Diversity of Coastal Phytoplankton in Balayan Bay, Batangas, Philippines

Abstract

Phytoplankton composition, density, and their relation with 10 abiotic water parameters in six coastal stations [four marine (Anilao, San Luis, Calatagan, and Balayan) and two freshwater (Palanas and Pansipit)] in Balayan Bay, Batangas, Philippines were examined monthly for one year (February 2006–January 2007). A total of 97 taxa of phytoplankton in four phyla were observed. About 85% of these taxa were diatoms (Bacillariophyta). The mean monthly density of phytoplankton ranged from 2,367 (Pansipit Station) to 2,992 units · mL–1 (San Luis Station), with as much as 93% of the total phytoplankton density being made up of diatoms. Cyclotella meneghiniana, a centric diatom, had the highest mean monthly density (143 units · mL–1) in all the stations. Among the six stations, the marine stations generally showed higher phytoplankton density (maximum monthly value = 4,700 units · mL–1, Anilao, in January), species diversity index (maximum monthly value, H’ = 1.402, Balayan, in March), and species richness (maximum monthly value, 29, Balayan, in March) than the freshwater stations. Clear differences were also detected in the physico-chemical characteristics between the freshwater and marine stations. Among the 10 abiotic parameters monitored, mean monthly salinity ranged from 0.92–1.02 psu in freshwater stations and 29.1–32.6 psu in marine stations. Mean monthly water temperatures ranged from 23–33.5 °C and pH ranged from 7.87–8.23. Conductivity in the two freshwater stations ranged from 2,006.17–2,051.92 μS · cm–1 and was 45x of that of the marine stations, which ranged from 44.57–50.48 μS · cm–1. Generally, marine stations showed higher values of total solids, total dissolved solids, and total suspended solids than the freshwater stations. However, marine stations recorded greater water clarity than the freshwater stations (mean monthly depth of Secchi disc ranged from 1.68–3.65 m). Freshwater stations recorded higher mean monthly orthophosphate-P values but generally lower nitrate-N values than the marine stations. These values (1.65–4.31 ppm PO4-P or 0.29–1.41 ppm P; 2.58–5.35 ppm NO3-N or 0.428–1.509 ppm N) are within or near the Philippine standard value of 1.0 ppm for P and N for clean marine water. Changes in some of these abiotic parameters were correlated with changes in the population density of some of the dominant species, to total mean monthly phytoplankton density, species diversity index, and species richness in some of the stations, but no single parameter can explain the biological patterns observed for all stations. No algal bloom was observed during the course of this study, although a potentially harmful dinoflagellate, Ceratium furca, was observed. It was never a dominant alga in any of the stations.