DIVERSITY AND STRUCTURE OF PELAGIC COPEPOD POPULATIONS IN THE FRONTALZONE OF THE EASTERN ALBORAN SEA

During the oceanographic campaign, ALMOFRONT I (April 24-May 26, 1991) a total of 50 vertical zooplankton hauls was carried out in the Albor an Sea using a triple net. Leg A (18 stations; 18 hauls) described a w idely spaced grid in the region of the Atlantic current and some north ern eddies, while Leg B (16 stations; 32 hauls, 6 hydrodynamically cha racterized sites sampled during a two day period) covered a more restr icted area in the frontal zone. Ninety-one species of copepods were fo und in 100 samples collected by either 200 mum or 500 mum mesh size ne ts, including 32 genera and 26 families. Copepod abundance, structure indexes (species richness, evenness, Shannon species diversity index, standardized for unequal sample counts) and species abundance patterns (as rank-frequency diagrams) are presented and compared among the sit es of leg-B. Copepod abundance was found to be the highest in the more productive sites of the Atlantic current. Structure indexes values an d the changing shape of rank-frequency diagrams give a coherent view o f the ecological succession stages of the copepod community. Juvenile stage (1) develops from the Atlantic divergence zone, left side of the jet. More mature stages (1' and 2) occur on the right side of the jet influenced by cross frontal flow. Both abundance and structure indexe s decrease within an anticyclonic gyre south to the current. A situati on more influenced by oligotrophic conditions was observed in a Medite rranean anticyclonic gyre north of the current. The importance of late ral displacement and meandering of the Atlantic current across the Alb oran Sea to the community structure is discussed.