible to storm damage in the winter, although they can regenerate remarkably quickly in a season as long as some adults are left as they facilitate the larval settlement. [S. alveolata] is tolerant to burial under sand for several weeks. Changes in desiccation over a period of time can cause part of the population to die. One of the mussel-dominated subtypes, A2.7212, could change to A2.7213 over time as pseudofaeces build up forming a layer of mud. This cannot happen where wave action or tidal streams wash away pseudofaeces and prevent a build up. In areas where mussel spat ("mussel crumble") settles on the surface shell layer of cockle beds, the mussel cover may be ephemeral. 2010-02-18
A2_1 Littoral coarse sediment Littoral coarse sediments include shores of mobile pebbles, cobbles and gravel, sometimes with varying amounts of coarse sand. The sediment is highly mobile and subject to high degrees of drying between tides. As a result, few species are able to survive in this environment. Beaches of mobile cobbles and pebbles tend to be devoid of macroinfauna, while gravelly shores may support limited numbers of crustaceans, such as [Pectenogammarus planicrurus]. Situation: Littoral coarse sediments are found along relatively exposed open shores, where wave action prevents finer sediments from settling. Coarse sediments may also be present on the upper parts of shores where there are more stable, sandy biotopes on the lower and mid shore. Temporal variation: The sediment particle size structure may vary seasonally, with relatively finer sediments able to settle during calmer conditions in summer. Where the sediment grain size is very large (at the interface between sediment and boulder shores), cobbles may be mobile during exposed winter conditions, but stable enough during summer months to support limited juvenile rocky shore epifauna (e.g. juvenile barnacles). 2010-02-18
A2_4 Littoral mixed sediments Shores of mixed sediments ranging from muds with gravel and sand components to mixed sediments with pebbles, gravels, sands and mud in more even proportions. By definition, mixed sediments are poorly sorted. Stable large cobbles or boulders may be present which support epibiota such as fucoids and green seaweeds more commonly found on rocky and boulder shores. Mixed sediments which are predominantly muddy tend to support infaunal communities which are similar to those of mud and sandy mud shores. Situation: It is probable that there are broad transition areas between areas of mudflat or sandy mudflat, and mixed sediment biotopes where the sediment consists principally of mud but has significant proportions of gravel and sand mixed in. Gravelly mud may occur in patches on mudflats. Similarly, there is unlikely to be an easily defined boundary between areas of mixed sediment with stable cobbles and boulders, and boulder fields which fall into the rocky shore category. 2010-02-18
A2_3 Littoral mud Shores of fine particulate 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. Littoral mud can support communities characterised by polychaetes, bivalves and oligochaetes. Most muddy shores are subject to some freshwater influence, as most of them occur along the shores of estuaries. Mudflats on sheltered lower estuarine shores can support a rich infauna, whereas muddy shores at the extreme upper end of estuaries and which are subject to very low salinity often support very little infauna. Situation: Muddy shores are principally found along the shores of estuaries where there is enough shelter from wave action to allow fine sediment to settle. Muddy shores may also be present in sheltered inlets, straits and embayments which are not part of major estuarine systems. 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. 2010-02-18
A2_2 Littoral sand and muddy sand Shores comprising clean sands (coarse, medium or fine-grained) and muddy sands with up to 25% silt and clay fraction. Shells and stones may occasionally be present on the surface. The sand may be duned or rippled as a result of wave action or tidal currents. Littoral sands exhibit varying degrees of drying at low tide depending on the steepness of the shore, the sediment grade and the height on the shore. The more mobile sand shores are relatively impoverished (A2.22), with more species-rich communities of amphipods, polychaetes and, on the lower shore, bivalves developing with increasing stability in finer sand habitats (A2.23). Muddy sands (A2.24), the most stable within this habitat complex, contain the highest proportion of bivalves. Situation: A strandline of talitrid amphipods (A2.211) typically develops at the top of the shore where decaying seaweed accumulates. Fully marine sandy shores occur along stretches of open coast, whilst muddy sands are often present in more sheltered lower estuarine conditions and may be subject to some freshwater influence. Temporal variation: Littoral sandy shore environments can change markedly over seasonal cycles, with sediment being eroded during winter storms and accreted during calmer summer months. The particle size structure of the sediment may change from finer to coarser during winter months, as finer sediment gets resuspended in seasonal exposed conditions. This may affect the sediment infauna, with some species only present in summer when sediments are more stable. More sheltered muddy sand shores are likely to be more stable throughout the year, but may have a seasonal cover of green seaweeds during the summer period, particularly in nutrient enriched areas or where there is freshwater input. 2010-02-18
