Marine deep waters

• Innhold
• Description of marine deep waters
• Assessment areas
• Assessed Ecosystem Types
• Ecosystem Types on the Red List
• Impact factors
• Existing knowledge
• Expert Committee
• References

Marine deep waters (aphotic seabeds) comprises marine ecosystem types where there is insufficient light for the survival of algae. The upper depth limit varies according to local conditions that influence light penetration through the water. The depth to which algal vegetation extends varies between sheltered and exposed areas. In this assessment we have used 40 m as a realistic upper depth limit, an approximation of the boundary between the upper and lower sublittoral zones.

Description of marine deep waters

The marine deep waters extend over sizeable geographic distances with shallower shelf areas, continental slopes and abyssal plains. Skagerrak and the North Sea in the south, the Norwegian Sea in the west, and the Barents Sea in the north, are influenced by different ocean currents, and with a varied bottom topography this forms the basis of a series of ecosystem types with considerable variation, even over short distances.

The extensive deep sea areas in the Norwegian Sea, below the continental shelf, and deeper than approximately 600 metres deep, have extremely cold waters that provide essential habitat conditions for the fauna, and different from conditions on the continental shelf and along the coast. Within the entire area, as well as the areas around Svalbard and Jan Mayen, there are a number of special ecosystem types, examples of which include hydrothermal vents, mud volcanoes and cold seeps.

The major ecosystem types in the marine deep waters are divided into minor types based on environmental variables related to depth (water masses and depth zones), environmental stability (including temperature variation) and substrate stability (fine sediment types and rock substrates). Large sessile species such as corals and sponges are characteristic of ecosystem types that are commonly referred to as "coral gardens", "coral reefs" and "sponge grounds". The large sessile organisms that make up these ecosystem types are exposed to physical disturbances such as demersal fishing, anchoring, and dumping of aggregate. Gorgonians can occur as the dominant megafauna on both marine rock and sediment in areas with both Atlantic waters (originating from the Gulf Stream) and Arctic intermediate waters (with origins in the Arctic). In terms of area, coral gardens dominate marine rock substrate areas, where the species that most often forms such communities is the larger Gorgonian Paragorgia arborea. This is an extremely fragile species that is vulnerable to contact with commercial fishing gear. On soft bottom substrates the bamboo coral Isidella lofotensis can dominate in the fjords, but in the deep sea the sea whip "pigtail" corals Radicipes sp. can form an equivalent ecosystem type. Sea pens are another order of Anthozoa (a class which includes sea anemones and corals) which is exposed to physical disturbance, first and foremost from bottom trawling. Nevertheless, in general there is little overlap between the areas which are trawled and areas with a known distribution of sea pens, apart from in the Skagerrak where there is a risk of overlap with prawn fishing. Sponges are also structure-forming organisms and are particularly dominant on parts of the continental shelf and seamounts along the mid-ocean ridge in the Norwegian Sea. In coastal and shelf areas in particular, there is a considerable overlap with areas where bottom trawling takes place.

Assessment areas

The areas that are assessed encompass the ocean areas around the Norwegian mainland, which in addition to the territorial waters of Norway (i.e. all marine areas within the territorial border) comprise the Norwegian economic zone (200 nautical miles, approximately 965 000 km²), the fishery zone including territorial waters around Svalbard (200 nautical miles, approximately 861 000 km²), and the fishing zone, including territorial waters, around Jan Mayen (200 nautical miles, approximately 293 000 km²). Norwegian marine areas therefore comprise approximately 2.1 million km².

Assessed Ecosystem Types

In the NiN-system marine deep waters comprises five major types for marine seabeds, all of which are assessed: Aphotic marine rock M2, Aphotic marine sediment M5, Coral reef seabed M6, Marine cold seep M11 and Hydrothermal vent M12. There are, furthermore, two major types that also occur in shallow waters and are probably more common in shallow coastal areas: Marine cave and overhang M10 and Anoxic marine sediment M13. For practical reasons these are discussed in the chapter on marine shallow waters.

