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Discussion

The fluctuations of the abiotic data between the six sites are indicative of their spe-
cial geomorphological and hydrographical characteristics. The “multicausal environ-
mental severity hypothesis” predicts that different ecological variables may well limit
the populations of different species, rather than a unique master factor acting on the
populations of all species (Brazeiro, 2001). The findings of this study indicate that the
Mediterranean microtidal sandy beach environment is not an exception to the above
hypothesis and are in accordance with the results deriving from the biotic variables
(Papageorgiou et al., 2005).
The application of the Cluster analysis to the sandy beach macrofaunal data de-
monstrated a tentative zoogeographic gradient (referred to as zoogeocline) from the
Eastern (Levantine Basin) to the Western Sectors (Western Mediterranean). How-
Content accessed by IP address 193.188.47.42 on 15/06/2017
ever, there are some cases inconsistent with the above pattern and this is well shown
by the existence of the fourth group, which includes sandy beaches from various
locations along the Mediterranean. Several reasons can be cited to explain the above
cases, the main of which seem to be the different scientific effort spent on these lo-
cations as well as the different scientific expertise existing in each of the sectors. The
latter is further enhanced by the values of the Taxonomic Distinctness Indices: the
fact that many of the sandy beaches taken into account in this study show higher
than expected values is indicative of the less scientific effort spent, which results
in many oligo- or monotypic taxa which, in turn, raise the value of the indices
(Arvanitidis et al., 2002).
The location of the Cretan sandy beaches on the lower parts of the funnels is by no
means in agreement with the high number of species found in these locations. A sim-
ilar situation exists for the Maremma sandy beach when calculation of the Taxonomic
Distinctness Indices is based on the macrobenthic species distribution. Conversely,
the pan-Mediterranean biodiversity pattern changes significantly when the polychaete
species distribution is used. The most plausible explanation for these results would
be that this taxon has recently undergone a phylogenetic analysis which profoundly
changed the interrelationships among the higher taxonomic categories (Fauchald &
Rouse, 1997; Rouse & Fauchald, 1997; Rouse & Pleijel, 2001). Finally, polychaetes
have been proved to be a successful indicator taxon in other transitional ecosystems
in the Mediterranean (lagoons) when utilized for the calculation of the Taxonomic
Distinctness Indices (Arvanitidis et al., 2005a, b).

Acknowledgments

This study was supported by the MEDCORE Project, funded by the EU contract
ICA3-CT-2002-10003. The authors wish to acknowledge Prof. Felicita Scapini for
her encouragement during the stages of this study and Ms Margaret Eleftheriou for