Lophelia reefs

04-07-2005
Researched byDr Harvey Tyler-Walters Refereed byDr Jason Hall-Spencer, Dr Alex Rogers, Prof. Paul Tyler & Dr Murray Roberts
EUNIS CodeA5.631 EUNIS NameCircalittoral Lophelia pertusa reefs

Summary

UK and Ireland classification

EUNIS 2008A5.631Circalittoral Lophelia pertusa reefs
EUNIS 2006A5.631Circalittoral Lophelia pertusa reefs
JNCC 2004SS.SBR.Crl.LopLophelia reefs
1997 BiotopeCOR.COR.LopLophelia reefs

Description

The cold-water coral Lophelia pertusa forms patches of bushy growths composed of a network of anastomosing branches that grow into thickets, coppices and eventually reefs under favourable conditions. The morphology and size of reefs are highly variable but reefs may be circular, dome-shaped or elongate, forming distinct patches or arranged in lines of 'islands' along the edges of the continental shelf, sea mounts, offshore banks and other raised sea bed features. Reefs may be composed of coral thickets 10 -50 m across and several metres high, mounds of 50 -500 m in diameter and 2 -33 m high, or through growth and/or fusion of nearby patches, form large elongate coral banks of up to 5 km in length and I km wide, reaching heights of ca 200 m and cover several square kilometres, depending on local conditions. In the Sula Ridge Norway, the coral grows in an iceberg furrow forming a coral bank 13 km in length, 300 m wide and 45 m high. Although Lophelia pertusa dominates, other cold-water corals may also occur, e.g. Madrepora oculata, Desmophyllum cristagalli, Dendrophyllia cornigera, Enallopsammia rostata and Solensmilia variabilis. The reef supports a species rich assemblage of invertebrates, especially suspension feeders such as foraminiferans, sponges, hydroids, gorgonians, corals, polychaetes, bryozoans, brachiopods, asteroids, ophiuroids, holothurians and ascidians. Relatively few species have so far been shown to be closely associated with Lophelia pertusa, for example, eunicid polychaetes, especially Eunice norvegica, and brittlestars, especially Ophiocantha species. The associated community requires further study. The xenophyophore Syringammina fragilissima (a giant protozoan growing up to 20 cm in diameter) occurs at markedly increased densities in downstream 'tails' of the some Lophelia mounds. [NB biotope description composed by author.]

Recorded distribution in Britain and Ireland

Reefs of Lophelia pertusa have been recorded on raised offshore seabed features from the Shetland-Faroe Basin, Rockall Bank and Rockall Trough, Anton Dohrn Seamount, Rosemary Bank, Hatton Bank, Bill Bailey's Bank, and the Wyville-Thomson Ridge in the north Atlantic off Britain, and in the Porcupine Seabight and Porcupine Basin off west Ireland. The map shows the recorded distribution of Lophelia pertusa, including isolated colonies as well as reefs.

Depth range

50-100 m

Additional information

The ecology of Lophelia pertusa (henceforth Lophelia) reefs is poorly studied and the biology or Lophelia poorly known. The following review is based primarily on the detailed review of Lophelia pertusa by Rogers (1999) with additional material from more recent studies. The author is grateful to the referees for their helpful comments and for highlighting additional information and recent findings.

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Habitat review

Ecology

Ecological and functional relationships

Rogers (1999) stated that the ecology of Lophelia pertusa reefs was poorly understood and remained largely un-investigated. The following information is inferred from a few studies of the fauna of Lophelia reefs in nature and aquarium studies (Jensen & Frederiksen, 1992; Rogers, 1999; Mortensen, 2001). Although the major groups of organisms are probably similar, the exact species present will vary with location.
  • Lophelia pertusa and other cold-water corals provide hard substrata for attachment of other epifaunal organisms, in the form of living and dead coral and coral fragments. The dense bushy growth of Lophelia locally modifies the environmental conditions (e.g. water flow) and provides a wide variety of niches for colonization by other species. Therefore, Lophelia may be regarded as an 'autogenic engineer' (Rogers, 1999) or key structural species.
  • Lophelia is a passive suspension feeder or passive carnivore, which has been observed to take zooplankton such as calanoid copepods and cumaceans in nature, and to take live zooplankton such as chaetognaths, small crustaceans (ca 1 mm e.g. copepods), and larger species such as krill ca 2 cm in length in aquaria (Mortensen, 2001; Mortensen et al., 2001). Mortensen (2001) demonstrated that Lophelia could also take a variety of foods, including dead food particles of krill, shrimp, herring and squid, and was able to reject unsuitable material including sediment. Mortensen (2001) concluded that Lophelia could utilize small organic particulates as food as well as live zooplankton. It probably also feeds on small invertebrates crawling over the coral surface.
  • The hard substratum provided by Lophelia, together with the strong currents in the areas it occupies, favours suspension feeding invertebrates, e.g. foraminiferans, sponges, hydroids, gorgonians (soft corals), corals, polychaetes, bryozoans, brachiopods, asteroids, ophiuroids, holothurians, and ascidians. For example, brittlestars, especially Ophiactis balli, were observed sheltering within the empty cups (calices) of dead corals with only their arms protruding (Rogers, 1999).
  • Mortensen (2001) suggested that there was a non-obligate mutualistic relationship between Lophelia and the polychaete Eunice norvegica, which shares a common distribution. In aquarium studies, Eunice norvegica was observed to steal food from the polyps of Lophelia, although Mortensen (2001) suggested that in nature Lophelia probably ingested live food before it could be stolen. Eunice norvegica was also observed to keep the coral surface clean of detritus and sedimentary particles, and in one instance attacked a sea urchin (Cidaris cidaris) that had climbed onto the coral. The polychaete may protect the coral from predators to some extent, a relationship seen in tropical coral communities (Mortensen, 2001). Most importantly, Eunice norvegica attaches its mucilaginous tube to the surface of the coral, which stimulates the coral to grow around and calcify the polychaetes' tube. This calcification may join adjoining coral branches, provide additional hard substrata for settlement of coral larvae and other invertebrates, and may strengthen the structure of the reef (Mortensen, 2001). In addition, tubes of the Eunice norvegica are capable of joining separate colonies, enhancing reef development, as seen in tropical corals (Dr Murray Roberts pers comm.).
  • The tubes of Eunice norvegica may also support other species of polychaete, e.g. the scale worm Harmothoe oculinarum.
  • Similarly, most bivalves were cavity dwellers occupying the empty calices of dead corals, e.g. Hiatella arctica and Acar nodulosa, while Delectopecten vitreus was found on the surface of live coral (Jensen & Frederiksen, 1992) and the giant file shell Acesta excavata may also use the coral as a substratum (Dr Jason Hall-Spencer pers comm.).
  • Jensen & Frederiksen (1992) observed only a few gastropods, the most numerous of which was Alvania jeffreysi, a predator of foraminifera. However, several species of gastropod have been recorded from Lophelia reefs (see Rogers, 1999), many of which are probably epifaunal grazers.
  • Many of the starfish and sea urchins recorded are probably epifaunal grazers and /or scavengers within the reef, while the mobile crustaceans including isopods, shrimp, crabs and hermit crabs are probably scavengers, or generalist predators of small invertebrates.
  • The coral skeleton may be eroded by several groups of organisms, e.g. bacteria, fungi, and sponges (e.g. Aka labyrinthica, Alectona millari and Cliona vastifera) which bore into dead corals, while eunicid, cirratulid, sabellid and spionid polychaetes also bore into the coral skeleton. Rogers (1999) noted that bioeroders play an important role in the development and maturation of coral reefs. Bioeroders reduce the coral skeleton to sediment, and weakens the coral structure so that pieces of coral break off or fall over. However, cavities produced by bioeroders also provide additional habitat complexity. Rogers (1999) noted that bioerosion in shallow coral reefs leads to rates of reef destruction that are only slightly slower than the rates of reef growth, so that any factor that reduces the growth rate of the corals may result in loss of the reef, especially since only a single cold-water coral species dominates this biotope.
  • Jensen & Frederiksen (1992) noted that many of the species they observed were only present as juveniles, suggesting that many species may use the Lophelia reef as a nursery area (Rogers, 1999).

Seasonal and longer term change

Lophelia reefs occupy relatively stable bodies of water (Rogers, 1999) but are still likely to experience seasonal fluctuations in current strength, temperature and food supply. The breaking of internal waves increases vertical mixing of the water column in areas of 'critical slope' (Frederiksen et al., 1997), which may occur close to the shelf break around the Faeroes Islands and the Faeroe-Shetland Channel interface (Roberts et al., 2003). Roberts & Anderson (2002a) noted that the polyps of Lophelia behaved asynchronously, without any clear diurnal patterns over a three day period in aquaria. Mortensen & Rapp (1998) detected distinct annual growth lines in Lophelia, and the growth of Lophelia from western Norway was carefully followed in aquaria over a 2.5 year period (Mortensen, 2001). Mortensen (2001) reported that linear extension of the skeleton was episodic, peaked in autumn, winter and spring, with a low growth period between June and September. In the aquaria, new polyps were generated mainly between August and December, the warmest part of the year, which suggested that temperature may be an important factor (Mortensen, 2001). However, deep-water population are probably not exposed to such temperature change. Mortensen (2001) observed no correlation between linear extension rates and temperature and salinity but concluded that the growth of the skeleton was correlated with seasonal variations in the abundance of particulate organic material and hence food availability.

