engleski

Fluctuations in the abundance and composition of microphytoplankton off shore Rovinj (the northern Adriatic Sea) in the period 1972-2009

Microphytoplankton as a primary producer plays a major role in the marine food web and can reflect the ecosystems response to long- and short-term changes of external pressures (mainly climatic and anthropogenic). Fluctuations of the microphytoplankton community composition and abundance at two eastern coastal stations of the profile Po Delta - Rovinj (RV001 and SJ107, 1 and 15 nautical miles off Rovinj, respectively) were investigated using the 1972-2009 data series. Analyses of the yearly cycle of phytoplankton groups showed the dominance of dinoflagellates in summer, while during the rest of the year diatoms dominated. A significant variability of the seasonal cycle indicated evident differences among various time intervals of the investigated period. In the interval of 1972-79 three phytoplankton blooms often occurred (February, May-June and September-November). The period 1980-87 was characterized by a single yearly bloom maximum (February-April), while during 1987-1992 two blooms often occurred in period February to June. After 1993, there were 2 blooms per year (February-April and September-November). The data analysis performed on a seasonal base showed an increased appearance of diatom blooms (spring, 1986-2000). At station SJ107 in the 1980’s increased abundances of dinoflagellates were observed during summer. Whereas the group of prymnesiophyceae showed an increasing trend in the period after 1983-1986.

northern Adriatic Sea; diatoms; dinoflagellates; long term changes; microphytoplankton;

nije evidentirano