Preliminary assessment of Benthic Infauna at Cape Three Points in the Western Region of Ghana

Abstract

Many  of  the  potential  impacts  of  oil  and  gas  exploration  and  production  activities  in benthic  environments   are   well-known  in  shallow  waters  but  relatively  little-known  in deep  water  environments.  Ghanaian commercial oil discovery in June 2007 is located at depths of 1,100 m and 1,700 m within the Jubilee Oil and Gas Field between the Deep water Tano and West Cape Three Points blocks. The data for the study was collected in May, 2009 to obtain baseline information on the benthic ecology of the Jubilee Field and its environs for future impact assessments. In order to ascertain gradients in biological variables, sediment samples were collected along defined depths between 25 m and 1200 m along three transects. Abundance and biomass of major infaunal groups were assessed. Univariate  techniques  using  distributional  trends of  diversity indices  and  multivariate  techniques  such  as  agglomerative  cluster  analysis and  Non-metric Multidimensional  Scaling  (MDS) were employed in the analyses of the data.  A total of 265 individuals (average density = 176 ind. /m²) comprising 77 species belonging to four major taxonomic groups were recorded. Polychaetes  constituted 72%  of the  abundance  followed  by  crustaceans  (14%), echinoderms  (6%) and  others (eg. cnidarians,  sipunculids, etc.) (8%). No species of the phylum Mollusca were recorded. The spatial  distribution  and  occurrence  of  species showed  sipunculids appearing  in  47%  of  the  sampled  stations,  making  them the  most commonly   distributed   in   the   area. The echinoderm Ophiotrix   sp., and   polychaete Magelona cincta occurred in 40%  of locations.  Fifty-four percent of the species were recorded in only one or two samples.  Species diversity and richness revealed a general declension from the west to the east of the Jubilee oil rig. The findings indicated a decreasing trend of species diversity from 500 m and beyond, suggesting that future disturbances may not have any effect on the benthic fauna. It may just affect the distribution of a few rare species in the deep water areas.