The Lophelia reefs so far examined have been estimated to be extremely old, from several hundred to many thousands of years old. Therefore, although the longevity of individual coral polyps and associated species probably vary over time, the reef itself may be extremely long-lived (see 'time to reach maturity' below).

The associated fauna will probably exhibit seasonal fluctuations in abundance. For example, many bryozoan and hydroid species die back in the winter months. However, no other information was found.

Habitat structure and complexity

The shape and size of individual patches and reefs of Lophelia are highly variable, depending on local environmental conditions (Rogers, 1999). The density of branching varies and Lophelia may form robust 'bushes' in which the skeleton is thickened or finer more delicate branched colonies susceptible to damage e.g. from the pressure wave created by a submersible (Rogers, 1999). Reefs may be circular or 'halo-shaped', 'haystack-shaped', form domed mounds, or be elongated with one or more peaks, and the patches of reef may be arranged along the ridge of seamounts or banks in chains or 'islands groups' (Wilson, 1979a, b; Rogers, 1999; De Forges et al., 2000; Mortensen et al., 2001).

Wilson (1979b) suggested a model of Lophelia patch development, based on terms developed by Squires (1964), in which growth of an initial colony gives rise to coral fragments around it that either continue to grow or are colonized by Lophelia larvae. As the new colonies grow and merge they surround the central colony forming a 'thicket'. The central colony dies back, probably due to reduced water flow within the patch, and is reduced to coral debris, forming a halo shaped ring or 'coppice'. Subsequent phases of growth around the outside of the coppice results in concentric circles of growth forming a mature 'coppice' (see Wilson, 1979b for details). The reef becomes composed of several distinct zones, as exemplified by a Lophelia reef in the Stjernsund Fjord, Norway (Freiwald et al., 1997; Rogers, 1999). The living coral at the top of the reef grows on top of large fragments of dead coral, underneath which was a layer of small fragments and sediment. The living coral on top of the reef formed ring-shaped colonies as described by Wilson (1979b). Coral fragments from the main reef had also fallen down only to grow as spherical colonies. Away from the main reef Lophelia formed isolated coral thickets and dead collapsed frameworks (Rogers, 1999).

In the Darwin Mounds of the Rockall Trough, Masson et al. (2003) suggested that the mounds had preceded reef formation. In their study, Masson et al. (2003) observed no stratification of coral fragments in cores of the mounds, the cores being composed of quartz sand rather than bioclastic sediment. They concluded that mounds were formed by the deposition of sediment on the surface of the seabed by fluid escapes from the seafloor, and subsequently colonized by Lophelia and its associated fauna. The mounds form a raised substratum, which is a preferred habitat for Lopheliaand other suspension feeders (Masson et al., 2003).

The network of living and dead coral branches provide niches for a variety of organisms, e.g. bivalves and brittlestars within dead coral cups, and eunicids within and between the branches of corals (see above). However, the majority of the fauna observed were within and on the dead coral and coral debris (Rogers, 1999). Some coral mounds form acoustically detectable 'tails' aligned with the prevailing current, e.g. in the Darwin Mounds 'tails' included high densities of the giant protozoan Syringammina fragilissima (Masson et al., 2003).

Productivity

Frederiksen et al. (1997) suggested that Lophelia reefs on the continental slopes off Norway, west Scotland and the Faroes, occupy a depth at which tidal currents impinge on raised seabed features with a critical degree of slope to generate internal waves. The resultant mixing of the water column above the shelf break generates nutrient rich surface waters, that in turn promotes phytoplankton productivity. Similarly, the increased mixing of bottom waters leads to resuspension of organic particulates from the seabed. Both effects can potentially increase the supply of food to Lophelia and other suspension feeders (Rogers, 1999). Rogers (1999) also noted that the massive reef complex on the Sula Ridge, off Norway was thought to rely on the supply of zooplankton from fertile surface waters. The occurrence of some Lophelia reefs in the vicinity of light hydrocarbon or methane seeps has led to the hypothesis that Lophelia reefs and their associated fauna may be supported by a chemosynthetic food chain (Hovland & Thomsen, 1997; Hovland, et al., 1998). But Rogers (1999) concluded that the evidence was equivocal. For example, occurrences of Lophelia in the Rockall Bank and elsewhere are not associated with hydrocarbon seeps (Rogers, 1999). Analysis of stable radiocarbon isotope (13C) levels in the skeleton of Lophelia pertusa and 13C/12C ratios in tissue is not consistent with a food chain based on hydrocarbon seeps (see Rogers, 1999 and Roberts et al., 2003 for discussion). Rogers (1999) suggested that most of the hydrocarbons are utilized by other organisms at the sediment-water interface.

Although, the only living part of the Lophelia framework are the surface colonies, the skeletal framework provides substratum, interstices, refugia and feeding grounds for a wide variety of other organisms. Most of the biomass of the reef is provided by the associated fauna, especially in smaller reefs (Rogers pers comm.). Overall, Lophelia reefs are probably highly productive ecosystems (secondary productivity) but no direct information was found. Lophelia reefs probably exhibit tight coupling between the pelagic and benthic ecosystems (Dr Murray Roberts, pers comm.).

Recruitment processes

Colonies of Lophelia grow by intratentacular budding, the division of an existing polyp into two polyps (Cairns, 1979; Rogers, 1999). In addition, Lophelia may generate new colonies by fragmentation, whereby coral fragments fall or are broken off, and continue to grow under suitable conditions. Fragmentation is a major mechanism whereby the initial colony expands to form a coppice and ultimately a reef (see 'habitat complexity' above and Wilson, 1979b). Some corals can reproduce by parthenogenesis, the development of an un-fertilized egg, while others exhibit 'polyp bailout' in which a polyp or piece of coral tissue leaves its skeleton, and moves to a suitable substratum and secretes a new skeleton (Richmond, 1997). However, there is currently no evidence for the existence of parthenogenesis or 'polyp bailout' in Lophelia (Rogers, 1999).

The mechanism of sexual reproduction in Lophelia pertusa is unknown (Rogers, 1999). About 25% of coral species have separate sexes while the majority are hermaphrodite, i.e. possess both male and female reproductive organs. In some species fertilization occurs externally and eggs and sperm are spawned into the sea. In other species fertilization occurs internally and the larvae develop and are brooded within the parent colony (Richmond, 1997). The larva of corals is the ciliated planula larvae. In species studied, the externally fertilized planula has been calculated to remain competent and capable of recruitment for 3-4 weeks. Brooded planula larvae tend to have a longer competence period, e.g. estimated to be over 100 days in Pocillopora damicornis (Richmond, 1997). The prolonged competency period is attributed to the provision of symbiotic zooxanthellae in brooded planulae that supplement larval energy reserves (Richmond, 1997). Cold-water corals, such as Lophelia, lack zooxanthellae, however Roberts (2002a) noted that larval competency in cold temperate waters may be considerably longer than observed in tropical waters.

The planula larvae of Lophelia pertusa require hard substrata for settlement, including rock surfaces, artificial substrata, coral fragments or hydrocarbon seep associated carbonates. In sedimentary areas, Lophelia pertusa may settle on hard substrata as small as a shell, pebble, or worm tube (Rogers, 1999). However, a hard substratum is a pre-requisite for settlement and a layer of sediment may interfere with settlement and hence recruitment.

Whilst Rogers (1999) noted that there was no indication of the dispersive capability of Lophelia pertusa, its ability to colonize isolated hard substrata and artificial substrata such as submarine cables, the Brent Spar storage buoy and oil rigs suggests that it has a pelagic larval phase (Rogers, 1999; Roberts, 2002a). Roberts (2002a) concluded that the occurrence of Lophelia on structures in the Beryl and Brent oil fields in the North Sea was good evidence for a dispersive planula larva. Roberts (2002a) suggested that the colonies in the North Sea oil fields originated as larvae from the offshore banks of the Atlantic margin, and were carried into the North Sea in cooled Atlantic water, possibly via the east Shetland Atlantic Inflow current. Transport of larvae in the water mass of prevailing water currents probably provides the opportunity for long distance dispersal.

