Classification and Interpretation of the Established Mediterranean Biocoenoses Based Solely on Bivalve Molluscs

Abstract

Based on the bivalve fauna known from an extensively studied zone, along the infralittoral in the Patras Gulf, a biotope approach was attempted using numerical taxonomy methods. The efficiency of various combinations of similarity measures and clustering techniques is discussed for this type of data (single group – binary). Four main station groups were delimited which were further assigned to the biotopes of known Mediterranean biocoenoses. The four groups correspond to: (a) the biotope of the Posidonia beds (HP) and that of coarse sands and fine gravels under the influence of bottom currents (SGCF). The limits of these two biocoenoses are not clear-cut, (b) The biotope of the coastal detritic bottoms (DC) usually occurring in deeper areas but met in the infralittoral under environmental stress, (c) A transitional zone where degenerating Posidonia meadows are gradually replaced by Cymodocea and Zostera, facies of the muddy sand in sheltered areas biocoenoses (SVMC). This degradation can be attributed to various disturbing factors including natural environmental changes, (d) The biotope of fine well-sorted sands (SFBC). A typical malacofauna is present with the addition of some species. Regardless of the differences, Pérès & Picard's (1964) scheme is more appropriate in the Mediterranean ecosystems than any other northern European scheme.