The cell densities of benthic Prorocentrum on the tip, middle and lower regions of seagrass blades, Enhalus acoroides, were investigated during southwest monsoon months, July- August 1999. The seagrass blade samples were taken from two adjacent coves in Taklong Island, Guimaras province wherein one cove is partially drained and the seagrass is exposed during low tide while the seagrass in the other cove is submerged during low tide. The benthic dinoflagellates invariably composed of Prorocentrum constituted 2.2 to 63.2 % of total microbenthic cell populations found on seagrass blades. There were six Prorocentrum species observed and a toxic species, Prorocentrum lima, was dominant during the study. The Prorocentrum cell densities on seagrass blades ranged from nil to 994 cell· cm-2. There were significant differences (p>0.01) in the Prorocentrum cell densities on the three blade regions. Exposure of seagrass during low tide has no significant effects (p>0.01) on the Prorocentrum populations. However, it was observed that few days after a typhoon in July, there was a marked decrease in Prorocentrum densities on seagrass blades. It is likely that a combination of physical factors particularly strong wave action and the separation of withering or decaying tips of seagrass bring about the entry of Prorocentrum into the coastal food web.