The recent evidence (above) suggests that larvae are dispersive but that migration is not sufficient to counteract reproductive isolation of populations (Dr Alex Rogers pers comm.). Molecular genetic data is somewhat confused at present but microsatellite data indicates that Beryl oil fields samples of Lophelia are closely related to northern Rockall Trough populations and that there is strong genetic differentiation (population sub-division), with very low gene flow between areas (Dr Alex Rogers pers comm.). Present evidence suggests that asexual reproduction predominates in reef growth and that the contribution from larvae may be limited. Therefore, molecular genetic data suggests that recolonization of a disturbed areas is likely to be slow (Le Goff-Vitry & Rogers, 2002, summary only, Dr Alex Rogers pers comm.).

The associated epifauna and interstitial fauna probably depend on locality and recruit from the surrounding area. Many hydroids, ascidians and probably sponges have short lived planktonic or demersal larvae with relatively poor dispersal capabilities. Exceptions include Alcyonium digitatum and hydroids that produce medusoid life stages and probably exhibit relatively good dispersal potential. Hydroids are opportunistic, fast growing species, with relatively widespread distributions, which colonize rapidly and are often the first groups on species to occur on settlement panels. Sponges may take longer to recruit to the habitat but are good competitors for space. Recruitment in epifaunal communities is discussed in detail in the faunal turf biotopes MCR.Flu, CR.Bug and in Modiolus modiolus beds (MCR.ModT). Mobile epifaunal species, such as echinoderms (starfish and brittlestars), crustaceans, and fish are fairly vagile and capable of colonizing the community by migration from the surrounding areas. In addition, most echinoderms and crustaceans have long-lived planktonic larvae with potentially high dispersal potential, although, recruitment may be sporadic, especially in echinoderms.

Time for community to reach maturity

Mortensen et al. (2001) suggested that the size of Lophelia reefs was determined by the time taken for development and the topography of the seabed that affects both the area over which coral fragments and rubble can spread and the local currents and hence, food supply and growth rates.

The growth rate of Lophelia is very slow. Estimates of growth rate range from 2 to 25 mm/yr. depending on location (Wilson, 1979b; Rogers, 1999; Hall-Spencer et al., 2002; Roberts, 2002a) although inaccurate sampling of the coral skeleton may have led to biased estimates. Studies of growth lines suggested a mean extension rate of 5.5 mm/yr., with linear extension rates greatest in the early stages of polyp growth, slowing with age (Mortensen & Rapp, 1998). Measurement of linear extension rates in aquarium specimens gave a mean annual growth rate of 9.4 mm/yr. (Mortensen, 2001). Rates of growth on artificial structures were estimated to range from 6 mm/yr. on submarine cables in north west Spain to 26 mm/yr. on the Brent Spar storage buoy (Bell & Smith, 1999; Roberts, 2002a).

Estimates of potential age of Lophelia colonies and reefs vary with location and with the growth rates estimates used to calculate age. For example, Wilson (1979b) estimated that a single colony 1.5 m in height would probably be 200 -366 years old (based on a growth rates between 7.5 and 4.1 mm/yr. respectively). Lophelia reefs sampled off Norway, 25 m in height and 330 x 120 m in area were probably between 1,000 and 6,250 years old, depending on growth rate (Rogers, 1999). Radiocarbon dating of cold-water corals from west Ireland, provided estimated ages of 451 years before present (BP) for live Lophelia pertusa and 762 years BP for dead Lophelia pertusa fragments (Hall-Spencer et al., 2002). However, dead coral rubble formed by the cold-water coral Desmophyllum cristagalli, at the same site, were between 4067 and 5001 years BP, which suggested that the reef system was probably at least 4,500 years old (Hall-Spencer et al., 2002). The age of Lophelia reefs in south east Norway and west of Fedje Island, west Norway was estimated to be 8,700 and 3,600 years BP respectively (Mikkelsen et al., 1982; Rokoengen & Østma, 1985; Mortensen et al., 2001). The Lophelia reefs of the Sula Ridge were estimated to be 8,600 years old, having developed over the last 10,000 years since the last ice age (Hovland & Mortensen, 1999; Mortensen et al., 2001). Coral rubble from cold-water coral reefs on the Florida Hatteras slope, which was not ice covered, had an age of ca 20,230±230 years BP (Mortensen et al., 2001).

Recruitment to available hard substrata by epifauna such as hydroids, and ascidians is probably fairly rapid (see MCR.Flu or CR.Bug), with sponges and soft corals taking longer to develop. Bryozoans, hydroids, and ascidians are opportunistic, grow and colonize space rapidly and will probably develop a epifaunal cover within 1-2 years (for example see Sebens, 1985, 1986). Mobile epifauna and infauna will probably colonize rapidly from the surrounding area. Slow growing species such as some sponges and anemones (see Sebens, 1985, 1986), will probably take many years to develop significant cover, so that a diverse community may take up to 5 -10 years to develop, depending on local conditions.

While, epifaunal and infaunal species would colonize relatively rapidly, the key species determining the development of the reef is Lophelia itself. Deep-sea communities are thought to have very slow colonization rates (Rogers, 1999). While Lophelia may have a dispersive larval stage (see Roberts, 2002a), there is little information available on recruitment rates in natural systems. However, recent molecular genetic data suggests that larval recruitment is probably low or sporadic (Le Goff-Vitry & Rogers, 2002, summary only; Dr Alex Rogers, pers comm.). Overall, even with good recruitment, Lophelia is very slow growing and would probably take several hundred years to develop large colonies (ca 1.5-2 m in diameter) and several thousand years to develop a reef system 10 -30 m thick (Fosså et al., 2002).

Additional information

None entered.

Preferences & Distribution

Recorded distribution in Britain and IrelandReefs of Lophelia pertusa have been recorded on raised offshore seabed features from the Shetland-Faroe Basin, Rockall Bank and Rockall Trough, Anton Dohrn Seamount, Rosemary Bank, Hatton Bank, Bill Bailey's Bank, and the Wyville-Thomson Ridge in the north Atlantic off Britain, and in the Porcupine Seabight and Porcupine Basin off west Ireland. The map shows the recorded distribution of Lophelia pertusa, including isolated colonies as well as reefs.

Habitat preferences

Depth Range 50-100 m
Water clarity preferences
Limiting Nutrients
Salinity Full (30-40 psu)
Physiographic Open coast
Biological Zone
Substratum Bedrock
Tidal
Wave
Other preferences Oceanic water

Additional Information

Distribution
Lophelia pertusa has been recorded globally from the North Atlantic, parts of the Mediterranean, along the coasts of west Africa, the United States, east Canada and around the mid Atlantic islands south to Tristan da Cunha. It is also recorded from the Pacific, southern California, Cobb Seamount, and from the Island of St Paul in the Indian Ocean. There is also a single record from the Macquarie Ridge, south of New Zealand (Rogers, 1999). However, records often refer to dead or subfossil remains, may not represent reefs in all cases, and Lophelia often occurs as isolated patches over large areas of seabed, making it difficult to detect. Therefore, its living distribution may be inaccurate (Rogers, 1999). Recent genetic evidence suggests that Brazilian records of Lophelia are genetically distinct and may represent a different species or sub-species (Le Goff-Vitry et al., in press; Dr Alex Rogers, pers comm.).

Lophelia pertusa has been recorded from the continental shelf of the north east Atlantic more frequently than any other place in the world (Rogers, 1999). In addition, to records in British and Irish waters, Lophelia reefs have also been recorded from Norwegian fjords, and on raised offshore seabed features from Haltenbanke, Froyabanken and the Sula Ridge in south and west Norway, the Faroes shelf, and from the Porcupine Basin south along the continental shelf edge to North Africa (Rogers, 1999; ICES, 2002; Roberts, 2002b; A. Grehan pers. comm.). Scattered records also occur in the North Sea, the Outer Hebrides, Stanton Bank, and Donegal Basin (Rogers, 1999; Roberts et al., 2003). A review of the distribution of cold water coral in European waters is provided by Zibrowius (1980) and a detailed list of records is presented by Rogers (1999).

