Abstract
Three deep-sea areas in the Mediterranean Sea were sampled using a bottom otter trawl during the DESEAS oceanographic survey carried out from early June to early July 2001, covering an area in the western Mediterranean from 600 to 2800 m in depth and two areas in the central Mediterranean, the western and eastern Ionian Sea from 600 to 4000 m in depth. Decapod crustaceans were one of the dominant megafaunal groups, together with fishes, in terms of both biomass and abundance. A total of 2799 decapod specimens belonging to 32 species were collected. Abundance and biomass of the decapod crustaceans decreased with depth. For depths below 1000 m, a decrease in total decapod biomass was recorded from west to east. From the data reported in this study and data from the available literature, decapod crustaceans display differential depth distributions in the different areas. For the most abundant species, size and sex distributions versus depth gradient were examined to compare intraspecific population structures between the sampling areas. Despite differences, among areas, in the species biomass compositions by depth strata and differences in their overall bathymetric ranges of distribution, intraspecific population structures of the most abundant species seem to follow similar trends for size and sex distribution versus depth gradient between the western and central areas. This might be an indication that the individual species structure their populations according to a similar basic pattern regardless of differences in local environmental features. The results have been discussed in the general context of the environmental features encountered by the species in each of the sampling areas.
Highlights
Decapod crustaceans are one of the dominant megafaunal groups in the deep-sea communities of the Mediterranean Sea (Abelló et al, 1988; Cartes and Sardà, 1992; Sardà et al, 1994)
The relatively oligotrophic nature of Mediterranean waters has been presented as one of the environmental factors contributing to the high abundance of decapod crustaceans in comparison with other oceans, in which other megafaunal invertebrates, echinoderms, predominate (Tyler and Zibrowius, 1992; Sardà et al, 1994)
Community assemblages and boundaries as well as depth ranges of deep-sea species dwelling along the continental margins have been described in several regional seas of the Mediterranean (Abelló and Valladares, 1988; Cartes and Sardà, 1993; Pipitone and Tumbiolo, 1993; Ungaro et al, 1999; Kallianiotis et al, 2000), but no comparative work dealing with species composition and community structures in the Mediterranean basin as a whole is available
Summary
Decapod crustaceans are one of the dominant megafaunal groups in the deep-sea communities of the Mediterranean Sea (Abelló et al, 1988; Cartes and Sardà, 1992; Sardà et al, 1994). Community assemblages and boundaries as well as depth ranges of deep-sea species dwelling along the continental margins have been described in several regional seas of the Mediterranean (Abelló and Valladares, 1988; Cartes and Sardà, 1993; Pipitone and Tumbiolo, 1993; Ungaro et al, 1999; Kallianiotis et al, 2000), but no comparative work dealing with species composition and community structures in the Mediterranean basin as a whole is available. To the authors’ knowledge, the only comparative studies dealing with the biomass distribution and population characteristics of commercial demersal resources have recently been carried out down to 800 m depth within the framework of the MEDITS international
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