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The vertical distribution (0-300 m) of a numerically important group of small and morphologically similar calanoid copepods (Clausocalanus, Ctenocalanus, and Paracalanus) of the families Pseudocalanidae and Paracalanidae is described from a series of hauls taken in six areas of the eastern Mediterranean Sea during a synoptic survey in October/November 1991. A niche separation by partial depth segregation of the species has been observed. The median depth in the total sampling area of the adult females of the species was: Clausocalanus furcatus (26 m), Paracalanus denudatus (30 m), Clausocalanus mastigophorus (41 m), Clausocalanus arcuicornis (67 m), Clausocalanus paululus (72 m), Clausocalanus pergens (95 m), Ctenocalanus vanus (98 m) and Clausocalanus parapergens (113 m). Adults were found in the same depth layer or slightly deeper in the water column than the corresponding copepodid stages. No statistically significant difference (ANOVA, P > 0.05) was detected among the median depths of the species in the six areas sampled, i.e., Sicily Channel, Ionian Sea, Cretan Sea, Levantine Sea, Rhodes area, and Cretan Passage. La répartition verticale (0-300 m) d'un groupe numériquement important de copépodes calanoïdes de petite taille et morphologiquement similaires (Clausocalanus, Ctenocalanus, et Paracalanus) des familles Pseudocalanidae et Paracalanidae, est décrite à partir d'une série de prélèvements effectués dans six zones de la Méditerranée orientale au cours d'une étude synoptique en octobre/novembre 1991. Une séparation des niches par ségrégation partielle des espèces, liée à la profondeur, a été observée. La profondeur moyenne dans la zone totale d'echantillonnage des femelles adultes des différentes espèces est: Clausocalanus furcatus (26 m), Paracalanus denudatus (30 m), Clausocalanus mastigophorus (41 m), Clausocalanus arcuicornis (67 m), Clausocalanus paululus (72 m), Clausocalanus pergens (95 m), Ctenocalanus vanus (98 m), et Clausocalanus parapergens (113 m). Les adultes ont été trouvés dans la même couche de profondeur ou légèrement plus profondément dans la colonne d'eau que les stades copépoditiques correspondants. Aucune différence statistiquement significante (ANOVA, P > 0,05) n'a été détectée dans les profondeurs moyennes des espèces pour les six zones échantillonnées, i.e., détroit de Sicile, mer Ionienne, mer de Crète, mer du Levant, région de Rhodes et passage de Crète. [ABSTRACT FROM AUTHOR]

Mesozooplankton group composition was examined in the Northeastern Aegean Sea (NEA) over a grid of 30 stations sampled during July 2004. The surface water layer influenced by the low salinity Black Sea waters (BSW) is considered in this paper. We attempted to study horizontal distribution patterns of major mesozooplankters within a more comprehensive framework, taking into account not only hydrology but also available, concurrently collected data on lower trophic levels (autotrophic and microbial heterotrophic communities). BSW was mainly restricted in the eastern part of the surveyed area where it was entrapped in a ca. 50-km wide anticyclone (the “Samothraki” gyre). High Chl α concentrations, autotrophic biomass as well as abundance and biomass of mesozooplankton were associated with the BSW, with the highest values recorded inside the gyre as well as at its coastal northern periphery and the lowest values towards the western and offshore part of the surveyed area characterized by high salinity waters of Levantine origin. Among mesozooplankters, cladocerans (mainly Penilia avirostris) showed a high abundance within the gyre in contrast to the very low abundance of copepods and appendicularians. Low salinity-high temperature gyre waters were characterized by the dominance of cyanobacteria of the genus Synechococcus in autotrophic biomass and the significant contribution of heterotrophic nanoflagellates in microbial heterotrophic biomass. Based on existing knowledge on ecophysiological traits and prey size-spectra selectivity, we discuss the observed distribution patterns of major mesozooplankton groups in terms of ambient abiotic parameters and the possible biological interactions among these groups as well as with lower or upper trophic levels. [ABSTRACT FROM AUTHOR]