Phytoplankton Blooms in Black Sea and Mediterranean Coastal Ecosystems Subjected to Anthropogenic Eutrophication: Similarities and Differences

Abstract

The similarities and differences in phytoplankton response to anthropogenic nutrient enrichment were studied in coastal sites of the Western Black Sea and the Eastern Mediterranean (Aegean Sea). Although by physico-chemical parameters, two different environments have been compared, the two regions exhibited similar features: 14 common bloom species in the list of bloom producing algae, the highest rate of occurrence and variety of microalgae involved in summer, the highest average level of competitors-strategies species during the summer outbursts, the similar range of maximum bloom densities attained, and similar capacity to sustain critical biomass during all seasons. The low taxonomic similarity (Bray-Curtis index lower than 30%) between the different basins and among sites, could be attributed to both natural factors and dissimilarities and to the gradients in nutrient levels and their ratios, as affected by the different nature and severity of the anthropogenic pressures on the coastal ecosystems. The results of the PCA analysis indicate that temperature and salinity are factors contributing to the differences outlined between the Aegean Sea and the Black Sea ecosystems, but the differences among the selected sites give support to the importance of nutrients and their ratios. Although competitive outcomes in phytoplankton species selection and succession cannot yet be predicted, the analysis suggests that anthropogenic nutrient enrichment could play an important role in driving the phytoplankton bloom performance. The comparative studies between different basins could be a step forward to highlight common patterns and modes of ecosystem response to anthropogenic eutrophication and to suggest common indices to scale eutrophication impact.