Abstract
Infaunal communities of benthic macro-organisms (≥ 1mm length) were studied from 81 samples collected across nine sites to the north and south of the Orange River in the Benguela upwelling ecosystem in 2003, with a view to describing communities and understanding the drivers of regional community structure, as well as to document diversity and to examine geographic affinities. Although the fauna was dominated by polychaetes and peracarid crustaceans, patterns in community structure could only weakly be explained by the measured environment (~35%). This is attributed to the generalist nature of the species recovered, which were widely distributed amongst different sediments, water-depths and latitudes. The fauna is dominated by species that enjoy a widespread regional and global distribution and is characterised by relatively low diversity, which is discussed.
Highlights
Coastal-upwelling ecosystems are amongst the most productive in the world, where pelagic systems are characterised by short diatom-based food chains leading to industrial scale fisheries [1]
The study area is located over the inner shelf north and south of the Orange River, the latter marking the political boundary between Namibia and South Africa (Fig 1)
Sediments at most sites were dominated by sand, those collected at the two sites immediately north (MLA1 South) and south (ML3 North) of the Orange River contained large amounts of mud (Table 1)
Summary
Coastal-upwelling ecosystems are amongst the most productive in the world, where pelagic systems are characterised by short diatom-based food chains leading to industrial scale fisheries [1]. Diversity is correspondingly low, perhaps because the high levels of environmental instability prevents the fine-tuning of genotypes to local conditions [2] This favours habitat generalists (as at polar latitudes [3]), few of the dominant species are shared amongst the four (Benguela, Humboldt, Canary and California) major upwelling systems [2]: and those that are tend to be large and migratory. The benthic habitat of these upwelling ecosystems is often characterised by large areas of diatomaceous ooze, fed by the sedimentation of excess surface production [4] This environment is associated with low concentrations of dissolved oxygen (
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