Characterizing phytoplankton communities is essential to understanding the ecological functioning of pelagic marine systems. Nevertheless, our knowledge of phytoplankton communities is still inadequate for many tropical habitats, including estuaries. It is assumed that highly turbid tropical estuaries often experience acidification due to anthropogenic inputs, microbial degradation, run-off from acidic sulphate soils, and low buffer capacity characteristic for all estuarine systems. Here, we describe phytoplankton communities from the turbid, acidified, and euthrophised estuary of Brunei River (South East Asia). The four selected sampling stations represented gradients of salinity (0.4 – 28.5 PSU) and pH (5.87 – 8.06). A total of 26 microalgal families of phytoplankton (22 genera of diatoms, 7 of dinoflagellates, and 1 of ciliates) were recorded in the survey carried out over one year. The highest density was recorded at an intermediate station along the gradient (up to 9107 cells ml-1), whereas the lowest diversity was found at the least saline and most acidic station (7-1146 cells ml-1). Diatoms were a dominant component of the communities, with Nitzschia spp., Rhizosolenia spp., and Leptocylindrus sp. reaching the highest abundances. Salinity, pH and dissolved oxygen (DO) were positively correlated with the plankton abundances and typically declined landwards. Statistical analyses indicated that phytoplankton communities were strongly influenced by the effect of season (30 % of the total variance in phytoplankton data explained) and sampling site (20 %). The joint effect of pH and salinity and of pH and temperature explained 16.7 % and 17.5 % of the total observed variation, respectively.
Majewska R., Adam A., Mohammad-Noor N., Convey P., De Stefano M. & Marshall D. J., 2017. Spatio-temporal variation of phytoplankton communities along a salinity and pH gradient in a tropical estuary (Brunei, Borneo, South East Asia). Tropical Ecology 58(2):251–269. Article (subscription required).
