|Gemeenschapsanalyse van macrofauna geassocieerd met koudwaterkoraalriffen in de NO Atlantische Oceaan|
Van Gaever, S. (2001). Gemeenschapsanalyse van macrofauna geassocieerd met koudwaterkoraalriffen in de NO Atlantische Oceaan. MSc Thesis. Universiteit Gent (RUG): Gent. 110 pp.
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Deep-water corals are widespread ecosystems that occur at many locations throughout the world. These corals have a bathymetric distribution from 0 m to a depth of 6200 m, they also occur in the dark, cold, upper bathyal zone of the ocean. Although these deep-water corals were first recorded in the 18th century, they only have received much attention during the last ten years. These unique ecosystems are threatened by the increasing human exploration of the natural sources of the continental slopes. Lophelia pertusa (Linnaeus 1758) is a reefbuilding and very common deep-water coral. Scientists presume even that the associated fauna of Lophelia would be as divers as the fauna occurring in the tropical coral reefs. The purpose of this thesis is to make an analysis of the associated community of Lophelia pertusa in the North-East Atlantic. In this area occur several clusters of carbonate mounds, (Henriet et al. 1998). The deep-water corals are situated on the flanks and the summits of these mounds. The samples analysized in this study were taken in three different areas of the NE Atlantic southwest of Ireland: the Porcupine Seabight, the Porcupine Bank and the Rockall Bank. Rogers (1999) presented a list of 886 species that were found on or in a Lophelia pertusa reef. Further studies of Mortensen et al. (1995) and De Bergé (1999) also made supplementary lists. Of the 142 different species found in this study, there were 58 species that were not mentioned in these lists. These organisms are in this study probably for the first time found in association with Lophelia. The reef community of Lophelia will be much more divers than known so far, and further research is necessary. Just like in previous studies the Polychaeta are the most dominant group with the highest number of species and individuals (Jensen & Frederiksen 1992 ; De Bergé 1999). Also the Crustacea, Nematoda and Ophiuroidea are very abundant groups in the samples analysed in this study. From the ecology of the most abundant species appeared that many of these species have a large bathymetric distributions and that they are often widespread organisms. The idea of Dons (1944) that the associated fauna of Lophelia pertusa is a unique community, is difficult to accept. Also later studies are of the opinion that these fauna is not typical for this habitat (Burdon-Jones & Tambs-Lyche 1960; Jensen & Frederiksen 1992). The associated fauna will probably consist of species that have developed a specific adaptation to the coral reef but that also occur elsewhere, and species that are casual immigrants from the nearby habitats. The comparison of the samples with sediment showed that the endofaunas from the Porcupine Seabight and from the Porcupine Bank have many different species, but that they have a similar composition on an higher taxonomic level. It was obvious that the sediment from the samples without coral or sponge had a very poor fauna. The area between the mounds and where no Lophelia reef occur had a much less divers fauna than the Lophelia reefs. The comparison of the two nearby mounds in the Porcupine Seabight showed that even on a small scale there is a high variety of associated species. In the samples analysed in this study, the microhabitat sediment was the most biodivers microhabitat, followed by the dead coral skeleton. In general this Lophelia skeleton is in the different regions the microhabitat with the highest diversity index (Mortensen et al. 1995 ; Jensen & Frederiksen 1992). Some groups of the fauna are mainly associated with a certain microhabitat: the nematodes (> 1 mm) are especially found in the sediment, while the bivalves and the brittle stars are clearly more abundant on the dead coral. From the literature study it appeared that the Lophelia reefs in the Porcupine Seabight have a slightly less biodiversity than the Lophelia reefs and other deep-water coral reefs in o