Monthly changes in primary and bacterial productivity in the North – Eastern Mediterranean shelf waters
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Within the context of this thesis, it was aimed to compare monthly changes in primary and bacterial production rates of eutrophic shelf waters with those of nutrient impoverished oligotrophic open waters taking into consideration of ambient physicochemical properties of the basin waters. In addition, size fractionated primary production and limiting nutrient experiments were also carried out. To achieve these goals, a total of 25 cruises were realized on board R/V Bilim-2 of IMS-METU to collect biological (primary and bacterial productivity, size-fractionated primary productivity and chlorophyll a, phytoplankton marker pigments, bacterial abundance, nutrient enrichment experiments), chemical (nitrite+nitrate, silicate, phosphate, ammonium, dissolved oxygen, pH) and physical (temperature, salinity, density, daily surface PAR, Secchi disc depth) data between September 2008 and October 2011 in the basin. 14C and leucine-3H methods were applied to assess primary and bacterial productivity, respectively. Depth integrated primary productivity and bacterial productivity varied between 2.05 – 121 and 0.31 – 3.36 mgCm-2h-1, respectively in the study area. Annual primary and bacterial productivity were estimated to be 151.2 and 14.6 g C.m-2 y-1 for the shelf and 65.4 and 12.9 g C.m-2 y-1 for the offshore, respectively. A highly significant positive correlation was found between bacterial production and chlorophyll a and primary production in eutrophic coastal waters. Phytoplankton at east coast of Mersin Bay had displayed higher carbon to chlorophyll ratio than those in the west. Larger cells (>5µm) have been found to dominate Primary Production (PP) in the western shelf and picoplankters to dominate PP in the eastern shelf. However, in the east, the top 10 m that was affected greatly from the river runoff was dominated by cells larger than 5 µm. From inshore to offshore a gradual increase in picoplankton contribution to the total primary production was observed (% 41.1 to 54.4 to 70.7). Inversely, a gradual decrease in contribution of larger cells to total primary production was observed towards offshore (%44.1, 27.5, 16.1). While large eukaryotes (diatoms and dinoflagellates) dominated the flora in the eastern shelf, all groups seemed to contribute evenly to the bulk throughout the study period in the western shelf in Mersin Bay. Prokaryotic picoplankton (Prochlorophyta and Cyanophyta) and eukaryotic nanoflagellates (Chrysophyta, Chlorophyta and Prymnesiophyta) together formed the bulk of offshore flora where cyanobacteria and prymnesiophyta (coccolithophorids) shifted with each other in time. P was found to be the limiting nutrient for bacterial growth , while P, N and N+P controlled seasonally the growth of phytoplankton in the basin.