Spatial and temporal patterns of benthic macrofaunal communities on the deep continental margin in the Gulf of Guinea

• Published in: Deep-sea research. Part II, Topical studies in oceanography Topical studies in oceanography, 2009-11, Vol.56 (23), p.2299-2312
• Main Authors: Galéron, J., Menot, L., Renaud, N., Crassous, P., Khripounoff, A., Treignier, C., Sibuet, M.
• Format: Article
• Language: English
• Subjects: Atlantic; Channels; Communities; Community structure; Congo canyon; Congo–Angola margin; Deep sea; Density; Distribution; Equatorial west Africa margin; Foods; Gulfs; Isopoda; Macrofauna; Marine; Sciences of the Universe; Sediments; Submarines; Vertical distribution
• ISSN: 0967-0645; 1879-0100
• DOI: 10.1016/j.dsr2.2009.04.011

Density, taxonomic composition at higher taxon level and vertical distribution of benthic macrofaunal communities and sediment characteristics (pore water, nitrogen, organic carbon, sulfur, C/N ratio, n-alcohol biomarkers) were examined at three deep sites on the Congo–Gabon continental margin. This study was part of the multidisciplinary BIOZAIRE project that aimed at studying the deep benthic ecosystems in the Gulf of Guinea. Sampling of macrofaunal communities and of sediment was conducted during three cruises (January 2001, December 2001 and December 2003) at two downslope sites (4000 m depth), one located near the Congo submarine channel (15 km in the south) and the other one far from the channel (150 km in the South). The third area located 8 km north of the Congo channel in the surroundings of a giant pockmark at 3160 m depth was sampled during one cruise in December 2003. At these three locations the macrofaunal communities presented relatively high densities (327–987 ind. 0.25 m −2) compared with macrofaunal communities at similar depths; that is due to high levels of food input related to the Congo river and submarine system activities that affect the whole study area. The communities were different from each other in terms of taxonomic composition at higher taxon level (phylum, class, order for all the groups except for the polychaetes classified into families). The polychaetes dominated the communities and were responsible for the increase in densities observed at both deep sites (4000 m) between January 2001 and December 2003 whereas the tanaidaceans, the isopods and the bivalves were the other most abundant taxa responsible for the spatial differences between these sites. The community at 3150 m differed from the two deep communities by higher abundances in bivalves, nemerteans and holothuroids. The composition of the polychaete community also differed among sites. In the vicinity of the Congo channel, the expected positive effect of the additional organic matter transported through the turbiditic currents on to the surrounding benthic communities was not observed, as the increase in densities during the study period was higher at the site located away from the Congo channel than near the channel (80% vs 30%). That may be due to the low food value of the organic matter of terrestrial origin carried through the turbidites, and/or to the disturbance caused by these turbidites. Conversely, far from the channel the macrofaunal communities benefit