COMMUNITY VERSUS BIOCOENOSIS IN MULTIVARIATE ANALYSIS OF BENTHIC MOLLUSCAN THANATOCOENOSES

Abstract

Community and biocoenosis as descriptive units for benthic ecology are not perfectly interchangeable. Although the conceptual framework based on communities, originally defined by a statistical quantitative approach, appears to be the most suitable in the statistical treatment of thanatocoenoses data, this framework appears to oversimplify the picture of the most important ecological units in the Mediterranean benthos. On the contrary, the benthic bionomy with the biocoenoses, identified by a group of characteristic species (disregarding their abundance) derives from a qualitative approach which has been more successfully adopted for the research in the Mediterranean area. A group of twelve thanatocoenoses from the Tyrrhenian Sea has been treated with both approaches with the aim to identify a practical strategy for analysing multispecies distribution patterns in benthic paleoecology, trying to combine the advantages of both quantitative and qualitative approaches. When dealing with large-sized data matrices of benthic thanatocoenoses, it is recommended to use a qualitative approach for data reduction, on the basis of their significance in benthic bionomy, prior to perform the quantitative multivariate analysis (classification, ordination, similarity and dissimilarity analysis). This procedure appears to be the most suitable for the identification of “natural” grouping of biotopes, since the results are not obscured by the diffuse occurrence of the most common and ubiquitous species.