Effects of Nutrient Enrichment on Coastal Phytoplankton Composition and Abundance in the Northeastern Mediterranean

The response of coastal phytoplankton community to increased nutrient concentrations was examined over a period of 20 days in the summer period on the NE Mediterranean coast. Two different nutrient enrichments were performed. The enrichment treatments received N, P and Si at a ratio of 15 N: 5 Si: 1 P. Two different doses of nutrients (1x and 2x) were applied. The abundance and biomass of the phytoplankton community were also examined in control units to which no nutrients were added. The increase in phytoplankton abundance and biomass were observed in all treatments including the controls 3 days after the initiation of the experiment. The biomass of phytoplankton in terms of chl a increased to a maximum level of 10.6 μgl on 11 day of the experiment in the 2x treatment. The structure of the phytoplankton community shifted from an initial dominance of diatoms to small flagellates. Microphytoplankton abundance reached its maximum level of 33.7x10 cells l in the 1x treatment 13 days after the initiation of the experiment whereas small flagellates reached their maximum abundance as 33.4x10 cells l in the 2x treatment on day 17. From the results obtained, it can be suggested that nutrient enrichment could affect biomass of phytoplankton rather than species composition.