Abstract

Spatial changes in the structure of microplanktic assemblages (sarcodines and alveolates) in the surface waters of coastal regions in the central and southeastern Aegean Sea were estimated during late summer to early autumn. Tintinnidae (Ciliophora), as well, Acanthometridae (Radiolaria) and Globiderinidae (Foraminifera) exhibited a higher abundance in the central Aegean Sea, compared to that in the more oligotrophic southeastern area of the same sea. Multivariate analysis revealed that the samples from the eastern Cretan Sea (South Aegean Sea) were highly distinguished from all the others and showed the highest densities of polycystines (Radiolaria), specifically of the families Thalassicollidae, Thalassosphaeridae, Sphaerozoidae (Collodaria), as well as of Actinommidae (Spumellaria) and Theoperidae (Nassellaria). In addition, the families Ceratiaceae and Prorocentraceae (Dinoflagellata) were more abundant in the southeastern than in the central Aegean Sea. It is indicated that the hydrographic conditions prevailing in the eastern Cretan Sea affected the structure of the microplanktic community in the surface layer. It is proposed that the assemblage of the identified radiolarian families belonging to Collodaria, Spumellaria (S) and Nassellaria (N), with a high S/N ratio, could be used as biological proxy of weak upwelling systems in the warm stratified waters of the oligotrophic eastern Mediterranean.

Key words: Eastern Mediterranean, microplankton, sarcodines, alveolates, abundance, oligotrophic ecosystems.