Large-scale patterns in summer surface water phytoplankton (except picophytoplankton) in the Eastern Mediterranean

The phytoplankton community structure (except picophytoplankton) and its relationship with environmental parameters were assessed in the surface waters of the Eastern Mediterranean from inshore to offshore areas during the summer for three years. A total of 105 phytoplankton species in six different algal classes, Dinophyceae (54%), Bacillariophyceae (43%), Haptophyceae (5%), Dicthyochophyceae (1%), Euglenophyceae (1%) and Chrysophyceae (1%), were observed in the Eastern Mediterranean. There were three main phytoplankton groups: the aquaculture area (AQ) group, represented by 11 stations; the coastal water (CW) group, represented by 18 stations; and the open-water (OW) group, represented by 43 stations, showing features typical of the Mediterranean coastal and open-water sites and the predominance of dinoflagellate species over other groups in oligotrophic eastern Mediterranean open waters. The OW group had the highest species richness and dinoflagellates were the most important component of these assemblages and there were differences in the dominant groups from the inshore to the offshore waters. Diatom species richness increased while dinoflagellate species numbers decreased in inshore waters that are nutrient-rich due to anthropogenic activities. There were also significant spatial differences in water conditions, including nutrients and water transparency, which were respectively higher and lower between inshore and offshore areas in the Eastern Mediterranean mainly as the result of local anthropogenic factors. Multiple post hoc comparisons (Tukey’s HSD, p < 0.05) showed that the phytoplankton community in the AQ areas had significantly higher values than in the other groups due to the high abundance of coccolithophores, Dactilosolen and Proboshia. Hence, the AQ group presumably exhibited favourable growth conditions along the coastal area. Furthermore, the community structure of the CW group was more similar to OW (p > 0.001, R = 0.25) as several coastal stations were not affected by human activities and exhibited a relatively open-water character due to their hydrological conditions.

Research highlights► The Eastern Mediterranean Sea is considered as one of the less productive seas. ► 105 phytoplankton species were determined in The Eastern Mediterranean Sea. ► Shifts were observed in dominant groups towards the inshore than the offshore waters. ► Inshore water had higher nutrient values and lower water transparency. ► The fluctuation in nutrient concentration was due to local anthropogenic factors.