Habitat preferences
  • Lophelia pertusa requires hard substrata (e.g. rock, coral fragments, artificial substrata, or hydrocarbon seep associated carbonates) on which to settle. Colonies that occur in sedimentary habitats have settled on small pieces of hard substrata such as pebbles, shells or worm tubes (Rogers, 1999).
  • Lophelia pertusa appears to prefer the presence of oceanic waters. For example, Lophelia only occurs in Norwegian fjords that allow deep oceanic water into the fjord; its upper limit determined by the depth of coastal waters (Rogers, 1999).
  • Its preference for oceanic waters suggested that Lophelia was sensitive to salinity and temperature (Rogers, 1999). Lophelia pertusa is found in water between 4 and 12 °C (Rogers, 1999) but records from the Mediterranean suggest it can survive up to 13 °C (Mortensen, 2001). Rogers (1999) noted that Lophelia is not usually found in waters colder than 6 °C but that it may encounter lower temperatures at the lower limits of its depth range. In a recent study, Roberts et al. (2003) noted a strong correlation between the occurrence of Lophelia and temperature. With a single exception, Lophelia had not been recorded in waters colder than 4 °C and was absent from depths of greater than 500 m in the Faeroe-Shetland Channel, presumably due to the influence of cold Nordic waters (e.g. the Arctic Intermediate Water and/or Norwegian Sea Arctic Water with temperatures of 1 -5 °C or -0.5 to 0.5 °C respectively) (Roberts et al., 2003). The only record of Lophelia in the Faeroe-Shetland Channel below 500 m occurred in an area subject to temperatures below 4 °C for 52% of a 10 month period of observations and below zero for 4% of the same period (Bett, 2000). Roberts et al. (2003) suggested that the above record probably represented the limit of Lophelia pertusa's range but that present evidence suggested that seabed mounds associated with coral growth were unlikely at depths influenced by cold Nordic waters.
  • Lophelia pertusa occurs in waters of 35 -37 psu but in fjords tolerates salinities as low as 32 psu (Rogers, 1999; Mortensen et al., 2001).
  • The upper limit of Lophelia in fjords corresponds to the position of the thermocline (Rogers, 1999). However, Frederiksen et al. (1992) considered the origin of the water masses to be more important, while Mortensen et al. (2001) suggested that the pycnocline between lower salinity, warmer coastal waters and deeper, cooler oceanic water resulted in more stable conditions within the fjords, and a strong influx of oceanic waters.
  • The upper limit of Lophelia in oceanic waters is probably seen on oil platforms in the North Sea. Lophelia pertusa was reported growing on single point moorings of the Beryl Alpha platform between depths of 75 and114 m (Roberts, 2002a). The water column around the platform was stratified; the salinity varied from 34.8 ppt at the surface to just over 35 ppt at 50 m, while the surface temperature remained fairly constant at 11.5 °C to a depth of 50 m before dropping rapidly to 8 °C between 70 and 110 m (Roberts, 2002a). Roberts (2002a) noted that the depth of Lophelia corresponded with 8 °C and a salinity of 35 ppt. He suggested that Lophelia was restricted to depths of greater than 70 m by the physical conditions, competition from other epifauna (e.g. sponges and sea anemones) and possibly by wave action during storms (Roberts, 2002a).
  • Strong current flow appears to be required for growth in Lophelia, which occurs in areas of strong water flow. Lophelia reefs occur where the topography causes current acceleration, e.g. on raised seabed features such as seamounts and banks and where the channel narrows in Norwegian fjords (Rogers, 1999). For example, soft corals were reported to reach higher densities near the peaks of seamounts rather than the slopes, or along the edges of wide peaks (see Rogers, 1999). Frederiksen et al. (1992) suggested that topographical highs create internal waves, depending on slope, that resuspended organic particulates from the seabed, and increase the flux of nutrient-rich waters to the surface waters increasing phytoplankton productivity; both effects resulting in increased food availability for Lophelia and other suspension feeders.
  • Water flow is important for suspension feeders and passive carnivores, such as Lophelia, to provide adequate food, oxygen and nutrients, to remove waste products and prevent sedimentation, however, the optimum current speed varies with species (see Hiscock, 1983 for discussion). For example, Mortensen (2001) observed no polyp mortality in the vicinity of his aquaria inlets but high mortality at the opposite end. Similarly, the death of coral polyps within a coral coppice is thought to be due to reduced water flow within the colony (Wilson 1979b). Mortensen (2001) also noted that high current flow (greater than ca 0.05 m/s) was detrimental to growth, presumably due to reduced food capture rates. Frederiksen et al. (1992) suggested that Lophelia reefs around the Lousy and Hatton Banks would typically encounter currents speeds of 0.01 -0.1 m/s. Water flow rates >0.4 m/s were recorded by moored and landed deployed current meters close to deep-water coral mounds in the Porcupine Seabight (White , 2001 cited in Grehan et al., 2003), while Masson et al. (2003) recorded a maximum residual bottom water flow of 0.35 m/s over a 20 day period in July 2000 over the Darwin Mounds. Food availability may be of greater importance than current speed alone.
  • Around the Norwegian /Scottish Shelf and Faroes, Lophelia most commonly occurs at depths between 200 -400 m, and between 200 -1000 m in the Massifs off west Ireland and the Bay of Biscay, and in some records extends to 3000 m (Rogers, 1999). Rogers (1999) suggested that its deepest limit may coincide with the oxygen minimum zone.
  • In deep waters the upper limit of Lophelia is probably controlled by the transition from oceanic to coastal or surface waters (see Rogers, 1999). However, Lophelia reefs occur as shallow as 50 m in Norwegian fjords. Frederiksen et al. (1992) suggest that its upper limit is controlled by wave action. Draper (1967) noted that wave periods in offshore areas are generally of longer than in enclosed seas and therefore penetrate to greater depths. However, Draper (1967) estimated that as far out as the continental shelf, for one day a year, storm conditions could generate a oscillatory water movement on the seabed of only ca 0.4 m/s at 180 m. Wave mediated currents are oscillatory and possibly more likely to result in damage to rigid corals than water flow (see Hiscock, 1983), although their skeletons are quite robust (Dr Jason Hall-Spencer pers comm.). In Norwegian fjords where Lophelia reefs occur as shallow as 50 m, wave action is slight at the surface and most likely does not penetrate more than a few tens of metres. Inner fjords have limited fetch so that wave action is unlikely to penetrate to more than a few tens of metres even in storm conditions (Dr Keith Hiscock pers. comm.). Rogers (1999) noted that the upper limit of Lophelia in the Norwegian fjords also coincided with the thermocline, and that the turbidity of the coastal surface water also reduced competition from algae.
  • It has been suggested that Lophelia reefs are associated with hydrocarbon or methane seeps (Hovland & Thomsen, 1997; Hovland, et al., 1998). But Rogers (1999) concluded that the evidence was equivocal. For example, occurrences of Lophelia in the Rockall Bank and elsewhere are not associated with hydrocarbon seeps (Rogers, 1999). Analysis of stable radiocarbon isotope (13C) levels in the skeleton of Lophelia pertusa and 13C/12C ratios in tissue is not consistent with a food chain based on hydrocarbon seeps (see Rogers, 1999 and Roberts et al., 2003 for discussion). Rogers (1999) suggested that most of the hydrocarbons are utilized by other organisms at the sediment-water interface. However, in some locations the hydrocarbon seep associated carbonates may provide hard substrata for settlement in an otherwise sedimentary habitat.
Overall, Lophelia reefs require hard substrata, the presence strong currents and a good food supply, usually associated with raised seabed features, banks and sea mounts. Lophelia occupies a relatively narrow range of temperatures (stenothermal) and salinity (stenohaline), although its upper limit may be determined by a number of factors.

Species composition

Species found especially in this biotope

Rare or scarce species associated with this biotope

-

Additional information

Rogers (1999) collated species lists from all previous studies of Lophelia reefs in the north-east Atlantic and noted that about 886 species had been recorded, although this number of species is probably an under-estimate. Diverse species groups include the Foraminifera, Polychaeta, Echinodermata, and Bryozoa. The diversity of polychaetes, echinoderms and bryozoans recorded from Lophelia reefs is similar to that found on shallow water tropical coral reefs (Rogers, 1999). However, Scleractina (corals), Mollusca and Pisces (fish) have relatively low diversities compared to tropical reefs (see Rogers, 1999). Jensen & Frederiksen (1992) suggested that most species present were not strongly associated or endemic to the Lophelia reefs they studied, however the associated community is still poorly understood (Rogers, 1999). Recent studies of the fauna of coral-water coral reefs on seamounts off Tasmania by Koslow et al. (2001) recorded 262 species of invertebrates of which 24 -43% were new to science and 16 -33% were restricted to the seamount environment, while De Forges et al. (2000) recorded 850 species of mega and macrofauna of which 29 -34% were new to science and were potential seamount endemics. Overall, cold water coral reefs represent biodiversity hot spots within their area. For example, Masson et al. (2003) reported that initial studies suggested that invertebrate density was about 2-3 times higher on the Darwin Mounds than the surrounding sediments. Further study is required to estimate the biodiversity of northeast Atlantic Lophelia reefs and seamounts.

Sensitivity reviewHow is sensitivity assessed?

Explanation

Lophelia pertusa grows into dense bushes, coppices, thickets and, under favourable conditions, large reefs. The coral skeleton provides additional hard substratum in the form of living and dead coral, and coral sediment. The reefs provides a variety of niches for other organisms within the coral matrix but especially within the dead coral fragments and underlying sediment (see Rogers, 1999). Therefore, Lophelia is regarded as an 'autogenic engineer' or 'ecosystem engineer'. Eunice norvegica builds its tubes within the coral matrix, which are subsequently calcified by the coral, strengthening the matrix. Eunice norvegica may exhibit a non-obligate mutualistic relationship with Lophelia (see ecosystem relationships) (Mortensen, 2001) and is probably an important functional species. The biology of Lophelia is poorly known, so no review of the species has been prepared. Relevant information on its biology has been included in the sensitivity assessment where possible.

