Nonlocal Population Sources Triggering Dinoflagellate Blooms in the Changjiang Estuary and Adjacent Seas: A Modeling Study

Dinoflagellates frequently cause harmful, large-scale spring algal blooms in the Changjiang Estuary and adjacent seas of China. However, the population source of some dinoflagellates in this area remains unknown. We deployed an adjoint model and a coupled physical-biological model to explore the possible nonlocal dinoflagellate population sources to the Changjiang Estuary and adjacent seas. Our simulation results revealed that the Taiwan Strait and the area east of Taiwan are two nonlocal source regions of May dinoflagellate blooms in the study area. Under different hydrodynamic and biochemical conditions, dinoflagellates from the Taiwan Strait directly triggered dinoflagellate blooms from south to north along the coast of China. Dinoflagellates from the area east of Taiwan first concentrated and bred in the offshore temperature frontal area and then spread southwestward, triggering dinoflagellate blooms along the Zhejiang coast. Due to the different influence mechanisms, it took longer for the initial dinoflagellate population in the Taiwan Strait to exert the same impact on dinoflagellate blooms in the study area as that from the area east of Taiwan. Moreover, the density and appearance time of the initial dinoflagellate population in the Taiwan Strait affected their biomass and bloom range in the study area. Even a small initial dinoflagellate population east of Taiwan could trigger a bloom in the study area. This study suggests the target domains for finding nonlocal dinoflagellate cysts and provides a strategy to predict dinoflagellate blooms in the Changjiang Estuary adjacent area by monitoring dinoflagellate biomass in the nonlocal source regions.

Automated summary

The study identified the Taiwan Strait and the area east of Taiwan as two nonlocal source regions of May dinoflagellate blooms in the Changjiang Estuary and adjacent seas. Dinoflagellates from the Taiwan Strait directly triggered blooms along the coast of China, while those from the area east of Taiwan first concentrated and bred in offshore temperature frontal areas before spreading southwestward to trigger blooms along the Zhejiang coast.