Surface Phytoplankton Assemblages and Controlling Factors in the Strait of Malacca and Sunda Shelf

Abstract

In the context of global warming and climate anomaly events, as a response, shifts in phytoplankton phenology were observed in the Strait of Malacca (SM) and Sunda Shelf (SS). Such interactions between phytoplankton structure and physico-chemical factors were less known in narrow straits. Therefore, the spatial distribution pattern and diversity of surface phytoplankton assemblage, local hydrology and nutrient regimes were investigated over the Strait of Malacca and Sunda Shelf (South China Sea, SCS) during 2017 and 2018 pre-monsoon season (spring). Diatoms, dinoflagellates and cyanobacteria were representatives of microphytoplankton in the survey area. Total phytoplankton abundance peaked near Singapore Strait (SGS) and diminished towards SS. From the lower ratio of diatoms to dinoflagellates (<3) in SS, we deduced lower carbon pump efficiency here. In agreement with the modeled results proposed previously, diatoms (especially centric form) tended to thrive in cold eutrophic water, while, dinoflagellates and filamentous cyanobacteria were much warm-adapted, they operated a feedback to cold La Nina event (negative Indian Ocean Dipole, IOD) in 2018 and warm El Nino event (positive IOD) in 2017, respectively. Specifically, diatom proportion increased by 30% and dinoflagellate, cyanobacteria reduced by 71%, 75% in response to shifts of climate anomaly from 2017 cruise to 2018 cruise. This interactive study between field microalgae and physico-chemiscal conditions would be helpful to launch large-scale climate model, biogeochemistry and carbon cycling in future research.