Dynamics and size structure of phytoplankton in the coastal waters of Singapore

In this paper, a study on phytoplankton dynamics and size in the tropical coastal waters of Singapore is presented. Chlorophyll-a levels in the Singapore Strait generally range from 0.4 to 10 μg l–1, with an average value of 1.7 μg l–1. In general, higher chlorophyll concentrations are typically found off the east coast of Singapore, as well as in the shallower, more protected waters of the Johor Strait (maximum ~78 μg l–1, average = 21.5 μg l–1). Seasonal trends in chlorophyll and nutrients are also apparent, with higher chlorophyll generally observed during the south-west monsoon compared with the wetter north-east monsoon. Size-fractionated chlorophyll measurements of the phytoplankton community show that for low standing stocks of chlorophyll less than 3 μg l–1, approximately 40% of the phytoplankton lies in the pico- and small nanoplankton (<8 μm) size range. As total chlorophyll levels in the system increase, the relative contribution from the larger size classes (i.e. 8–20 and 20–100 μm) increases, with a subsequent decrease in the smaller size classes. For total chlorophyll greater than 40 μg l–1, it was found that the 20–100 μm size class contributed 60% of total chlorophyll. In contrast, the <8 μm size class contributed only about 5% of total chlorophyll for these waters.