Abstract
Seamounts are unique deep-sea features that create habitats thought to have high levels of endemic fauna, productive fisheries and benthic communities vulnerable to anthropogenic impacts. Many seamounts are isolated features, occurring in the high seas, where access is limited and thus biological data scarce. There are numerous seamounts within the Drake Passage (Southern Ocean), yet high winds, frequent storms and strong currents make seafloor sampling particularly difficult. As a result, few attempts to collect biological data have been made, leading to a paucity of information on benthic habitats or fauna in this area, particularly those on primarily hard-bottom seamounts and ridges. During a research cruise in 2008 six locations were examined (two on the Antarctic margin, one on the Shackleton Fracture Zone, and three on seamounts within the Drake Passage), using a towed camera with onboard instruments to measure conductivity, temperature, depth and turbidity. Dominant fauna and bottom type were categorized from 200 randomized photos from each location. Cold-water corals were present in high numbers in habitats both on the Antarctic margin and on the current swept seamounts of the Drake Passage, though the diversity of orders varied. Though the Scleractinia (hard corals) were abundant on the sedimented margin, they were poorly represented in the primarily hard-bottom areas of the central Drake Passage. The two seamount sites and the Shackleton Fracture Zone showed high numbers of stylasterid (lace) and alcyonacean (soft) corals, as well as large numbers of sponges. Though data are preliminary, the geological and environmental variability (particularly in temperature) between sample sites may be influencing cold-water coral biogeography in this region. Each area observed also showed little similarity in faunal diversity with other sites examined for this study within all phyla counted. This manuscript highlights how little is understood of these isolated features, particularly in Polar regions.
Highlights
Since the opening of the Drake Passage, some 30 million years ago [1,2,3] the Antarctic Circumpolar Current (ACC) is thought to create a biogeographical barrier to species dispersal, limiting the transport of benthic larvae between the South American and Antarctic continental shelves
Towed camera surveys were conducted at six locations (Fig. 1, Table 1) – the continental margin off Elephant Island at 450 m (EL-1) and at 1900 m (EL-2); along the Shackleton Fracture Zone at 800 m(SFZ); Interim Seamount at 1175 m (INT-1) and 1500 m (INT-2); and Sars Seamount at 610 m (SARS)
Though other studies have suggested that seamount communities are most closely affiliated with those on the nearest continental margin [13] this study, even at phylum level, shows a distinct difference in faunal makeup between the Western Antarctic Peninsula (WAP) continental margin sites and sites within the Drake Passage
Summary
Since the opening of the Drake Passage, some 30 million years ago [1,2,3] the Antarctic Circumpolar Current (ACC) is thought to create a biogeographical barrier to species dispersal, limiting the transport of benthic larvae between the South American and Antarctic continental shelves. The Drake Passage in particular is a highly dynamic environment, where fast currents are likely to hinder meridional larval transport [4]. Antarctic benthic fauna have been thought to be ‘‘cut off’’ from South American fauna since this time, and have a long history of in situ evolution on the deep continental shelf [5,6]. Despite this separation, faunal similarities have been found in both fossil and live benthic groups bringing into question these theories of larval isolation [5,7]. Though the majority of the passage lies in abyssal depths of over 3000 m, there are numerous ridges and seamounts
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