SEASONAL CHARACTERISTICS OF MESOZOOPLANKTON IN THE NORTHERNMOST MEDITERRANEAN GULF (GULF OF TRIESTE, ADRIATIC SEA)

The Gulf of Trieste hosts two zooplankton time series one from coastal north-western area (LTER, C1) influenced by freshwaters and one in the south-eastern waters (BF) more influenced by southern waters incoming. We present data on mesozooplankton abundance, structure, biomass and stable isotope ratios obtained at these two locations and during two cruises (March and August 2011) with 16 stations placed on three transects crossing the gulf. The Gulf of Trieste is an important spawning area for anchovies and information about seasonal variations on zooplankton stock and 15N and 13C are fundamental for future studies on trophic food web functioning. In March copepods were numerically dominant while in August also cladocerans (typically present in this area only in summer) were very abundant. Total zooplankton abundance ranged from 1526 to 6507 ind/m3 and 10795 to 30080 ind/m3 in March and August respectively whereas total zooplankton biomass was very similar in the two seasons (mean value: March=30±17mgDW/m3, August=36±18 mgDW/m3). SIA analysis revealed significant differences between seasons with isotopic ratios lower in spring than in summer.