The Atlanto-Mediterranean holothurian Holothuria tubulosa is among the conspicuous benthic invertebrates in the shallow sublittoral zone. It is an edible species, harvested at the Aegean Sea and utilized as fishing bait. Considering the lack of information for the Aegean populations, a one-year survey, based on monthly or semimonthly samples, was carried out focusing on population structure, allometric relationships and reproductive status of H. tubulosa stocks in Pagasitikos Gulf. Population density varied around 9.93 individuals/100 m2. This value was rather low compared with other studied Mediterranean populations of the species, possibly due to the scarcity of seagrass meadows in the area studied. All measured biometric characters showed high plasticity, and all the examined morphometric relationships followed negative allometry indicating a change to the shape of the animal's body as it grows. Holothurians’ length was a moderate predictor of biomass since r values reached 60%; in contrast a very strong relation was observed between drained and gutted weight. Size–frequency distribution analysis was unimodal with the exception of spring where a second mode of larger sized individuals appeared. The gonadosomatic index showed a single spawning season per year, in late summer; accordingly the reproductive cycle of the species showed a clear annual pattern which was highly correlated with the seasonal variations of temperature.

Scientific information on the biodiversity of marine caves in the eastern Mediterranean is limited, especially when considering the extensively studied caves of the north-western and central Mediterranean. Aiming to enhance current knowledge regarding cave communities, this study represents a first assessment of the marine cave biota of the eastern Mediterranean, as defined by the European Union's Marine Strategy Framework Directive (MSFD). Information retrieved from an extensive overview of relevant scientific documents was combined with original data recorded from 23 marine caves in the north-eastern Mediterranean. Our results report a total of 520 taxa recorded in eastern Mediterranean marine caves to date, the majority of which are sponges, polychaetes, rhodophytes, bivalves, fishes, and gastropods. These include several protected, endemic and alien species. However, not all taxonomic groups from different areas have been equally investigated and future studies are expected to increase the number of endemic and alien species. The observed general trend is that the reported species number is generally related to sampling effort and scientific expertise. The most well-studied marine cave communities in the eastern Mediterranean are those of the Aegean Sea (especially its northern sector), which presented the highest number of species, followed by those of the Levantine. Furthermore, our research in Aegean caves revealed numerous new records for the marine cave fauna of the eastern basin, while several species are reported for the first time in a marine cave habitat. The critical need for further scientific research, monitoring, and conservation of this unique ecosystem was highlighted by (i) the presence of certain species endemic to the eastern Mediterranean coupled with a high proportion of alien species, especially in the Levantine Basin, and (ii) marine cave habitat availability in isolated insular areas of the eastern Mediterranean.

The associated macrofauna of four Aegean Sea sponge species (Apelas oroides, Petrosia ficiforrnis, lrcinia variahilis and Aplysina aerophoha) was compared. The total number of individuals and species was found to be related to sponge volume for all sponge species.The associated macrofaunal weight per individual on all sponge species was negatively correlated with sponge volume. Sponge complexity, as measured by sponge surface area to biomass ratio, was not a consistent predictor of associated macrofauna abundance or diversity. Sponge macrofauna species were not host specific and their relative abundances differed among sponge species.

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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...