Phytoplankton community structure in Singapore's coastal waters using HPLC pigment analysis and flow cytometry

To investigate phytoplankton distributions in the coastal waters of Singapore, seawater samples from the Singapore Strait and the Johor Strait were analysed by high performance liquid chromatography and flow cytometry. Chlorophyll a (Chl a) concentrations were generally high, accompanied by significant amounts of fucoxanthin. Chlorophyll b and other major carotenoids, including zeaxanthin and alloxanthin, were also dominant in the Singapore Strait but were undetectable at most stations in the Johor Strait. Using ratios of Chl a to pigment that were characteristic of the different algal classes, it was shown that diatoms comprised similar to72% of the total Chl a in the Singapore Strait, whereas in the Johor Strait they comprised 88%. Synechococcus contributed another 18% of total Chl a in the Singapore Strait but was insignificant in the Johor Strait. Besides providing rapid enumeration of total phytoplankton, flow cytometric analysis was able to discriminate successfully two different types of Synechococcus ('bright' and 'dim') in the Singapore Strait based on their different orange fluorescence characteristics under blue light excitation. However, no 'bright' Synechococcus was found in the Johor Strait. Overall, the higher biodiversity of the phytoplankton community as well as the lower cell concentration and biomass in the Singapore Strait reflect a more oligotrophic/mesotrophic condition than the Johor Strait.