In addition there are defined assessment entities for minor ecosystem types or combinations of minor types under aphotic marine rock and aphotic marine sediment. These assessment entities are defined on the basis of dominance of particular species or due to threats that do not affect the major type in its entirety.

The current assessment also includes marine waterbody systems even though the development of these in NiN is still relatively basic. Marine waterbody systems are divided into three major types: Oceanic waterbody H1, Circulating fjord, estuary, lagoon and rockpool waterbody H2 and Anoxic marine waterbody H3. All the major types occur within both the euphotic and aphotic zones but most of Oceanic waterbody and Anoxic marine waterbody are situated in deeper areas, and these are discussed here. Circulating fjord, estuary, lagoon and rockpool waterbody mainly comprises surface waters and brackish water layers in fjords and estuarine inlets, and is discussed in the chapter on marine shallow waters.

Aphotic marine rock

Aphotic marine rock M2 comprises solid substrates with a grain size larger than a cobble, from boulder size and upwards, and which has a permanent community of perennial sessile species. Aphotic marine rock can occur with or without a thin cover of fine-grained sediments, independent of the gradient of the seabed and exposure to currents. These factors determine the range of species that can occur.

Under Aphotic marine rock an assessment entity is defined for Hard-bottom coral garden that is composed of the minor types (M2-6, M2-7) of moderately sheltered aphotic rock in the sublittoral zone and Atlantic waters dominated by Gorgonians.  These minor types are dominated by Gorgonian corals such as the bubblegum coral Paragorgia arborea, red tree coral Primnoa resedaeformis, and flattened sea fan coral Paramuricea placomus, and they are therefore combined into a separate assessment entity which has similarities in terms of environment and associated fauna. This assessment entity is singled out (selection criterion Type 1.3) on the grounds that the physical impact of fisheries in particular, has a greater negative effect on this assessment entity than on the major type. The assessment entities are defined on the basis of the relative composition of megafauna under the descriptive system in NiN.

Aphotic marine sediment

Aphotic marine sediment M5 is, in terms of area, the largest major type within marine and terrestrial substrates in areas under Norwegian environmental management. Four assessment entities for minor types or combinations of minor types are defined under aphotic marine sediment. Common for these entities is that they are exposed to bottom trawling, partly in areas where there is intensive commercial fishing. They represent ecosystem types that are distinguished by having a particular substrate, being represented by fragile perennial coral species, occuring at only a few localities within a small area, or they are based on variations in the natural landscape. This applies to Sponge spicule bottom in the southern Barents Sea, Soft-bottom bamboo coral garden, Radicipes coral meadows in the areas around Bjørnøya, and Aphotic mud in Skagerrak.

Coral reef seabed

Coral reef seabed is an assessment entity at the major type level and includes both the coastal (M6-1) and the oceanic (M6-2) coral reefs that are defined as separate minor types in NiN 2.0. The impact factors differ for the two types of coral reefs but there is insufficient data to carry out separate assessments. In general, the mapping of coastal coral reefs is of a lower standard than the mapping of reefs on the continental shelf. There is also considerable uncertainty regardinging the extent to which coral reefs will be impacted by climate change and ocean acidification (see separate section). Nineteen coral reef protected areas have been designated in Norway, in the counties of Østfold, Rogaland, Hordaland and all counties north of the county of Sogn and Fjordane. Based on an estimate of the total number of reefs, the proportion of coral reefs that are protected is less than 20 %.

Marine cold seep

Marine cold seep M11 is divided into six minor types. Five of these are defined on the basis of depth zones and the extent to which the seep is stable or unstable (only periodically active). The sixth type is mud volcano (Bathypelagic and abyssal mud vulcano M11-7) which is relatively well-researched (see for example, Perez-Garcia et al. 2009).

