Phytoplankton size-based dynamics in the Aegean Sea (Eastern Mediterranean)

This study represents one component of the large MTP-II-MATER (MAST-III) multidisiplinary project in the Mediterranean supported by EU. Data were collected during three cruises performed in Spring and Autumn 1997 and Spring 1998 from six stations of the North and five stations of the South Aegean Sea. The work assessed the spatial, vertical and temporal variations of size fractionated chlorophyll a, primary production (in situ), photosynthetic parameters (in situ) and the taxonomic composition of phytoplankton. The population structure and dynamics were greatly influenced by the different hydrographic conditions prevailing in the Northern and Southern Aegean Sea due to the influence of Black Sea and Levantine Sea waters, respectively. The picoplankton fraction (0.2-1.2 mum) predominated and accounted for the 56% to 49% of total chl alpha and the 51% to 41% of total primary production in the N. and S. Aegean Sea, respectively. Throughout the sampling area, the levels of nano+microplankton (>3.0 gm) were next in abundance proportions of total chl alpha (21-31%) and primary production (20-33%) and the levels of the ultraplankton (1.2-3.0 mum) were the lowest, contributing the 18-22% of total chl alpha and the 20-23% of total primary production. There was a highly significant (P less than or equal to 0.005-0.01) spatial, vertical and temporal influence on the biomass and productivity of all size classes in the N. Aegean and of most of them in S. Aegean. Light utilization efficiency (s%) and quantum yield (phi(max)) exhibited a temporal trend having higher values in Spring than in Autumn as well as a trend affected by cell size, being higher for picoplankton in relation to ultraplankton and nano + microplankton. Assimilation ratios (P-B) increased with cell size. Daily primary production in the N. Aegean (81.36 mg C m(-2) day(-1)) was higher than that in the S. Aegean (38.88 mg C m(-2) day(-1)) but both are characterized as the most oligotrophic areas of the eastern Mediterranean. (C) 2002 Elsevier Science B.V All rights reserved.