BRITISH COLUMBIAN CORALS (2009)
Fisheries and Oceans Canada | Pacific Biological Station, Nanaimo, BC V9T 6N7
Pêches et Océans Canada | Pacific Biological Station, Nanaimo, BC V9T 6N7
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Cold-water corals occur throughout the world’s oceans, from the Antarctic to the Arctic and within the Mediterranean Sea. Typically, these corals are found in relatively shallow continental shelf and slope waters (Roberts et al., 2006), 50-1000 m depth, including shelf-edge canyons, deep channels between fishing banks (MacIsaac et al., 2001) and on fjord walls. However, cold-water corals, mostly gorgonians and hydrocorals, in the eastern North Pacific are most abundant in a much narrower depth zone. The most extensive coral surveys in the eastern North Pacific have been conducted in the Aleutian Islands. Limited submersible data to 367 m there found that corals were most abundant between 100-200 m, with mean coral abundance (3.85 colonies m-2 over 25 transects) far exceeding that reported for other high-latitude ecosystems (Stone, 2006).
We use the term ‘coral’ for members of the class Anthozoa, subclasses Octocorallia (soft corals, black corals and sea fans) and Hexacorallia (stony and cup corals); and class Hydrozoa, order Filifera (fire and lace corals). Although we include the octocoral orders Alcyonacea, Antipatharia and Penntulacea as corals, only the hexacoral order Scleractinia is included, because other hexacoral orders (e.g., Actiniaria, Zoanthidea) are not skeletonized. Our octocoral classification follows Williams and Cairns (last revised January 2006), which uses a system of higher taxa after Bayer (1981) for Helioporacea and Alcyonacea, and Kükenthal (1915) and Williams (1995) for Pennatulacea. Because it is quite recent, this classification does not always agree with current Integrated Taxonomic Information System (ITIS) data on the web; e.g., species in the order Gorgonacea have been included in the order Alcyonacea by Williams and Cairns (2006), though the order is still shown as separate in ITIS. Octocorals, scleractinians and hydrozoan corals can be either zooxanthellate or azooxanthellate, while antipatharians are strictly azooxanthellate. Cold-water corals that exist below the photic zone do not form symbiotic associations and are thus azooxanthellate.
The majority of cold-water corals are solitary as well as azooxanthellate. However, a few colonial forms are hermatypic, e.g., Lophelia pertusa and Dendrophyllia sp., that is, their skeletons accumulate as biogenic build-ups. Deep- and cold-water coral accumulations have been called reefs, banks, mounds and bioherms. The term reef, while widely used, traditionally implied a navigational hazard. Tropical coral reefs are biogenic structures built by both reef-building scleractinians and coralline algae, each having a key “cementing” function in reef development. In contrast, cold-, and usually deep-water scleractinian reefs (e.g., Lophelia reefs) are built mainly by the corals themselves without any input from algae. However, shallow cold-water coral reefs have been poorly studied, so this generalization may not be true for all cold-water corals. Bioherm is a more general term for any biogenic build-up of skeletal remains on the site where the organisms lived. They may consist of coral, sponge or other skeletonised invertebrate fragments that have been built on and added to by successive generations. There is a distinction between true scleractinian coral reefs and octocoral ‘forests’, i.e., concentrations of octocorals, which seem to be more common in British Columbian waters than are true scleractinian reefs.
Cold-water corals can form an extensive structural habitat, but their spatial occurrence, biology and ecological significance are relatively poorly known due to their predominance in deep waters. However, Roberts at al. (2006) suggest that cold-water corals are arguably the most three-dimensionally complex habitats in the deep ocean, noting that over 1300 species have been found living on Lophelia pertusa reefs in the NE Atlantic. While their role in the marine benthic ecosystem has yet to be fully defined, cold-water corals are often found in association with numerous other species (Cimberg et al., 1981; Koslow et al., 2001; Witherell and Coon, 2001; Etnoyer and Morgan, 2003; Gass, 2003; Hyland et al., 2004; and Stone, 2006), leading to the precautionary concern that coral concentrations in particular may have an important ecosystem role and thus should be particularly conserved.
