Synechococcus production and grazing loss rates in nearshore tropical waters

Temporal variation of Synechococcus, its production (μ) and grazing loss (g) rates were studied for 2 years at nearshore stations, i.e. Port Dickson and Port Klang along the Straits of Malacca. Synechococcus abundance at Port Dickson (0.3-2.3 × 10⁵ cell ml^-1) was always higher than at Port Klang (0.3-7.1 × 10⁴ cell ml^-1) (p < 0.001). μ ranged up to 0.98 day^-1 (0.51 ± 0.29 day^-1), while g ranged from 0.02 to 0.31 day^-1 (0.15 ± 0.07 day^-1) at Port Klang. At Port Dickson, μ and g averaged 0.47 ± 0.13 day^-1 (0.29-0.82 day^-1) and 0.31 ± 0.14 day^-1 (0.13-0.63 day^-1), respectively. Synechococcus abundance did not correlate with temperature (p > 0.25), but nutrient and light availability were important factors for their distribution. The relationship was modelled as log Synechococcus = 0.37Secchi - 0.01DIN + 4.52 where light availability (as Secchi disc depth) was a more important determinant. From a two-factorial experiment, nutrients were not significant for Synechococcus growth as in situ nutrient concentrations exceeded the threshold for saturated growth. However, light availability was important and elevated Synechococcus growth rates especially at Port Dickson (F = 5.94, p < 0.05). As for grazing loss rates, they were independent of either nutrients or light intensity (p > 0.30). In nearshore tropical waters, an estimated 69 % of Synechococcus production could be grazed.