Hydrothermal vent

Hydrothermal vent M12 is divided into seven minor types based on whether they are subject to the weak or strong influence of geothermal heat, and according to the depth zone in which they occur. We have not found a basis for carrying out individual assessments of these ecosystem types. There are eight known localities of hydrothermal vents based on the information provided in maps and text by Pedersen et al. (2010) and Olsen et al. (2016), as well as unpublished material that describes the known Norwegian occurrences of hydrothermal vents.

Oceanic waterbody

Oceanic waterbody H1 comprises marine water masses that are in direct contact with the world's oceans without being physically separated from them by a distinct sill as is the case with fjords. In NiN, Oceanic waterbody is divided into four pelagic depth zones (epipelagic, mesopelagic, bathypelagic and abyssopelagic). Furthermore, epipelagic coastal waters are defined on the basis of differences between coastal waters and surface waters in the open ocean. The boundary between bathypelagic and abyssopelagic is not reflected in the dispersion of water masses at corresponding depths (Arctic Intermediate Water and the waters of the Norwegian Sea) and is not used in this assessment. There is no basis for red-listing oceanic waterbodies.

Anoxic marine waterbody

Anoxic marine waterbody H3 describes isolated waterbodies that are in contained in deep basins beyond shallow sills in estuarine inlets and fjords. These waterbodies are anoxic and are characterised by their unique chemical composition and extreme paucity of species. This major type is more accurately defined by the condition that significant water exchange (more than 20 % of the volume) occurs infrequently and not more than every 10 years. Non-circulating waterbodies are poorly mapped but occur mainly in Agder (southern Norway) and Vestlandet (western Norway).

Ecosystem Types on the Red List

A total of twelve ecosystem types have been assessed, five of which were separate assessment entities under the major types Aphotic marine rock and Aphotic marine sediment. All the major types, with the exception of Coral reef seabed M6 have been assessed as being of Least Concern LC. For these types, reductions in area or quality to an extent that would result in red-listing have not been identified.

Coral reef seabed M6 is assessed as Near Threatened NT. This is determined on the basis of a reduction in area and quality (criteria A and C) due to the physical damage inflicted by bottom trawling.

The minor types and minor type combinations Soft-bottom bamboo coral garden and Radicipes coral meadows are both assessed as Endangered EN. For both these types it is an ongoing reduction in quality due to the damage and depletion of coral colonies, as well as a demonstrated negative impact factor (bottom trawling) that is the basis for their placement in this category. Hard-bottom coral garden, Sponge spicule bottom in the southern Barents Sea and Aphotic mud in Skagerrak are assessed as Near Threatened NT. For Aphotic mud bottom trawling is also implicated in the assessment. In this case it is based on environmental degradation due to the loss of organisms and functions in the benthic ecosystem. In general, it is the restricted distribution (area) that determines the assessment of Hard-bottom coral garden. Assessment of changes in the ecological condition of this ecosystem type is based on assessments of stands of the bubblegum coral Paragorgia arborea. This is an extremely fragile species that is sensitive to contact with fishing gear, and video footage shows that commercial fishing leads to concrete damage.

Impact factors

In general, the existing knowledge regarding the effects of impact factors on ecosystem types in marine deep waters is poor. This applies in particular to climate-related changes (temperature increases and ocean acidification), as well as to the effects of increased levels of suspended particulate matter. The oil industry, aquaculture industry, and commercial bottom trawling can all cause local increases in particulate matter values.

Habitat impact

The most important impact factor for all the assessed ecosystem types is habitat impact, which in practice means damage from bottom trawling. Studies have determined that the proportion of coral reefs with physical damage is large. It is estimated that between 30 and 50 % of all reefs off the Norwegian coast are damaged to some degree by bottom trawling. More recent studies have shown that the established marine protected areas for coral reefs are respected, but that new damage occurs at previously unknown reefs. As there is still considerable trawler activity in areas with coral reef, there is a danger that damage will accumulate over time, and more reefs can completely disappear, such as has been observed in many areas off the coast of mid-Norway. It is first and foremost bottom trawling on the continental shelf that is responsible for the greatest impact on the ecosystem types Coral reef seabed, Soft-bottom bamboo coral garden, and Radicipes coral meadows in intermediate waters. The area where Radicipes coral meadows occurs is used as a trawling lane for Greenland halibut Reinhardtius hippoglossoides. This activity is visible in the form of trawl door tracks on the seabed and the presence of coral skeletons.

