Abstract |
For the description of the deep water benthic ecosystem of Crete, macrofauna
samples were collected along a bathymetric gradient in the oligotrophic system of Eastern
Mediterranean. Samples were collected from 17 stations, which were located along 5
transects at depths from 215 m to 3600 m.
The samplings took place during May 2006, south of Crete, using the HCMR
research vessel “Aegaeo”, within the activities of the project HERMES (Hotspot
Ecosystem Research on the Margins of European Seas). A box-corer sampler USNEL was
used for the collection of samples. The aim of this study was the quantitative and
qualitative assessment of the macrofauna composition at the submarine part of the Samaria
Canyon, as well as at the nearby slopes, the comparison of the stations between the
transects and the correlation of the species present in the sampling areas with the existing
environmental parameters.
The multidimensional scaling (MDS) was used for the analysis of the fauna data,
the ANOSIM method was used for the similarity analysis, and the software SIMPER
Analysis was used for the identification of the characteristic species. The assessment of
diversity was based on the already established methods (diversity indices Shannon-Wiener,
Margalef and Pielou), while for the examination of the relationship between the
macrofauna data and the environmental parameters the method BIO-ENV was used.
The fauna analysis was performed at a species level and indicated 100 species
within a total of 2056 individuals. Although Sipuncula were the dominant taxonomic
group, Polychaetes had the highest species abundance. The dominance of Sipuncula
contradicts with most studies, where Polychaetes appear as the most abundant group.
However, other studies have also indicated that one of the characteristics of the Cretan
shelf is the relatively high abundance of Sipuncula, which can be attributed to their
competitive advantage in oligotrophic conditions. Molluscs appeared down to a depth of
1086 m, while the Echinoderm group was absent from the collected samples. At a species
level, most abundant was the Sipunculid Apionsoma murinae bilobatae, followed by the
Polychaete Pholoides dorsipapillatus and the bivalve Kelliella abyssicola.
The abundance and biomass were reduced in relation to depth, especially at depths
greater than 1000 m. This is a result of the low primary productivity, and thus the reduced
food availability, especially at greater depths. Abundance was higher at the most shallow
sampling station, south of Agia Galini harbor.
The most important factors that seem to define the macrobenthos structure were
depth, organic carbon and the type of sediment, whereas stations at depths between 215
and 2500 m had similar biocommunities. At depths greater than 2500 m, the
biocommunities not only presented differences in comparison to the ones of the more
shallow stations, but also between them. This fact signifies the isolation conditions
observed in deep basins, and therefore, the degree of specialisation regarding the
organisms inhabiting them.
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