The Heterotrophic Ebridian Microflagellate Hermesinum adriaticumZach. in the Adriatic Sea

Hermesinum adriaticumZach. is a rare non-photosynthetic flagellate with an internal siliceous skeleton. It is of uncertain taxonomic position and was, recently classified within dinoflagellates (Ebriales). Subsurface accumulation of H. adriaticumZach. (up to 380,000 cells - I₋) was found around the brackish/seawater interface (BSI), in a small, saline 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 coincided with the BSI. The increasing gradient of phosphate, nitrate, ammonia and silicate concentrations provided evidence of a sharp chemocline below the BSI. In winter, an advective transport of H. adriaticum population was evident in the southeastern Adriatic; by an inflowing northerly current from the eastern Mediterranean.