Differentiation of zooplankton communities in two neighbouring shallow areas  <B>Differentiation of zooplankton communities in two neighbouring shallow areas</B><P><B>Ioanna Siokou-Frangou</B><SUP>1</SUP><B>, George Verriopoulos</B><SUP>2</SUP><B>,<BR> Constantin Yannopoulos</B><SUP>2</SUP> <B>& Maria Moraitou-Apostolopoulou</B><SUP>2</SUP><P> 1. <I>National Centre for Marine Research, GR-16604 Hellenikon, Athens, Greece</I><BR> 2. <I>Zoological Laboratory, University of Athens, GR-15874 Athens, Greece</I><B><P> Abstract</B><BR> The annual cycle of zooplankton species composition was studied during two years in two shallow areas of Saronikos Gulf (Greece). Elefsis Bay is a semi-enclosed area receiving a large volume of domestic and industrial effluents. The Metopi area is located in the centre of Saronikos Gulf far away from the pollution sources. In Elefsis Bay the annual cycle was characterized by the extreme dominance of <I>Acartia clausi</I> during the JanuaryMay period of both years, while changes occurred during the summerautumn period as four assemblages were distinguished according to the hierarchical clustering. In the Metopi area species composition was different from that in Elefsis Bay: the winter assemblage was characterized by <I>Clausocalanus pergens, Ctenocalanus vanus</I>, the summer one by <I>Penilia avirostris, Temora stylifera, Clausocalanus furcatus</I>, the autumn by <I>Oncaea media, Oithona plumifera</I> and <I>Paracalanus parvus</I>, while during spring three assemblages were distinguished. Correspondence analysis revealed that the seasonal evolution of the community in the Metopi area can be related to temperature as well as to the influence of the open sea, while the above influences were not obvious in the Elefsis Bay community. Rank-frequency diagrams and diversity index values showed a well-structured community in the Metopi area and a disturbed community in Elefsis Bay. Differences of these two communities could be attributed to pollution impact affecting them differently, coupled with the topography of the area.<I><P> Keywords</I>: zooplankton, shallow, species assemblages, Eastern Mediterranean.<P>