Dinoflagellate cyst composition, abundance and horizontal distribution in Bolinao, Pangasinan, Northern Philippines

This paper constitutes the first cyst record of a eutrophic tropical mariculture area with harmful algal blooms since 2002 and provides contribution to the global record on dinoflagellate cysts, specifically from Northern part of Southeast Asia. Surface sediment samples from 54 stations in October 2006 and 5 stations from 2004 to 2006 Bolinao, Pangasinan were processed palynologically and by fluorescent techniques. Exploratory data analysis using Two-Way Indicator Species Analysis (TWINSPAN) to identify major patterns of distribution and Canonical Correspondence Analysis (CCA) ordinated stations and species along sediment and environmental variables have been done to determine spatial variations in community structure. Thirty-six cyst types have been identified which include the toxic species, Alexandrium minutum. Species richness and diversity correlated with silt, mud, carbonates and depth but have been observed to be generally low in the area (p < 0.05). Multivariate analysis shows that sediment grain size, nutrients and water depth are important variables related to cyst distribution. Two accumulation points that can be source and sinks of blooms have been identified. The decrease in species richness and diversity of dinoflagellate cysts from 2005 to 2006 has been attributed to intensive mussel farming. Heterotrophs have dominated during the northeast and southwest monsoon seasons while autotrophs which included A. minutum, have dominated during tradewinds. Results indicate that the cysts accumulation points could possibly seed blooms particularly during the tradewinds season and thus should be monitored effectively to prevent negative public health impacts.

► Thirty-six dinoflagellate cysts identified in Bolinao, Pangasinan.
► Sediment grain size, nutrients and water depth as main factors that influence cyst distribution.
► Two accumulation points of Alexandrium minutum that can be source and sinks of harmful algal blooms.
► Accumulation points could possibly seed blooms when trade winds prevail.