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Patterns in species diversity of polar megabenthos assemblages: Comparative case studies in the eastern Weddell Sea (Antarctica) and northwestern Greenland Sea (Arctic)

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Piepenburg, D. and Gutt, J. (2003): Patterns in species diversity of polar megabenthos assemblages: Comparative case studies in the eastern Weddell Sea (Antarctica) and northwestern Greenland Sea (Arctic) , GFÖ-Symposium 2003. .
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Abstract:

There is a broad agreement among marine ecologists that general comparisons of diver-sity and abundance of Arctic and Antarctic seas can easily lead to ambiguous conclu-sions, as such analyses often synoptically summarise the results of different investiga-tions and are, hence, heavily affected by discrepancies in methodology and spatial scale. Here, we report the findings of case studies on the composition and distribution of megabenthos assemblages in the Weddell Sea (Antarctica) and in the waters off North-east Greenland (Arctic). These investigations were truly comparative because they were based on quantitative surveys using the same sampling approach?a combination of sea-bed imaging and Agassiz trawling?and standardized sampling protocols.Multivariate analyses of species abundance data revealed a conspicuous depth zonation of the megabenthos fauna off Greenland where dense brittle star beds with abundances of several hundreds individuals m-2 characterized the benthos of shallow shelf banks (< 140 m). Such high megabenthic densities were not discovered in the Weddell Sea where deep shelf trenches (> 600 m) and the actual shelves (140 to 550 m) housed distinct assemblages.Special emphasis was on an inventory of the asteroid (sea star) and ophiuroid (brittle star) fauna. Diversity patterns were analysed at various spatial scales. At a large scale (epsilon diversity), the Antarctic seas housed conspicuously more species than the waters off Greenland. Species numbers totalled 86 (48 sea stars and 38 brittle stars) in the Weddell Sea, whereas off Northeast Greenland a total of only 26 species (16 sea stars and 10 brittle stars) were recorded. This finding corroborates the conclusions of previous comparisons between Arctic and Antarctic regions. At both regional and local scales (gamma and alpha diversity, respectively), higher species diversity was also evi-dent for the rich eastern Weddell Sea shelf but not for the other, markedly poorer Ant-arctic areas. Moreover, because many species from the Weddell Sea are phylogenetically closely related, the Antarctic assemblages were not significantly different from the Arctic ones in terms of taxonomic diversity and distinctness.These findings indicate that different processes determine the diversity patterns in the polar areas investigated. Furthermore, we conclude that the often-cited paradigm of a pronounced Arctic-Antarctic diversity difference is a gross over-generalization and does not apply in equal measure to all spatial scales and each aspect of biodiversity.

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