The ecological relationships between Lophelia and its associated community are poorly understood (Rogers, 1999) and no characterizing species (sensu Connor et al., 1997a) have so far been identified.

Species indicative of sensitivity

Community ImportanceSpecies nameCommon Name
Important functionalEunice norvegicaA bristleworm
Key structuralLophelia pertusaA cold-water coral

Physical Pressures

 IntoleranceRecoverabilitySensitivitySpecies RichnessEvidence/Confidence
High Very low / none Very High Major decline High
Removal of the substratum would result in removal of living coral and dead coral debris, resulting in destruction of the reef and loss of the biotope. Therefore an intolerance of high has been recorded. Recovery would probably take several hundreds to thousands of years (see additional information below).
Low Very high Very Low No change Very low
Rogers (1999) suggested that Lophelia pertusa would be intolerant of increased rates of sedimentation (siltation), caused by decreased water flow, or the resuspension and subsequent sedimentation of sediment by marine activities, such as offshore construction or mobile fishing gear (e.g. beam or otter trawls), or the discharge of drill cuttings. Corals are generally thought to be intolerant of increases in sedimentation which is thought to be one of largest sources of degradation of coral reefs (Norse, 1993) and may suppress the growth rates of colonies (Fosså et al., 2002). Rogers (1999) suggested that sedimentation rates of >10 mg/cm²/day in shallow water coral reefs were high. Smothered polyps would be expected to starve. Mortensen (2001) reported that 25-100% of polyps died after being starved for 3 months or more but in some cases polyps survived starvation for 16 and 20 months. Preliminary results suggest that sand deposition rates of 0.1 mg/cm²/min significantly reduced polyp expansion in Lophelia pertusa (Roberts & Anderson, 2002b), which would reduce feeding and hence growth rates. However, Mortensen (2001) demonstrated that Lophelia pertusa was able to remove sediment particles <3 mm within 3-5 min and 3-5 mm particles within ca 15 min due to beating of cilia towards the tips of the tentacles, and reported that the living coenosarc (coral tissue) was always clean of sediment. Earlier studies by Shelton (1980), showed that Lophelia pertusa could remove graphite particles within ca 30 sec. Similarly, Reigl (1995) demonstrated that scleractinian corals were able to clean sand from their surface actively when exposed to 200 mg of sand per cm² in a single application clearing 50% of the sand within 1000 min, and all the species studied survived for 6 weeks continuous exposure to 200 mg of sand per cm². Reigl (1995) concluded that corals could cope with considerable amounts of sand deposition. Nevertheless, Rogers (1999) suggested that an increase in sedimentation is likely to interfere with feeding and hence growth, which would alter the balance between growth and bioerosion, potentially resulting in degradation of the reef. In addition, smothering would prevent settlement of larvae and hence recruitment.

At the benchmark level (smothering by 5 cm of sediment for a month) the majority of the Lophelia pertusa polyps would probably be unaffected due to the size of the colony, which is raised above the seabed. Similarly, most other suspension feeding invertebrates will probably survive for one month, suggesting an overall intolerance of low. Recovery would probably be rapid once the sediment was removed.

However, any activity that reduces growth may have detrimental effects on the survival of Lophelia colonies and the reef in the long term. Lophelia reefs are probably highly intolerant of prolonged or frequent smothering effects.
Low Very high Very Low No change Low
Increased suspended sediment levels may interfere with feeding in suspension feeders, including Lophelia pertusa, and hence growth (see above). Therefore an intolerance of low has been recorded at the benchmark level. Recovery would probably be rapid.
Low Very low / none Moderate Minor decline Moderate
Lophelia occurs in areas of strong currents, where internal waves and current acceleration provides adequate food supplies in the form of plankton and suspended organic particulates. Therefore, any activity that decreased the level of suspended particulates may reduce the food available to Lophelia and other suspension feeders. Rogers (1999) suggested that any interference with feeding and hence growth, may alter the balance between growth and bioerosion, potentially resulting in degradation of the reef. However, at the benchmark level duration of one month, decrease in food availability is likely to have only short term effects. Therefore, an intolerance of low has been recorded. Recovery would probably be rapid.
Not relevant Not relevant Not relevant Not relevant Not relevant
Cold-water corals and other subtidal epifauna are most probably highly intolerant of desiccation and aerial exposure. However, deep-water corals are extremely unlikely to be exposed to the air and not relevant has been recorded.
Not relevant Not relevant Not relevant Not relevant Not relevant
Lophelia reefs occur in oceanic waters, at depths of over 200 m, except in Norwegian fjords where it upper depth limit may be 50 m, below the influence of coastal waters. Therefore, it is unlikely to be affected by changes in the emergence regime and not relevant has been recorded.
Not sensitive* Not relevant
Lophelia reefs occur in oceanic waters, at depths of over 200 m, except in Norwegian fjords where it upper depth limit may be 50 m, below the influence of coastal waters. Therefore, it is unlikely to be affected by changes in the emergence regime and not relevant has been recorded.
Low Very high Very Low Minor decline Low
Strong current flow appears to be required for growth in Lophelia, which occurs in areas of strong water flow. Lophelia reefs occur where the topography causes current acceleration, e.g. on raised seabed features (e.g. seamounts and banks) and where the channel narrows in Norwegian fjords (Rogers, 1999). Frederiksen et al. (1992) suggested that topographical highs create internal waves, depending on slope, that resuspended organic particulates from the seabed, and increase the flux of nutrient-rich waters to the surface waters increasing phytoplankton productivity; both effects resulting in increased food availability for Lophelia and other suspension feeders. Water flow is important for suspension feeders and passive carnivores, such as Lophelia, to provide adequate food, oxygen and nutrients, to remove waste products and prevent sedimentation but the optimum current speed varies with species (see Hiscock, 1983 for discussion). For example, Mortensen (2001) observed no polyp mortality in the vicinity of his aquaria inlets but high mortality at the opposite end. Similarly, the death of coral polyps within a coral coppice is thought to be due to reduced water flow within the colony (Wilson, 1979b). Mortensen (2001) also noted that high current flow (greater than ca 0.05 m/s) was detrimental to growth, presumably due to reduced food capture rates. Frederiksen et al. (1992) suggested that Lophelia reefs around the Lousy and Hatton Banks would typically encounter currents speeds of 0.01-0.1 m/s. Water flow rates >0.4 m/s were recorded by moored and landed deployed current meters close to deep-water coral mounds in the Porcupine Seabight (White , 2001 cited in Grehan et al., 2003), while Masson et al. (2003) recorded a maximum residual bottom water flow of 0.35 m/s over a 20 day period in July 2000 over the Darwin Mounds. The mass movement of water and food availability may be of greater importance than current speed alone.

Currents speeds of 0.01 -0.1 m/s, 0.35 or 0.4 m/s approximate to between weak and moderately strong water flow. However, oceanic and tidal currents in the region of the Faroes were reported to be about 0.5 m/s (moderately strong) and in the region of west Shetland 0.5 -0.7 m/s or more (moderately strong). Although this species occurs in areas subject to moderately strong current and mass water movement, Mortensen's data (2001) suggests that increased flow may reduce growth. Therefore, an increase in water flow from moderately strong or strong to very strong for a year may depress growth due to reduced feeding efficiency. But, given the long-lived nature of Lophelia colonies, an increase in water flow for one year is probably tolerable and an intolerance of low has been recorded, albeit with low confidence. Other epifaunal species may be swept away in very strong water flow although the Lophelia coral matrix would probably provide a refuge, however, some species may be lost and species richness decline.

Tolerant Not sensitive* Not relevant
Strong current flow appears to be required for growth in Lophelia, which occurs in areas of strong water flow. Lophelia reefs occur where the topography causes current acceleration, e.g. on raised seabed features (e.g. seamounts and banks) and where the channel narrows in Norwegian fjords (Rogers, 1999). Frederiksen et al. (1992) suggested that topographical highs create internal waves, depending on slope, that resuspended organic particulates from the seabed, and increase the flux of nutrient-rich waters to the surface waters increasing phytoplankton productivity; both effects resulting in increased food availability for Lophelia and other suspension feeders. Water flow is important for suspension feeders, such as Lophelia, to provide adequate food, oxygen and nutrients, to remove waste products and prevent sedimentation but the optimum current speed varies with species (see Hiscock, 1983 for discussion). For example, Mortensen (2001) observed no polyp mortality in the vicinity of his aquaria inlets but high mortality at the opposite end. Similarly, the death of coral polyps within a coral coppice is thought to be due to reduced water flow within the colony (Wilson 1979b).