Cold-water coral structures range from small, solitary individuals to massive reef habitats, often in relatively barren surroundings. Habitat-forming cold-water corals include octocorals, hexacorals (hermatypic scleractinian corals) and hydrocorals (Roberts et al., 2006). Live and dead portions of a coral’s matrix or lattice framework can create substratum and shelter for other corals, sponges, brachiopods, bivalves, crustaceans, bryozoans, crinoids and tunicates (Hall-Spencer et al., 2001; Koslow et al., 2001). The complex branching morphology of many cold-water corals creates structures of sufficient size to provide substrate or refuge for other species (Etnoyer and Morgan, 2003; Stone, 2006; Roberts et al., 2006).
The majority of cold-water corals exhibit preference for rocky substrate or hard surfaces with moderate to strong currents, although pennatulaceans (species in the order Pennatulaceae) generally prefer unconsolidated substrates. Preferred coral substrate thus ranges from fine, well-sorted sand, gravel areas and shell deposits, to slump deposits with rock outcrops, boulders, crevices, rock pinnacles, over hangs, living habitat, sheer cliffs, and iceberg furrows (MacIsaac et al., 2001).
In Canada, cold-water corals have been reported from both Atlantic (Breeze et al., 1997) and Pacific waters (McAllister and Alfonso, 2001; Lamb and Handby, 2005). In Nova Scotia, distributions are limited by both geography and bathymetry (the study of lake or ocean floors) (Breeze and Davis 1998). Gass (2003) reported that the northeastern Pacific coral fauna was dominated by large gorgonian octocorals. In the Northeast Pacific, the most extensive regional surveys have been conducted in Alaskan waters (Heifetz, 2002; Etnoyer and Morgan, 2003; Stone, 2006).
Increased awareness of concentrations of cold-water corals and their high vulnerability to damage from human activities such as benthic fishing gear, coupled with new legislation (e.g., Canada’s Oceans Act) requiring ecosystem-based approaches to management, are providing a new impetus for describing coral occurrence and distribution off British Columbia. Better conservation of biogenic marine habitats is high on the agenda of environmental non-governmental organisations (e.g., Ardron, 2005), including the minimisation of impacts from fishing gear on benthic habitats (MacIssac et al., 2001).
Little published data exists on cold-water corals in British Columbia, with the papers by Jamieson et al. (2007) and Ardron et al. (2007) providing the most recent data on species lists and mapped coral occurrences from bycatch analyses of groundfish trawl data, respectively. Conway et al. (2005) reported BC corals from their ROV surveys in the 100-300 m depth range. However, with new discoveries (Cairns, 2007b), new taxonomic information (France, 2007) and validation of voucher specimens associated with each species, results in even the most recent versions are having to be updated.
Seamounts, i.e., extinct underwater volcanoes rising over 1,000 m from the seafloor, provide opportunity for patchy, wide-scale occurrence of benthic species in a primarily homogeneous environment. Canada’s Pacific Bowie Seamount has been recently surveyed, with research efforts targeted on a limited number of species (primarily rockfish and sablefish), but alcyonacean and scleractinian corals were observed there (Canessa et al., 2003). In 2002, seven seamounts (Patton, Murray, Chirikof, Marchand, Campbell, Scott and Warwick) from the Cobb Hotspot in the Gulf of Alaska were explored using submersibles and multibeam bathymetric surveys (Etnoyer and Morgan, 2003).
Conway et al. (2007) documented the remains of a large dead coral reef in the Strait of Georgia at 255 m, identified as Lophelia pertusa (S. Cairns, Smithsonian National Museum of Natural History, Washington, DC, pers. comm. to K. Conway) (Jamieson et al., 2006). While this particular reef did not contain live corals, its presence in British Columbian waters strongly suggests that other as-of-yet undiscovered Lophelia reefs likely exist in British Columbian waters. Austin (1985) reported this species, initially misidentified as Solenosmilia variabilis, from Alberni Inlet, Vancouver Island. Rogers (1999) and Hyland et al. (2004) listed other Lophelia records for the North Pacific, including Cobb Seamount and the American side of Juan de Fuca Canyon, but there are no other records from Canadian waters.n, W.G. and D.G. Fenton, eds.1. The Gully: A Scientific Review of its Environment and Ecosystem. CSAS Res. Doc. 1998/83.at Protection, Washington D.C. 32 p.
Read about coral bleaching and threats to corals
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