Angola Biodiversity of Bathyal Sea Bottoms

Abstract

At the request of TOTAL E&P Angola (TEPA), before developing oil and gas activity, independent contractors carried out seven environmental baseline studies between 1998 and 2009 on bathyal blocks 17 and 32 located off the coast of Angola. With this aim, biological analysis were done on seabed samples at depths ranging between 682 and 2630 m, and 515 benthic macrofaunal taxa from eleven phyla were discovered. The relative dominance on richness taxonomic and abundance was observed on Polychaetes, but referring to species' abundance it was found the sipunculid Onchnesoma steenstrupi (78 ± 72 ind./m²) with the major representation in samples (94%). The general composition of benthic macrofauna communities was very similar between sites despite the wide range of depths. This suggested relatively high ecosystem homogeneity in space and time. Average taxon richness per station (41 ± 11) was relatively high and the Shannon-Weiner diversity index very high (4.5 ± 0.5). Total density was relatively low (409 ± 179 ind./m²), as well as dry weight total biomass (0.57 ± 1.27 g/m²). Such levels of structural indices were consistent with common deep-sea soft sediment records. Increasing biodiversity from deep offshore Block 17 sites to ultra-deep offshore Block 32 area also was concordant with previous deep Angola Basin observations. When performing the taxonomic identification of species encountered in this work, it was estimated that about 80% of species found in both blocks were new to science. In respect of trophic structure of the groups, it was found that there was dominance of detritus deposits in relation to suspension feeders. Finally, it was also concluded that the state of the environment was stable, the ecosystem was in equilibrium and there was a high level of biodiversity.

Short-Term Response of Deep-Water Benthic Megafauna to Installation of a Pipeline Over a Depth Gradient on the Angolan Slope

“…Depth-related patterns in the fauna of the Angolan margin appear to be typical, as in other areas (Carney, 2005), potentially related to transition zones between overlapping faunal components. The sediment-dwelling macrofauna in Angola show a similar mid-bathyal peak in abundance and species diversity (Cazes et al, 2012) to that found here. There was also high turnover with depth reported in the Angolan fishes, for example in Rajidae (Compagno and Ebert, 2009) and virtually no overlap (only the hagfish Myxine ios) in fishes collected at shallower below 800 m (277 species) (Tweddle and Anderson, 2008) compared to deeper (1297-2453 m) areas (Jamieson et al, 2017).…”

“…These studies have mostly focussed on chemosynthetic systems in the deep bathyal (Sibuet and Olu-LeRoy, 2002;Sibuet and Vangriesheim, 2009) and abyssal (Sen et al, 2017) or deepwater coral reefs on the upper slope (Le Guilloux et al, 2009). Less scientific attention has been directed towards the bathyal (200 -2000 m) depths of the margin, although this area has been the subject of many environmental assessments by the oil industry (Cazes et al, 2012). Access to the region through oil company activities has permitted some scientific investigations on the scavenging fishes in Block 18 and 31 (Jamieson et al, 2017) and on communities associated with asphalt mounds in Block 31 (Jones et al, 2014).…”