Therefore, a decrease in water flow from e.g. moderately strong to negligible for a year would probably result in death of at least a proportion of the coral polyps, depending on their position within the reef, i.e. polyps within the coral matrix would be more intolerant of. Other suspension feeding invertebrates would also be adversely affected. Decreased water flow would also result in a increase in siltation, potentially resulting in smothering of Lophelia and other suspension feeders, and potentially interfering with Lophelia recruitment (Rogers, 1999). Although, a change for a year (see benchmark) is probably only a short period of time in the life of a Lophelia colony, Mortensen (2001) observed polyp mortality within a short 2.5 yr. experiment. Therefore, an intolerance of intermediate has been recorded, albeit at low confidence. Recovery would probably take considerable time.

High Very low / none Very High Major decline Low
Lophelia pertusa is found in water between 4 and 12 °C (Rogers, 1999; Roberts et al., 2003) but records from the Mediterranean suggest it can survive up to 13 °C (Mortensen, 2001). In fjords the upper limit of the Lophelia reefs coincides with the level of the thermocline. Rogers (1999) suggested that death of the coral on the upper reaches of the reef may reflect changes in the depth of the thermocline. But the upper limit of the Lophelia reefs may be attributed to other factors, e.g. the origin of the water masses, salinity, wave action, or competition with other species e.g. sponges (Frederiksen et al., 1992; Rogers, 1999; Mortensen et al., 2001; Dr Alex Rogers, pers comm.). The requirement of Lophelia for oceanic waters suggested that Lophelia was probably intolerant of salinity and temperature change (Rogers, 1999). Lophelia pertusa was reported on single point moorings of the Beryl Alpha platform between depths of 75 and114 m (Roberts, 2002a). The water column around the platform was stratified; the salinity varied from 34.8 ppt at the surface to just over 35 ppt at 50 m, while the surface temperature remained fairly constant at 11.5 °C to a depth of 50 m before dropping rapidly to 8 °C between 70 and 110 m (Roberts, 2002a). Roberts (2002a) noted that the depth of Lophelia corresponded with 8 °C and a salinity of 35 ppt. He suggested that Lophelia was restricted to depths of greater than 70 m by the temperature and salinity, competition from other epifauna (e.g. sponges and sea anemones) and possibly by wave action during storms (Roberts, 2002a).

Offshore, deep-water Lophelia reefs are probably isolated from naturally occurring rapid acute changes in temperature due to their depth. But they are probably intolerant of an increase in temperature at the benchmark level caused by an activity that increases temperatures in their locality, e.g. from thermal discharges. The long term effects of climate change on deep-water currents could have far ranging effects (see water flow above). Therefore, an intolerance of high has been recorded.

Death of the coral polyps themselves would not immediately result in loss of the reef and the associated species. The associated species, especially epifauna would be lost over a period of years as the coral matrix was slowly eroded to coral rubble and eventually sediment. Although Lophelia may be able to colonize the substratum in the meantime, it would still take many years to replace the original reef (see additional information below).
High Very low / none High Major decline Low
Lophelia pertusa is found in water between 4 and 12 °C (Rogers, 1999). Rogers (1999) noted that Lophelia is not usually found in waters colder than 6 °C but that it may encounter lower temperatures at the lower limits of its depth range. In a recent study, Roberts et al. (2003) noted a strong correlation between the occurrence of Lophelia and temperature. With a single exception, Lophelia had not been recorded in waters colder than 4 °C and was absent from depths of greater than 500 m in the Faeroe-Shetland Channel, presumably due to the influence of cold Nordic waters (e.g. the Arctic Intermediate Water and/or Norwegian Sea Arctic Water with temperatures of 1-5 °C or -0.5 to 0.5 °C respectively) (Roberts et al., 2003). The only record of Lophelia in the Faeroe-Shetland Channel below 500 m occurred in an area subject to temperatures below 4 °C for 52% of a 10 month period of observations and below zero for 4% of the same period. Roberts et al. (2003) suggested that the above record probably represented the limit of this Lophelia pertusa's range but that present evidence suggested that seabed mounds associated with coral growth were unlikely at depths influenced by cold Nordic waters.

Offshore Lophelia reefs are probably isolated from naturally occurring rapid acute changes in temperature due to their depth but are probably intolerant of a decrease in temperature at the benchmark level. Any activity or event that changed the circulation of deep-water currents (e.g. climate change) could have wide ranging effects. Therefore, an intolerance of high has been recorded.

Death of the coral polyps themselves would not immediately result in loss of the reef and the associated species. The associated species, especially epifauna would be lost over a period of years as the coral matrix was slowly eroded to coral rubble and eventually sediment. Although Lophelia may be able to colonize the substratum in the meantime, it would still take many years to replace the original reef (see additional information below).
Tolerant Not relevant Not relevant No change Low
Offshore Lophelia reefs occur at considerable depth, below the photic zones of the temperate oceans, and hence in perpetual darkness. An increase in turbidity at the surface may decrease phytoplankton productivity. However, Lophelia and its associated suspension feeders utilize other sources of organic particulates and are unlikely to be significantly affected. Lophelia reefs may also occur at about 50 m in fjords, where an increase in turbidity may further inhibit algal growth, although the effects are unlikely to be significant. Therefore, not sensitive has been recorded.
Intermediate Very low / none No information Minor decline Low
Offshore Lophelia reefs occur at considerable depth, below the photic zones of the temperate oceans, and hence in perpetual darkness. A decrease in the turbidity of surface or deeper waters in unlikely to affect offshore reefs since light will still not penetrate to the depth occupied by Lophelia reefs. However, a decrease in turbidity may allow algae to colonize shallow Lophelia reefs in fjords, increasing competition for space with other suspension feeders and coral larvae, and potentially smothering the coral at its upper limit. Therefore, deep-water Lophelia reefs are probably not sensitive to a decrease in turbidity, while shallow water examples may be degraded, and an overall intolerance of intermediate has been recorded. Recovery would take many years (see additional information below).
Not relevant Not relevant Not relevant Not relevant Not relevant
Offshore Lophelia reefs occur, by definition, in extremely wave exposed conditions, although wave action is ameliorated by depth. Draper (1967) noted that wave periods in offshore areas are generally of longer than in enclosed seas and therefore penetrate to greater depths. However, Draper (1967) estimated that as far out as the continental shelf, for one day a year, storm conditions could generate a oscillatory water movement on the seabed of only ca 0.4 m/s at 180 m.

In Norwegian fjords where Lophelia reefs occur as shallow as 50 m, wave action is slight at the surface and most likely does not penetrate more than a few tens of metres. Inner fjords have limited fetch so that wave action is unlikely to penetrate to more than a few tens of metres even in storm conditions (Dr Keith Hiscock pers. comm.).

The oscillatory water movement generated by wave action could potentially result in fragmentation of branching coral skeletons at the upper limit of their depth distribution, although their skeletons are fairly robust. Occasional fragmentation may not unduly affect the reef but allow it to spread in the long term as the fragments continue to grow, or provide a substratum for colonization by Lophelia larvae. However, Lophelia occurs at depths at which even the wave action generated by storm conditions is unlikely to penetrate. Therefore, not relevant has been recorded.
Tolerant Not sensitive* Not relevant
In shallow, fjordic, examples of the biotope a decrease in wave action may allow the Lophelia reef to increase in height. The prevailing oceanic or tidal currents are probably far more important sources of water movement in areas occupied by Lophelia reefs than wave action alone. Therefore, a decrease in wave action is unlikely to have any detrimental effects and not sensitive has been recorded.
Tolerant Not relevant Not relevant Not relevant Low
Few marine invertebrates have been shown to respond to sound, although they do respond to pressure fluctuations similar to hydrodynamic water flow and currents. Close proximity to powerful sound sources, such as seismic survey arrays and underwater explosions will result in damage due to the pressure wave created, however, marine invertebrates are unlikely to be sensitive at the benchmark level (Vella et al., 2001). Fish species associated with the reef may temporarily avoid sites affected by noise from vessels but would probably return once the vessel has passed. Therefore, not sensitive has been recorded.
Not relevant Not relevant Not relevant Not relevant Not relevant
Offshore Lophelia reefs occur at great depth, below 200m, from very low light levels to perpetual darkness. Lophelia polyps showed no diurnal behaviour patterns in aquaria (Roberts & Anderson, 2002b) and have no known response to light or shading. Therefore, not relevant has been recorded.
High Very low / none Very High Major decline High
Although Lophelia reefs occur a great depths, they are likely to be subject to physical disturbance due to anchorage or positioning of offshore structures on the seabed but especially due to deep-sea trawling. Rogers (1999) suggested that trawling gear would break up the structure of the reef, fragment the reefs, and potentially result in complete disintegration of the coral matrix, and loss of the associated species.

