Influences of cyclones on chlorophyll a concentration and Synechococcus abundance in a subtropical western Pacific coastal ecosystem

Abstract

The effects of tropical cyclones on seasonal variations in phytoplankton biomass were studied at a station on the northern coast of Taiwan. Water temperature at the study site varied between 17 and 30°C in 1994. Both chlorophyll a concentration and Synechococcus abundance were low in the winter and started to increase when surface water became warmer than 25°C. In July and August, 4 cyclones struck the study site. All cyclones dramatically reduced phytoplankton biomass in the water column, and caused significant increases in nitrate, nitrite, phosphate, and silicate concentrations. Blooms of phytoplankton with total chlorophyll a concentration as high as 4.2 μg l-1 were observed after cyclonic disturbances, and were mainly composed of species greater than 5 μm in size. Our results suggest that cyclones disturb coastal marine ecosystems in a consistent way, and induce ordered and predictable changes in a phytoplankton community.