Bottom trawling can impact corals and sponges in several ways: by detaching them from the substrate, breaking the skeleton/fragmenting the colony, causing tissue damage and necrosis, or clogging the filter apparatus. Sediment disturbance also affects the surrounding biodiversity. It is thought that species that live on corals are affected by the health of the host coral, and when the coral disappears so does the associated fauna. A decline in the density of coral colonies and sponges may reduce the density of larger mobile fauna such as crustaceans and fish.

For coral reef seabeds in the open ocean the greatest documented threat comes from bottom trawling, an activity which is present to a much lesser degree in coastal areas. In coastal areas the distribution of coral reefs and sponge grounds overlaps with areas subject to possible affects from aquaculture, and discharges and runoff from land (agriculture, rivers and sewage). These areas are possibly also subject to the dispersion of particulate matter from the dumping of excavated soil and rock (tunnel-building etc.).

In Hard-bottom coral gardens commercial fishing with longlines and nets is an impact factor. Bottom trawling can also be a factor that is responsible for negative habitat impacts in cold seeps. The removal and destruction of the calcium carbonate substrate can occur in connection with bottom trawling. Habitat impacts can also occur as a result of various activities connected to the extraction of oil and gas.

Particulate matter discharge

The discharge of particulate matter (feed waste and excrement) from fish farms is a factor that can negatively affect ecosystem types dominated by filter feeders (for example coral reef seabeds, coral gardens and sponges) and organism communities on sediment substrates. The scope of the impact of this factor is unknown, as well as the scope and type of impact that an increase in nutrient salts from land-based discharges will have on such organisms.

Climate change

With climate change Coral reef seabed and coral gardens in particular could be negatively affected. Changes in temperature, pH and the patterns of ocean currents may change the distribution areas of the characteristic species that define ecosystem types. So far these are future impacts where considerable uncertainty is associated with different scenarios. At present there is no empirical data with which to assess the extent of a reduction in area, or habitat quality, under different scenarios involving such changes.

The hydrothermal vents contain valuable minerals. Should extraction of these be permitted, it could lead to considerable habitat impact. Future extraction of minerals from inactive hydrothermal vents is under discussion and whether such an industry would commence activities in Norwegian waters is uncertain. At this stage, however, there is very little knowledge about inactive hydrothermal vents, and at the same time possible extraction may have considerable impact on habitats in the surrounded area that are dominated by sponge and soft-corals. Since the possibility of mineral extraction at hydrothermal vents in the future is, at present, a hypothetical threat, this has not been included in this assessment.

Existing knowledge

The most important existing knowledge for seabed systems has been the results from Mareano (Buhl-Mortensen et al. 2015), in particular the map of the distribution of vulnerable ecosystem types (www.mareano.no).

Detailed knowledge of the distribution of ecosystem types in deep waters is sparse from the time before modern mapping techniques with multibeam echosounders and high resolution visual information (e.g. mapping from Mareano and the K.G. Jebsen Centre for Deep Sea Research, University of Bergen). Consequently, for the majority of assessment entities there is no data which can be used as a basis for determining the reduction in area in the past 50 years. An exception is coral reef seabeds where destroyed coral reefs have not disappeared but remain in place and make it possible to estimate the extent of former areas. Interpretations of detailed maps from areas surveyed with multibeam echosounders are used to estimate the area of the total distribution of coral reef seabeds. Such maps make it possible to draw an outline and estimate the area of individual reefs. Figures for average reef size can thereby be used to estimate the total area.

