THE HETEROTROPHIC EBRIDIAN MICROFLAGELLATE HERMESINUM-ADRIATICUM ZACHIN THE ADRIATIC SEA

Hermesinum adriaticum ZACH, is a rare non-photosynthetic flagellate wi th an internal siliceous skeleton. It is of uncertain taxonomic positi on and was, recently classified within dinoflagellates (Ebriales). Sub surface accumulation of H. adriaticum ZACH. (UP to 380,000 cells I-1) was found around the brackish/seawater interface (BSI), in a small, sa line coastal lake (Lake Rogoznica, central Adriatic coast), from March to November 1994. Dense populations of this species may be found only in stratified ecosystems with a well defined oxic/hypoxic (anoxic) - H2S enriched boundary layer. In Lake Rogoznica such conditions coincid ed with the BSI. The increasing gradient of phosphate, nitrate, ammoni a and silicate concentrations provided evidence of a sharp chemocline below the BSI. In winter, an advective transport of H. adriaticum popu lation was evident in the southeastern Adriatic; by an inflowing north erly current from the eastern Mediterranean.