ANALYSIS OF TEMPORAL CHANGES IN MACROBENT HIC COMMUNITIES ON THE BASIS OF PROBABLE SPECIES PRESENCE

Statistical analysis of long-term changes in marine communities genera lly involves recourse to multivariate methods. Some of these, such as Correspondence Analysis (CA), are very sensitive to the presence of ra re species in the data, whereas other methods, such as Principal Compo nents analysis (PCA) or Multidimensional Scaling (MDS) are only sensit ive to the dominant species. Thus, it is necessary to identify rare sp ecies. We used an original method of species determination, based on a multinomial scheme and permitting the generalization of the classical presence/absence coding from a probabilistic viewpoint. This selectio n method was applied to the identification of the different categories of species (rare, intermediate or dominant) that constitute the muddy fine sand community of the Bay of Morlaix. Multidimensional Scaling w as performed on the Bhattacharrya interdistance table between observat ions, based on dominant species. The results of this analysis were com pared to those of several correspondence analyses carried out on both tables of presence/absence codings (the usual and the generalized ones ).