Fosså et al. (2002) documented and photographed the damage caused to west Norwegian Lophelia reefs by trawling activity (see Fosså, 2003 for photographs). They reported that four, out of five sites studied, contained damaged corals. In the shallow regions of Sørmannsneset, only fragments of dead Lophelia were seen, spread around the site with no evidence of living colonies in the surrounding area, and Fosså et al. (2002) concluded that the colonies had been "wiped out". Overall, they estimated that between 30 and 50% of Lophelia reefs are either impacted or destroyed by bottom trawling in western Norway. Mechanical damage by fishing gear would also damage or kill the associated epifaunal species, and potentially turn over the coral rubble field, and modify the substratum (Rogers, 1999; Fosså et al., 2002). Fosså et al. (2002) demonstrated that gorgonian (horny) corals were also torn apart by bottom trawling. Fosså (2003) also note that fixed fishing nets, e.g. gill nets, and long-line fisheries and their associated anchors could potentially result in damage to the reefs such as breakage of the coral colonies. However, damage by long-line or gill net fisheries is probably of limited extent compared to bottom trawling (Fosså, 2003). Hall-Spencer et al. (2002) also provided photographic evidence of an area of reef impacted by bottom trawling, with a clearly visible trench (5 -10 cm deep) made by otter boards surrounded by smashed coral fragments in west Norway. Hall-Spencer et al. (2002) also noted that otter trawling with rockhopper gear damaged coral habitats in west Ireland, based on analysis of by-catch but also noted that fishing vessels actively avoided rough ground and that the majority of trawls did not result in Lophelia by-catch. Koslow et al. (2001) reported that on shallow, heavily fished seamounts off Tasmania, trawling had effectively removed the dominant cold-water coral and its associated fauna. The substratum of heavily fished seamounts was primarily bare rock or coral rubble and sand, features not seen on any lightly fished or un-fished seamount. The abundance and richness of benthic fauna was also "markedly reduced" on heavily fished seamounts (Koslow et al. (2001).

Overall, there is significant evidence of damage to Lophelia and other cold-water coral reefs due to deep-sea trawling, and an overall intolerance of high has been recorded. Recovery would probably take several hundreds to thousands of years (see additional information below).

Intermediate Very low / none High Decline Low
Some fragmentation of the coral skeleton is probably a natural part of the development of the reef system. Similarly, if large pieces of coral were removed to a new location, as long as the new are was suitable for growth, the coral would probably survive and continue to grow. Pieces of the coral reef transported by trawls or by-catch returned to the sea, may also survive if it was transplanted to a suitable area for growth, potentially forming a new coral coppice or reef in time (see Rogers, 1999), although survival is probably very limited (Dr Alex Rogers, pers comm.). Mortensen (2001) reported that 50% of the polyps of Lophelia, sampled by dredge and transported to aquaria remained closed for up to 3 weeks, while in samples collected by grab, the polyps opened within a few hours. Therefore, displacement is likely to result in an energetic cost and stress to the coral. However, the associated epifauna and infauna are likely to be lost, or damaged in the process, resulting in a loss of species richness. Displacement is unlikely to leave the reef intact. Therefore, an intolerance of intermediate has been recorded at the benchmark level. Although, individual pieces or fragments of the coral will probably survive, it would still take considerable time for a coral coppice or reef to develop.

Chemical Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information Not relevant No information Insufficient
information
Not relevant
No information was available concerning the effects of synthetic chemicals on Lophelia or other cold-water coral species. Evidence from a variety of sources suggests that hydroids, crustaceans, gastropods, and ascidians are probably intolerant of tri-butyl tin (TBT) contamination while bryozoans are probably intolerant of chemical pollution (see CR.Bug or MCR.Flu for details) (Smith, 1968; Hoare & Hiscock, 1974; Boero, 1984; Bryan & Gibbs, 1991; Gili & Hughes, 1995; Rees et al., 2001). It is likely that exposure to synthetic chemical contaminants may result in loss or degradation of populations of associated suspension feeding invertebrates, while there is no evidence to suggest either the presence or absence of adverse affects on Lophelia itself. Overall, in the absence of evidence of the effects of synthetic contaminants on the key structural species within the biotope (Lophelia), no assessment of intolerance has been made.
Heavy metal contamination
No information Not relevant No information Insufficient
information
Not relevant
Deep-water corals could potentially be exposed to heavy metal contamination as a result of spoil dumping or exposure to drill muds and drill cuttings. For example, barium sulphate from drilling muds has been found up to 6 km from an individual platform in the North Sea, covering an area of 100 km² (Olsgard & Gray, 1995; Rogers, 1999). Olsgard & Gray (1995) demonstrated four categories of contamination (from gross, severe, moderate to initial) radiating from oil rigs, which were mirrored by the benthic fauna. The effects were mainly due to total hydrocarbons, barium, strontium, and other metals such as zinc, copper, cadmium, and lead. The initial effects of pollution were the severe reduction of species that were key components of benthic communities (Olsgard & Gray, 1995).

Bryozoans may be tolerant to heavy metals while hydroids studied manifest only sublethal effects (Ryland, 1967; Soule & Soule, 1979; Stebbing, 1981; Bryan, 1984; Holt et al., 1995; Ringelband, 2001). Echinoderms may be intolerant of heavy metal contamination which has been shown to reduce reproduction and recruitment in starfish and sea urchins (see CR.Bug; Kinne, 1984; Dinnel et al., 1988; Besten, et al., 1989, 1991; Gomez & Miguez-Rodriguez 1999). Sea urchin larvae are used to test water quality and may be expected to be intolerant of. Gastropod molluscs have been reported to be relatively tolerant of heavy metals while a wide range of sublethal and lethal effects have been observed in larval and adult crustaceans (Bryan, 1984).

However, no information concerning the effects of heavy metal contamination on Lophelia or other cold-water corals was found. Roberts (2002a) noted that colonies of Lophelia growing on the Beryl Alpha platform in the North Sea were ca 2 km away from the site of drilling and its associated drill cuttings, although a single colony occurred 210 m upstream of the drill cuttings pile. It appears that heavy metal contamination from oil exploitation may reduce the abundance of marine invertebrates within its vicinity, and may adversely effect the species richness of a nearby reef. But the direct effects on the corals themselves remain unknown. Therefore, no assessment of intolerance has been made.
Hydrocarbon contamination
Low Very high Very Low Decline Low
Lophelia reefs are protected from the effects of oil spills by their depth but may encounter hydrocarbon contamination resulting from oil and gas exploitation. Corals were reported to exhibit a range of effects to oil contamination including mortality if contamination was severe, or reduced growth, tissue damage, disruption of cell structure, damage to feeding behaviour, and excessive mucus production in response to chronic contamination. Oil contamination was also reported to cause corals to release brooded planula larvae prematurely, and affect the settlement of larvae, decrease the coral's fecundity, and even result in reproductive failure (for reviews see Loya & Rinkevich, 1980; Rogers, 1999).

The effects of oil contamination of a numbers of species from numerous taxonomic groups has been studied. Overall, several species of bryozoans, amphipods, echinoderms and soft corals may be highly intolerant of hydrocarbon contamination, while some species of hydroid may demonstrate sublethal effects and anemones and some species of sponge are probably relatively tolerant (for examples see CR.Bug and MCR.Flu).

No information on the effects of hydrocarbon contamination on cold-water corals was found. However, the above evidence suggests that chronic contamination may result in sub-lethal effects and interfere with reproduction and hence recruitment in cold-water corals. Similarly, hydrocarbon contamination is likely to effect other members of the biotope adversely, reducing species richness and changing the composition of the community. Therefore, in the absence of further evidence an intolerance of intermediate has been recorded, albeit with low confidence.
Radionuclide contamination
No information Not relevant No information Insufficient
information
Not relevant
No information concerning the effects of radioactive contamination on Lophelia was found. However, Hall-Spencer et al. (2002) noted that although all shallow water organisms had accumulated nuclear bomb test related 14C, the Lophelia specimens collected from deep-waters off west Ireland were not contaminated by anthropogenic 14C, presumably because the water bodies they occupy are ancient. Therefore, Lophelia at sites in west Ireland could provide a useful background or baseline level for studies of radioactive contamination.
Changes in nutrient levels
No information Not relevant No information Insufficient
information
Not relevant
No information concerning the effects of nutrient levels on Lophelia and its associated community was found.
Not relevant Not relevant Not relevant Not relevant Not relevant
Lophelia pertusa occurs in waters of 35 -37 psu but in fjords tolerates salinities as low as 32 psu (Rogers, 1999; Mortensen et al., 2001). However, Rogers (1999) regarded Lophelia to be stenohaline. The Lophelia reef and its associated fauna occur in relatively stable waters, that are not subject to fluctuations in salinity. While Lophelia is probably highly intolerant of changes in salinity at the benchmark level, it is unlikely to experience an increase in salinity except is rare cases such as the unlikely production of hypersaline effluents by offshore installations. Therefore, not relevant has been recorded.
Intermediate Very low / none No information Minor decline Moderate
Lophelia pertusa occurs in waters of 35 -37 psu but in fjords tolerates salinities as low as 32 psu (Rogers, 1999; Mortensen et al., 2001). However, Rogers (1999) regarded Lophelia to be stenohaline. The Lophelia reef and its associated fauna occur in relatively stable waters, that are not subject to fluctuations in salinity. While Lophelia is probably highly intolerant of changes in salinity at the benchmark level, it is unlikely to experience an increase in salinity except is rare cases such as the unlikely production of hyposaline effluents by offshore installations. However, in shallow fjordic water Lophelia is restricted to the deeper, stable oceanic water below the relatively reduced salinity coastal waters at the surface. An increase in freshwater runoff, may increase the depth of the pycnocline and would probably result in death of the upper extent of the reef. Therefore, an intolerance of intermediate has been recorded. Recovery would probably take several hundred years (see additional information below).
No information Not relevant No information Not relevant Not relevant
It has been suggested that the lower limit of Lophelia's bathymetric distribution was probably determined by the oxygen minimum zone (Freiwald, 1998; Rogers, 1999) . However, Roberts et al. (2003) suggested the lower depth limit of Lophelia's distribution in the northeast Atlantic was related to temperature. Without information concerning the levels of hypoxia to which a Lophelia reef may be exposed, and its subsequent tolerance to hypoxia, no intolerance assessment has been made.