A2_6 Littoral sediments dominated by aquatic angiosperms Dominants are [Eleocharis acicularis], [Eleocharis parvula], [Zostera] spp. 2010-02-18
A1_3 Low energy littoral rock Sheltered to extremely sheltered rocky shores with very weak to weak tidal streams are typically characterised by a dense cover of fucoid seaweeds which form distinct zones (the wrack [Pelvetia canaliculata] on the upper shore through to the wrack [Fucus serratus] on the lower shore). Where salinity is reduced (such as at the head of a sea loch or where streams run across the shore) [Fucus ceranoides] may occur. Fucoids also occur on less stable, mixed substrata (cobbles and pebbles on sediment) although in lower abundance and with fewer associated epifaunal species; beds of mussels [Mytilus edulis] are also common. In summer months, dense blankets of ephemeral green and red seaweeds can dominate these mixed shores. Two biological subtypes have been described: Dense blankets of fucoid seaweeds dominating sheltered, fully marine littoral rocky shores (A1.31) and fucoids dominating variable salinity rocky shores (A1.32). 2010-02-18
A1_2 Moderate energy littoral rock Moderately exposed shores (bedrock, boulders and cobbles) characterised by mosaics of barnacles and fucoids on the mid and upper shore; with fucoids and red seaweed mosaics on the lower shore. Where freshwater or sand-scour affects the shore ephemeral red or green seaweeds can dominate. Other shores support communities of mussels and fucoids in the mid to lower shore. Two biological subtypes have been described: barnacles and fucoids (A1.21) and mussels and fucoids (A1.22). 2010-02-18
A7_1 Neuston The interface between air and sea water, inhabited by communities of minute or microscopic organisms. 2010-02-18
A7_4 Partially mixed water column with reduced salinity and medium or long residence time A water column which is unmixed or only partially mixed because the depth of the water body is greater than the depth of mixing. Salinity is reduced relative to the adjacent fully marine seawater. This habitat type is usually found in deeper coastal water situations and is the result of river inflow or ice melt. Note that some discretion should be used in the interpretation of ?adjacent?, for example in the Baltic Sea, ?adjacent? fully marine seawater is reached only in the Kattegat. Medium residence time is defined as changing over time preiods greater than daily and up to about 14 days (based on the time required for the phytoplankton population to double) and long residence time lasting longer than 14 days. 2010-02-18
A6_7 Raised features of the deep-sea bed Habitats on the deep-sea bed with significant elevation (typically >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). 2010-02-18
A8_1 Sea ice Ice formations floating on sea water, usually constituting an incomplete cover, variable in form and structure, unstable and dynamic under the influence of surface air and water currents. 2010-02-18
A5_6 Sublittoral biogenic reefs This habitat type includes polychaete reefs, bivalve reefs (e.g. mussel beds) and cold water coral reefs. These communities develop in a range of habitats from exposed open coasts to estuaries, marine inlets and deeper offshore habitats and may be found in a variety of sediment types and salinity regimes. 2010-02-18
A5_1 Sublittoral coarse sediment Coarse sediments including coarse sand, gravel, pebbles, shingle and cobbles which are often unstable due to tidal currents and/or wave action. These habitats are generally found on the open coast or in tide-swept channels of marine inlets. They typically have a low silt content and a lack of a significant seaweed component. They are characterised by a robust fauna including venerid bivalves. 2010-02-18
A5_5 Sublittoral macrophyte-dominated sediment This habitat type includes maerl beds, seaweed dominated mixed sediments (including kelps such as [Laminaria saccharina] and filamentous/foliose red and green algae), seagrass beds, and lagoonal angiosperm communities. These communities develop in a range of habitats from exposed open coasts to lagoons and are found in a variety of sediment types and salinity regimes. 2010-02-18
A5_4 Sublittoral mixed sediments Sublittoral mixed (heterogeneous) sediments found from the extreme low water mark to deep offshore circalittoral habitats. These habitats incorporate a range of sediments including heterogeneous muddy gravelly sands and also mosaics of cobbles and pebbles embedded in or lying upon sand, gravel or mud. There is a degree of confusion with regard nomenclature within this complex as many habitats could be defined as containing mixed sediments, in part depending on the scale of the survey and the sampling method employed. The BGS trigon can be used to define truly mixed or heterogeneous sites with surficial sediments which are a mixture of mud, gravel and sand. However, another 'form ' of mixed sediment includes mosaic habitats such as superficial waves or ribbons of sand on a gravel bed or areas of lag deposits with cobbles/pebbles embedded in sand or mud and these are less well defined and may overlap into other habitat or biological subtypes. These habitats may support a wide range of infauna and epibiota including polychaetes, bivalves, echinoderms, anemones, hydroids and Bryozoa. Mixed sediments with biogenic reefs or macrophyte dominated communities are classified separately in A5.6 and A5.5 respectively. 2010-02-18
