Factors Affecting Variability of Heterotrophic and Phototrophic Microorganisms at High Water in a Mangrove Forest at Cape Rachado, Malaysia

We sampled hourly, surface water in a mangrove forest at Cape Rachado, Port Dickson (in the Straits ofMalacca) on four occasions (4 January , 18 April, 25 July and 29 December, 2003). Water level in this intertidal zone was between 0.3 and 1.6 m. Seawater temperature ranged 28 -33°C whereas salinity ranged 25 -33. Dissolved oxygen (DO) concentration was low ranging between 110 and 270 µM, and reflected a reducing environment (as shown by the negative redox potential, -40 to -70 mV). Chlorophyll a (Chl a) varied between 0.80 -7.0 µg L^-1 whereas ammonium, nitrite, nitrate , phosphate and silicate ranged 0 -6.50 µM, 0.10 -0.80 µM , 0.50 -4.40 µM , 0:-6.70 µM and 8.79 27.27 µM, respectively. For biotic variable s, phototrophic picoplankton abundance was relatively stable, ranging between 1.8 -14.6x10^5 cells mL^-I whereas bacterial abundance was about one order higher, ranging 0.5 -28.4x 10^6 cells mL^-I . Using principal component analysis , we found that the physical condition of the water could account for both ChI a and phototrophic picoplankton variation whereas inorganic nitrogen was important for phototrophic picoplankton. We also showed through nutrient limitation study that phytoplankton was limited by both P and Si. Bacterial abundance correlated significantly with Chl a (R^2=0.288, n=29,p 0.01) indicating bacteria-phytoplankton coupling .