Biological Pressures

 IntoleranceRecoverabilitySensitivityRichnessEvidence/Confidence
No information Not relevant No information Insufficient
information
Not relevant
No information on diseases was found. However, the parasitic foraminiferan Hyrrokkin sarcophaga was reported growing on polyps of Lophelia pertusa in aquaria (Mortensen, 2001). The foraminiferan dissolves a hole in the coral skeleton and invades the polyp. In his aquaria, two Lophelia polyps became infested but did not seem to be influenced by the infestation (Mortensen, 2001). Any parasitic infestation is likely to reduce the viability of the host, even if only a few or possibly hundreds of polyps were affected but in the absence of additional evidence no assessment of intolerance has been made.
No information Not relevant No information Not relevant Not relevant
No alien or non-native species are known to compete with Lophelia pertusa or other cold-water corals.
High Very low / none Very High Major decline Low
Extraction of Lophelia pertusa colonies from the reef would result in fragmentation of part of the coral, and destruction of parts of the reef structure. Although not directly exploited, indirect removal of the coral as by-catch in bottom trawling has been shown result in damage to cold-water reefs (see physical disturbance above). Destruction of the cold-water reefs resulted in a marked reduction in the species richness of seamounts off Tasmania (Koslow et al., 2001). Reefs are considered to be good fishing places for net and long-line fisheries, and fishermen often set their gear as close as possible to reefs but not on them to avoid damaging their fishing gear. However, the development of larger vessels and more powerful trawls, e.g. rockhopper gear designed to operate on rough stony bottoms, has probably exposed the reefs to increased impacts from fishing (Fosså et al., 2002; Fosså, 2003). For example, the fishery of the continental break targeted Greenland halibut, redfish, and saithe. The orange-roughy is another valuable deep-sea species associated with offshore banks, pinnacles and canyons with strong currents, which are favoured by Lophelia (Rogers, 1999). In the UK, monkfish is a major fishery in the vicinity of the Lophelia reefs around Rockall (Dr Jason Hall-Spencer, pers comm.).

Overall, there is significant evidence of damage to Lophelia and other cold-water coral reefs due to deep-sea trawling, and an overall intolerance of high has been recorded. Recovery would probably take several hundreds to thousands of years (see additional information below).

High Very low / none Very High Major decline Low

Additional information

Recoverability
Fragmentation of the coral skeleton is part of the process of reef growth and development (Wilson, 1979b; Rogers, 1999). Therefore, minor damage to colonies is probably a natural process within reef formation. However, Lophelia pertusa exhibits extremely slow growth rates. For example, a single colony 1.5 m high may take between 200 -366 years to develop depending on growth rate. Large reefs may take several hundred to several thousand years to develop (see 'time for community to reach maturity') (Rogers, 1999).

If areas of the cold-water coral reef are removed, the area may be colonized by expansion from the remaining reef, or by recruitment by larvae. Although recent evidence suggests that Lophelia pertusa has a dispersive, pelagic larva (Roberts, 2002), the larval biology of Lophelia pertusa is completely unknown, and effective recruitment rates can not be predicted (Rogers, 1999). However, recent molecular genetic data suggests that larval recruitment is probably low or sporadic (Le Goff-Vitry & Rogers, 2002, summary only; Dr Alex Rogers, pers comm.). Even if recruitment is successful, it would still take considerable time for the new colony to grow, and even longer for a reef to recover. Rogers (1999) noted that if a cold-water coral reef was damaged by excessive sedimentation, then surface sediment would probably preclude larval settlement, preventing recovery.

Death of the coral polyps themselves would not immediately result in loss of the reef and the associated species. The associated species, especially epifauna would be lost over a period of years as the coral matrix was slowly eroded to coral rubble and eventually sediment. Although Lophelia may be able to colonize the substratum in the meantime, it would still take many years to replace the original reef.

Overall, any damage sustained by the cold-water coral reef may take at least decades but most probably hundreds of years to repair. The recovery of a destroyed large cold-water coral reef to its former size would probably take several hundred to several thousands of years.

Importance review

Policy/Legislation

Habitats of Principal ImportanceCold-water coral reefs [Scotland]
Habitats of Conservation ImportanceCold-water coral reef
Habitats Directive Annex 1Reefs, Reefs
UK Biodiversity Action Plan PriorityCold-water coral reefs
OSPAR Annex VLophelia pertusa reefs
Priority Marine Features (Scotland)Cold-water coral reefs

Exploitation

Lophelia reefs are not exploited directly but occur in areas subject to deep sea fishing (Rogers, 1999; Fosså et al., 2002; Hall-Spencer et al., 2002). The decline of traditional fisheries (e.g. cod) has resulted in increased interest in deep-sea species since the late 1980s (Rogers, 1999). Reefs are considered to be good fishing places for net and long-line fisheries, and fishermen often set their gear as close as possible to reefs but not on them to avoid damaging their fishing gear. However, the development of larger vessels and more powerful trawls, e.g. rockhopper gear designed to operate on rough stony bottoms, has probably exposed the reefs to increased impacts from fishing (Fosså et al., 2002). For example, the fishery of the continental break targeted Greenland halibut, redfish, and saithe. The orange-roughy is another valuable deep-sea species associated with offshore banks, pinnacles and canyons with strong currents, which are favoured by Lophelia (Rogers, 1999). In the UK, monkfish is a major fishery in the vicinity of the Lophelia reefs around Rockall (Dr Jason Hall-Spencer, pers comm.). Major fisheries in the vicinity of the 'Darwin Mounds' include deep-water demersal trawls for blue ling, orange roughy with a by-catch of black scabbard fish, Portuguese dogfish and leaf-scale gulper shark, long-lining for hake and deep-water sharks, and semi-pelagic trawling for blue whiting and argentine (Gubbay et al., 2002).

The potential effects of deep-sea fishing on the seabed and deep-water coral reefs has become a major concern (Rogers, 1999; Fosså et al., 2002; Hall-Spencer et al., 2002; Grehan et al., 2003). Photographic evidence of the effects of trawling damage, long line or fixed net fisheries, and discards on Lophelia reefs is shown in Fosså et al. (2002); Hall-Spencer et al., (2002) and Fosså (2003).

Additional information

Evidence of damage to their cold-water coral reefs prompted Norway to designate its most important Lophelia reefs as marine reserves recently and ban towed-gear fisheries from them (Johnston & Tasker, 2002). Similarly, both Australia and New Zealand have created a network of seamount protected areas (Grehan et al., 2003). Grehan et al. (2003) found no evidence of trawl related damage in five deep-water coral locations in the Irish Porcupine Seabight and the Rockall Trough and suggested that these sites should be subject to protection urgently, especially in the light of the expanding deep-water fishery for orange-roughy. The 'Darwin Mounds' in the Rockall Trough are probably the most intensively studied cold-water coral reef known in UK waters. The 'Darwin Mounds' have recently been proposed as the first offshore candidate Special Area of Conservation (Johnston & Tasker, 2002). An outline management plan for the 'Darwin Mounds' was proposed by Gubbay et al. (2002). Grehan et al. (2003) noted that deep-water corals: may provide spawning grounds and refugia for juvenile fish of commercial fish species;may be a major source or sink of carbonate;could potentially be a paleo-climate indicator for the study of global climate change;and may be a potential source of novel pharmaceutical compounds. In addition, Hall-Spencer et al. (2002) noted that although all shallow water organisms had accumulated nuclear bomb test related 14C, the Lophelia specimens collected from deep-waters off west Ireland were not contaminated by anthropogenic 14C, presumably because the water bodies they occupy are ancient. Therefore, Lophelia at sites in west Ireland could provide a useful background or baseline level for studies of radioactive contamination.

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Citation

This review can be cited as:

Tyler-Walters, H., 2005. Lophelia reefs. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/habitat/detail/294

Last Updated: 04/07/2005