Investigating mechanisms for the variability in phytoplankton assemblages in the northeastern waters of the Philippines

The northeastern side of the Philippines, particularly off of Luzon Island, is strongly influenced by the Pacific Western Boundary current system. The North Equatorial Current bifurcates offshore feeding into the Mindanao current flowing south and the Kuroshio Current that begins to consolidate in the waters off of Luzon. Two cruises were conducted during May/June 2011 and April/May 2012 which showed distinctly different circulation patterns and strengths of water masses. Phytoplankton abundances and composition measurements were obtained using microscopy, as well as through an in situ fluorometer. Analysis of the phytoplankton assemblages from these two cruises showed variability in both space and time. Distinct assemblages could be observed amongst different water masses both in 2011 and 2012. There was also a significant difference in the phytoplankton abundances and composition seen between the two sampling years. Mechanisms such as circulation patterns and related physico-chemical characteristics leading to these spatio-temporal variabilities in phytoplankton concentrations and distributions are explored in this study. These shifts in primary producers and productivity have important implications in this region which is a key fishing area for both municipal and commercial fisheries.