The purpose of this study is to examine the Polychaetes populations of the mussel Mytilus gallopro6incialis Lamarck 1819 assemblage in Thessaloniki Bay (Perea, Neoi Epivates, Agia Triada) in space and time. Forty-eight Polychaetes species, which belong to 16 families, were identified among 10 593 individuals. The different distribution in space and time can be attributed to the life cycles of the Polychaetes, and also to the various biotic interactions. In general, the abundance follows the succession of the seasons, with some deviations though. Thus, the samples can be divided into two major groups, the winter and summer samples. The structure of the feeding guilds of the Polycheates population was also investigated and 9 different feeding guilds were identified. The microphagous, sedentary Polychaetes were the dominant guild, whilst the carnivores were the most abundant among the macrophagous. No major differences were observed, as regards the composition of the feeding guilds. The study of the structure of the polychaetofauna showed similar diversity with that of other Mediterranean regions. This fact implies that the polychaetofauna of the M. gallopro6incialis assemblages in the Mediterranean Sea has a stable structure and shows a certain resemblance. Furthermore, the polychaetofauna includes species known as capable of living in polluted water as well as others that are more sensitive in such conditions. Therefore, the biomonitoring of the examined regions proves to be essential for obtaining valuable information about the state of their waters. © 2000 Ifremer/CNRS/IRD/É ditions scientifiques et médicales Elsevier SAS Polychaeta / infralittoral / hard substratum / trophic relations / Aegean Sea Résumé-Structure et fonction des Annélides Polychètes des assemblages de Mytilus gallopro7incialis dans le golfe de Thermaikos (mer Egée Nord). Le but de la présente étude concerne l'examen de la population des Annélides Polychètes de la moule Mytilus gallopro6incialis Lamarck 1819 dans la baie de Salonique (Perea, N. Epivates et Agia-Triada) dans ses dimensions spatiale et temporelle. Pour un total de 10 593 individus, 48 espèces de Polychètes ont été déterminées, représentant 16 familles. L'abondance des Polychètes présente des variations en fonction de l'espace et du temps, ce qui est lié à leur cycle de vie, outre des interractions biotiques qui se développent entre les Polychètes et les autres organismes. Les variations de l'abondance suivent la succession des saisons. Ainsi, les échantillons se regroupent en deux groupes principaux, en fonction de la saison. Parallèlement, une étude de la structure des types trophiques des Polychètes a été réalisée. Cette partie de notre étude a mis en évidence la présence de neuf types trophiques. Au groupe principal, appartiennent les microphages, Polychètes sédentaires, tandis que, parmi les macrophages, dominent les carnivores. Les échantillons ne se différencient pas significativement en fonction de la constitution des types trophiques. L'étude de la constitution de la faun...

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Biomonitoring of mussel bed assemblages can provide valuable information about the impact of pollution on hard substrate assemblages. This study of Mytilus galloprovincialis mussel beds in Thermaikos Gulf (northern Aegean Sea) deals with the spatial and temporal structure of the associated fauna. Samples were collected and abiotic factors were measured in two successive years. Common biocoenotic methods were employed to analyze the data. The samples could be separated into three groups, with summer and winter samples being clearly different. A total of 100 species were found: polychaetes and crustaceans were the most dominant taxa. The assemblage shows high diversity with respect to species abundance. Biotic interactions within the assemblage appear to influence its composition, although the total evenness remains unaffected in space and time. The M. galloprovincialis assemblages can be found in clean as well as in polluted waters and, therefore, are of great interest in biomonitoring studies.Keywords Infralittoral · Hard substratum · Mussel beds · Biomonitoring galloprovincialis populations: the piers of Agia Triada (ST1) andPerea (ST2) (Fig. 1). These piers were constructed 25 years ago and are supported by concrete pillars, which comprise the substrate for the mussel beds. At these sampling sites, the M. galloprovincialis populations develop a uniform physiognomic aspect, with large numbers of mussels covering an area that extends from the lower infralittoral zone down to a depth of 2.5 m.

This study deals with the structure of Peracarida populations in four ports in the NW Aegean Sea, Greece, and with the degree this structure is influenced by the particular biotic and abiotic conditions that prevail in the ports. Quantitative samples were taken during summer and winter in two successive years from artificial hard substrates and were analysed using common biocoenotic methods. The examination of approximately 81,250 specimens revealed the presence of 24 Peracarida species, the most dominant of which were Corophium acutum, Leptochelia savignyi and Elasmopus rapax. All species are very common and have been reported from many sites and assemblages in the N Aegean Sea. The ratios of certain Peracarida genera are discussed as possible indicators of environmental health that may be used in long-term biomonitoring programmes on the impact of pollution in harbours.

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