Distribution of Synechococcus and Prochlorococcus in the central Adriatic Sea

Photosynthetic picoplankton, represented primarily by the genera Synechococcus and Prochlorococcus, are major contributors of biomass and primary production in oligotrophic oceanic ecosystems (JOHNSON & SIEBURTH, 1979; WATERBURY et al., 1979; PARTENSKY et al., 1999a). In the oligotrophic Mediterranean Sea, picophytoplankton has a great contribution to total phytoplankton biomass and production (MAGAZZÙ & DECEMBRI, 1995; AGAWIN et al., 2000). Photosynthetic picoplankton appears to be an essential component of microbial food webs and carbon flow, especially during the summer in coastal systems (KUOSA, 1991; WORDEN et al., 2004). Previous studies in the Adriatic Sea were mainly related to investigations of abundance The abundance of Synechococcus and Prochlorococcus were determined at twenty-one stations located along the eastern coast of the central and southern Adriatic and at three stations located in the open central Adriatic Sea. Synechococcus abundance ranged from 102 to 105 cells mL-1 in the coastal area, and from 103 to 104 cells mL-1 in the open sea. Prochlorococcus abundance in the coastal area ranged from 0 to 104 cells mL-1, and from 103 to 104 cells mL-1 in the open sea. The seasonal distribution of Synechococcus and Prochlorococcus mostly showed an increase in abundance during the warmer period and a decrease during winter. The highest abundance of Synechococcus was found in Kaštela Bay with values at 4.6 x 105 cells mL-1, while the highest abundance of Prochlorococcus was determined in the Šibenik area and recorded as 7.1 x 104 cells mL. Synechococcus was found to be more abundant than Prochlorococcus in most cases. The abundance of Synechococcus was influenced more by temperature than nutrient availability. The abundance of Prochlorococcocus was influenced by nutrient availability and the movement of water masses more than by HNF.