The areas of marine sediment are estimated in classes that are harmonised with the NiN system, based on the sediments (grain size) map from NGU (presented by Mareano's mapping service: www.mareano.no ). Mareano covers only a small part of the Norwegian seabed, but if one assumes that the proportion of different sediments is representative, the total areas can be estimated. In coastal areas the composition of sediments differs from that on the continental shelf and very few areas have been mapped. This results in a very poor basis for estimating areas and a large amount of unrecorded data.

Most bedrock occurs along the coast and in fjord regions. It has not been surveyed sufficiently well to permit the presentation of reliable figures for area at either the major or minor ecosystem type level.

Tracking data from satellite surveillance (VMS-data) of fishing vessels can be used to provide an indication of the intensity of bottom trawling. Such data is quality assured by the Directorate of Fisheries and has been used in a series of studies investigating the relationship between the condition of the benthic community and the intensity of bottom trawling. In this assessment a comparison of bottom trawling intensities in the period 2009 – 2015 has been used to identify areas most severely impacted by bottom trawling.

Future requirements

Improved mapping of ecosystem types in deep waters is required in order to assess the condition of ecosystem types and biological communities. It has long been the prevailing view that ecosystem types in deep waters are largely homogenous and characteristed by muddy sediments. Recent research (e.g. Mareano and the K.G. Jebsen Centre for Deep Sea Research, University of Bergen) has nevertheless demonstrated that environment, bottom conditions and species composition can be extremely varied over short distances. There is a significant need to collect new data to enable the presentation of a realistic overview of the distribution of ecosystem types in deep waters. In addition to detailed bathymetric charts there is a need to collect: observation data (using ROV or an equivalent), fauna samples (to provide an accurate picture of species diversity and to correctly identify organisms observed in photos and video), and sediment samples to improve sediment maps. Furthermore, it is important to enhance the coarse oceanographic models that provide indications as to how the local ocean climate varies in terms of temperature, salinity, and the strength and direction of water currents close to the seabed. These factors are critical for being able to model the distribution of the organism community and ecosystem types.

Expert Committee

The members of the expert committee for Marine deep waters were Pål Buhl-Mortensen (chair), Torkild Bakken, Eivind Oug and Hans Tore Rapp.

References

Buhl-Mortensen L, Hodnesdal H, Thorsnes T (eds.) (2015). The Norwegian Sea Floor - New Knowledge from MAREANO for Ecosystem-Based Management.

Brattegard T, Holthe T (1997). Distribution of marine, benthic macro-organisms in Norway. Research Report for DN 1997-1. Directorate for Nature Management, p. 409.

Brattegard T, Holthe T, (2001). Distribution of marine, benthic macro-organisms in Norway. Research Report for DN 2001-3. Directorate for Nature Management.

Pedersen RB, Rapp HT, Thorseth IH, Lilley MD, Barriga F, Baumberger T, Flesland K, Fonseca R, Fruh-Green GL, Jorgensen SL (2010). Discovery of a black smoker vent field and vent fauna at the Arctic Mid-Ocean Ridge. Nature Communications 1:126.

Olsen BR, Økland IE, Thorseth IH, Pedersen RB, Rapp HT (2016). Environmental challenges related to offshore mining and gas hydrate extraction. Miljødirektoratet. Rapport M-532, 28 pp.

Oug E, Gjøsæter J, Anker-Nilssen T, Bakken T, Sneli J-A, Rueness J (2010). Marine miljø. Pages 13-25 in Kålås JA, Henriksen S, Skjelseth S, Viken Å (eds). Miljøforhold og påvirkninger for rødlistearter. Trondheim: Artsdatabanken. 

Oug E, Buhl-Mortensen P (2010). Koralldyr. In: Kålås JA, Viken Å, Henriksen S, Skjelseth S (eds.) (2010). Norsk rødliste for arter 2010. Artsdatabanken, Norway 191-198. 

Perez-Garcia C, Feseker T, Mienert J, Berndt C (2009). The Håkon Mosby mud volcano: 330 000 years of focused flow activity at the SW Barents Sea slope. Marine Geology 262: 105-115.