SHORT TERM TEMPORAL & SPATIAL FLUCTUATIONS IN MARINE CYANOBACTERIUM SYNECHOCOCCUS ABUNDANCE IN OLIGOTROPHIC DEEP SHELF WATERS (NORTHEASTERN MEDITERRANEAN)

Abundance of picoplanktonic marine cyanobacterium Synechococcus was monitored weekly over a year period at an oligotrophic deep shelf station in the northeastern Levantine basin (northeastern Mediterranean). In addition to abundance, ambient parameters such as; temperature, salinity, secchi disc depth, total suspended sediment, nitrate+nitrite, phosphate, chlorophyll and phytoplankton were also collected. Population was found most abundant during March & December (1.8 x 10(4) cells/ml) and June & August (1.4 x 10(4) cells/ml) whereas to the lowest counts were retained in October (9.6 x 10(3) cells/ml) and July (1.0 x 10(4) cells/ml Low levels observed in July coincided with the initial phase of an extraordinary upwelling event that lasted for about 10 weeks. Average cell counts at surface (1.8 x 10(4) cells/ml) almost three fold that observed at 100m (6.4 x 10(3) cells/ml). In contrast to homogeneous temperature & salinity profiles, fluctuations in population abundance with depth was observed during winter convectional mixing (January & February). Abundances remained below 1.0x10(4) cells/ml below 50 m due to stratification observed during summer & autumn. Cell abundances ranged from a minimum of 4.9 x 10(3) to a maximum of 4.4 x 10(4) cells ml(-1) with an annual mean level of 1.8 x 10(4) cells ml(-1) at surface. At the lower part of the euphotic layer abundances ranged from a minimum of 3.0 x 10(3) to a maximum of 2.8 x 10(4) cells ml(-1) with an annual mean level of 6.5 x 10(3) cells ml(-1) at 100 m depth. Based on Spearman's rank correlation analysis, a highly significant correlation between Synechococcus abundance and ambient temperature was observed indicating the populations' affinity to elevated temperatures.