Phytoplankton Abundance and Distribution in Selected Sites of Boracay Island, Malay, Aklan, Central Philippines

This study investigated the impacts of natural and anthropogenic factors on the coastal water quality dynamics in the Island of Boracay, Malay, Aklan, Central Philippines particularly the effects of nutrient pollution on phytoplankton population. The samples were gathered at two month interval for a total of five samplings by filtering 10 liter buckets of surface water through a net with 25 mu m mesh bag. There were 35 identified genera of phytoplankton belonging to four taxonomic groups. Diatoms had 26 genera, cyanophycean and silicoflagellate and dinoflagellates had one and seven genera, respectively. Diatoms were the dominant group with the highest mean density of 1,588 ind.L-1, followed by silicoflagellate at 399 ind.L-1 represented by Tintinnopsis, cynophycean was represented by Trichodesmium at 204 ind.L-1, while the dinoflagellates had 132 ind.L-1 Genera richness was high when N and P concentrations were relatively lower Phytoplankton density was highest in Lugotan Cove and Long Beach where nutrients readings were relatively high. This research clearly demonstrated that the growth of Trichodesmium reaching carrying capacity is an indication that the island ecosystem is near its ecological thresholds. The level of nitrate N acts as the limiting nutrient in the coastal water of the island controlling the growth of Trichodesmium and phytoplankton diversity. Changes in phytoplankton assemblages and density in the coastal waters were associated to variations on intensity and frequency of water mixing along with nutrient loading coming from anthropogenic activities and land uses in the island.