A5_3 Sublittoral mud Sublittoral mud and cohesive sandy mud extending from the extreme lower shore to offshore, circalittoral habitats. This biotope is predominantly found in sheltered harbours, sealochs, bays, marine inlets and estuaries and stable deeper/offshore areas where the reduced influence of wave action and/or tidal streams allow fine sediments to settle. Such habitats are often by dominated by polychaetes and echinoderms, in particular brittlestars such as [Amphiura] spp. Seapens such as [Virgularia mirabilis] and burrowing megafauna including [Nephrops norvegicus] are common in deeper muds. Estuarine muds tend to be characterised by infaunal polychaetes and oligochaetes. 2010-02-18
A5_2 Sublittoral sand Clean medium to fine sands or non-cohesive slightly muddy sands on open coasts, offshore or in estuaries and marine inlets. Such habitats are often subject to a degree of wave action or tidal currents which restrict the silt and clay content to less than 15%. This habitat is characterised by a range of taxa including polychaetes, bivalve molluscs and amphipod crustacea. 2010-02-18
A8_4 Under-ice habitat The boundary layer between sea ice and the water column with special abiotic (e.g. temperature, salinity) and biotic (e.g. food resources) factors, which also vary with season and region. This habitat is colonized by autochthonous under-ice amphipods ([Apherusa glacialis], [Onisimus] spp., [Gammarus wilkitzkii]), which live directly at the ice underside and complete their entire life-cycle here, and allochthonous sub-ice fauna, organisms originating either from the ice interior or the pelagic realm, which are found in this boundary layer temporarily, e.g. for feeding or during certain life stages. There is some evidence that the first metres below the ice are strongly stratified, particularly during the melt period in summer. Source: http://www.awi-bremerhaven.de/Climate/WorkingGroups/ofis/ARK-19-1/sea-ice-biology.htm. 2010-02-18
A7_8 Unstratified water column with full salinity A water column which is unmixed or only partially mixed because the depth of the water body is greater than the depth of mixing. Salinity is the same as that in adjacent seawater. Unstratified water columns have very weak or no horizontal or vertical gradients. 2010-02-18
A7_5 Unstratified water column with reduced salinity A water column which is unmixed or only partially mixed because the depth of the water body is greater than the depth of mixing, and with short residence time, defined as changing diurnally. Salinity is reduced relative to the adjacent fully marine seawater. This habitat type is usually found in deeper coastal water situations and is the result of river inflow or ice melt. Note that some discretion should be used in the interpretation of ?adjacent?, for example in the Baltic Sea, ?adjacent? fully marine seawater is reached only in the Kattegat. Unstratified water columns have very weak or no horizontal or vertical gradients. 2010-02-18
A6_9 Vents, seeps, hypoxic and anoxic habitats of the deep sea Deep-sea habitats characterised by chemical conditions. Includes interface habitats on the deep-sea bed where reducing conditions exist (A6.91), not generally associated with drastically elevated temperatures, including the carcasses of large cetaceans (A6.913). These habitats are often indicated by the presence of seeping or bubbling gases or liquids, hypoxic and/or anoxic conditions in the water column above. Also includes vents in the deep-sea bed (A6.94). 2010-02-18
A7_9 Vertically stratified water column with full salinity A water column which is unmixed or only partially mixed because the depth of the water body is greater than the depth of mixing. Salinity is the same as that in adjacent seawater. This habitat type shows pronounced vertical stratification (e.g. caused by atmospheric temperature). The subtypes are separated at level 4 by the cause and degree of persistence of the gradient ? e.g. seasonal temperature gradients or persistent salinity gradients. 2010-02-18
A7_6 Vertically stratified water column with reduced salinity A water column which is unmixed or only partially mixed because the depth of the water body is greater than the depth of mixing, and with short residence time, defined as changing diurnally. Salinity is reduced relative to the adjacent fully marine seawater. This habitat type is usually found in deeper coastal water situations and is the result of river inflow or ice melt. Note that some discretion should be used in the interpretation of ?adjacent?, for example in the Baltic Sea, ?adjacent? fully marine seawater is reached only in the Kattegat. Unstratified water columns have very weak or no horizontal or vertical gradients. 2010-02-18