Phytoplankton gradients from inshore to offshore waters of the Aegean Sea

Ignatiades, Lydia

Inshore-offshore and north-south gradients of physical (temperature, salinity, underwater light penetration) chemical (nutrients) and biological (chlorophyll a, primary production) parameters have been investigated in the Aegean Sea, Eastern Mediterranean. Data (annual means) collected from the inshore-offshore waters of Saronicos Gulf showed well defined gradients of nutrients (P-PO4 : 0.68-0.14 µM; N-NO3+NO2:1.51-0.85 µM; N-NH3 :2.2-1.05 µM; Si-SiO2 : 4.91-3.94 µM), chlorophyll a, (1.06-0.49 mg.m-3) primary production (2.54-1.46 mgC.m-3.h-1) and depth of the euphotic zone (25-55 m). Data (seasonal means) collected from the north-south pelagic area of the Aegean Sea showed that both regions were oligotrophic having very low levels of nutrients (P-PO4 : 0.03-0.03 µM; N-NO3+NO2: 0.62-0.45 µM; N-NH3 : 0.31-0.12 µM; Si-SiO2 : 1.41-1.67 µM). However, well defined spatial north-south gradients of chlorophyll a (0.33-0.23 mg.m-3), primary production (0.86-0.37 mgC.m-3.h-1) and depth of the euphotic zone (90-120 m) were recorded. The picoplankton predominated and accounted for the 56% to 49% of total chlorophyll a and the 51% to 41 % of total primary production in the North and South Aegean Sea respectively.