Deep-sea coral distribution on seamounts, oceanic islands, and continental slopes in the Northeast Atlantic

A database of deep-water (> 200 m) antipatharians, scleractinians, and gorgonians has been assembled for the NE Atlantic to determine what their distribution and diversity was before coral habitats became heavily impacted by bottom fishing gear. Benthic sampling expeditions from 1868–1985 have provided 2547 records showing the deepwater distribution of 22 species of antipatharians, 68 species of scleractinians, and 83 species of gorgonians with the majority of records found from seamounts, oceanic islands, and the continental slope of the warm temperate region. Too little is known about the coral biota of boreal and tropical seamounts to assess their levels of endemism, but on seamounts in the warm temperate region of the NE Atlantic the level endemism in antipatharian, scleractinian and gorgonian corals is low (< 3%). Many of the species found on seamounts are characteristic of oceanic islands in this region and the oceanic islands have a significantly different coral fauna to that recorded at the same depths on the continental slope. Given the key role that corals can play in structuring deep-sea habitats it is hoped that our database will help inform the development of a network of marine protected areas to provide long-term protection for the differing communities found on continental slopes and isolated offshore habitats. A surge of international research into seamount ecology (Malakoff, 2003; Pitcher et al., 2007) was recently boosted by work on South Pacific seamounts reporting that > 30% of the species found were new to science and potentially endemic to seamounts (Parin et al., 1997; Richer de Forges et al., 2000). Surveys to date show that deep-water coral communities often characterize seamount habitats and that these communities have been heavily impacted by trawling (Koslow et al., 2001; Rogers et al., 2007). The North Atlantic has the longest and most intensive history of biogeographic research, yet even there most seamounts remain unsampled (Stocks et al., 2004) and coral reefs several km in extent have only recently been discovered (Fosså et al., 2005). At the same time as these amazing discoveries are being made, benthic surveys are revealing the increasing extent to which bottom-trawling is altering the habitats of deep-sea corals worldwide (Hall-Spencer et al., 2002; Clark and O’Driscol, 2003). This is of particular concern considering that deep-water corals are amongst the longest lived and slowest growing organisms on Earth (Roark et al., 2006). In most parts of the world offshore expansion of the bottom-trawling industry began before any habitat assessment had taken place (Gordon, 2003). Fortunately, there is a wealth of historical deep-water coral data for the NE Atlantic providing detailed records dating back to the expeditions of the vessels Lightening, Porcupine, and Josephine (1868–1869). Regular sampling expediHALL-SPENCER, ROGERS, DAVIES, AND FOGGO 136 tions such as those funded by Prince Albert I of Monaco from 1886–1915 provide a rich source of information on the coral fauna (e.g., Studer, 1901; Thomson, 1927). Deep-water bottom-trawling was pioneered in the North Atlantic by the Russians in the 1970s targeting Coryphaenoides rupestris Gunnerus, 1765 (roundnose grenadier) south of Iceland and on the Reykjanes Ridge, but it was not until the late 1980s that deepwater bottom-trawling began to increase rapidly along the European continental slope with the development of new markets for Molva dypterygia (Pennant, 1784) (blue ling), Aphanopus carbo Lowe, 1839 (black scabbardfish), and Hoplostethus atlanticus Collett, 1889 (orange roughy) (Gordon, 2001, 2003). Deep-water trawling is now common, with trawl tracks clearly visible on acoustic images and seabed photographs of the European continental slope (Hall-Spencer et al., 2002). Damage continues partly because coralrich areas are poorly mapped, so trawlers do not know the key sites to avoid, and partly because only very small areas are closed to bottom-trawling (Butler, 2005; Wheeler et al., 2005). We aim to build on the approach adopted by Cairns and Chapman (2001) and Watling and Auster (2005), drawing attention to valuable baseline information on the diversity and distribution of deep-water scleractinian, gorgonian and antipatharian corals before bottom-trawling became widespread. We have collated a “pre-1985” database of deepwater corals of the NE Atlantic and use it to compare coral faunas on seamounts, continental slopes, and oceanic islands of the warm temperate region.