Phytoplankton community response and succession in relation to typhoon passages in the coastal waters of Japan

Analyses of past typhoons, tropical cyclones and hurricanes have suggested that global warming may lead to increasing intensities of these episodic events and that the impacts of typhoons on oceanic biogeochemistry will also be augmented. In the present study, daily variations of the physical-chemical environment and phyto-plankton community succession were investigated in Sagami Bay, Japan, after four typhoons, Mawar, Sinlaku, Etau and Malou which occurred in 2005, 2008, 2009 and 2010, respectively. Immediately after the passage of the respective typhoons, salinity decreased and inorganic macronutrient concentrations [NO2 vertical bar NO3, PO4 and Si(OH)(4)] increased. The surge of macronutrients might be attributable to upwelling and terrestrial runoff during Mawar and terrestrial runoff during Sinlaku, Etau and Malou. Relatively large proportions of dinoflagellates occurred during and just after the passage of the respective typhoons. After the dominance of dinoflagellates, chlorophyll a concentrations and phytoplankton biomass increased dramatically and reached their maxima during 4-6 days after the passage of the typhoons, and diatoms dominated the communities. The dominant diatom species were Skeletonema spp. after Mawar and Chaetoceros spp. after Sinlaku, Etau and Malou. The results show that nitrogen to phosphate ratios are tightly coupled to specific nutrient stoichiometry which subsequently governs the succession of dominant phytoplankton taxa.