Abstract
Abundance, biomass and diversity patterns of bathyal and abyssal Mediterranean megafauna (fishes and invertebrates) were analyzed in the western Balearic Sea, the western Ionian Sea and the eastern Ionian Sea. Sampling was conducted with a Otter-trawl Maireta System (OTMS) at depths ranging from 600 to 4000 m. A series of ecological indicators were computed: total abundance and biomass, Margalef species richness, Shannon-Wiener diversity and Pielou’s index of evenness. A multidimensional scaling was applied, indicating that the megafauna communities were grouped by depth, while geographic area had a less defined influence. Margalef richness declined with depth in all three areas, but more steeply in the western Ionian Sea. Pielou’s evenness behaved differently in the three zones, showing a V-shaped curve in the eastern Ionian while showing a decreasing pattern in the other two areas. At lower slope depths, massive presence of the fishes Alepocephalus rostratus in the western basin and Bathypterois mediterraneus in the central basin caused a sharp reduction in evenness.
Highlights
Deep-sea ecosystems are known to be the largest repository of biodiversity of the biosphere (Sanders, 1968; Gage and Tyler, 1991), but remain mostly unknown because of extreme conditions in sampling techniques
A multidimensional scaling was applied, indicating that the megafauna communities were grouped by depth, while geographic area had a less defined influence
Margalef richness declined with depth in all three areas, but more steeply in the western Ionian Sea
Summary
Deep-sea ecosystems are known to be the largest repository of biodiversity of the biosphere (Sanders, 1968; Gage and Tyler, 1991), but remain mostly unknown because of extreme conditions in sampling techniques. New insights into deep-sea biodiversity are necessary in order to better understand the grade of stability and vulnerability of these environments (Merrett and Haedrich, 1997), but should focus on largescale analyses (Bianchi and Morri, 2000) dealing, for example, with a whole enclosed deep-sea environment. The Mediterranean Sea is an optimal environment for studying the patterns of biodiversity for several reasons. First of all, it is an enclosed sea with limited connection with the outer Atlantic ocean.
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