Title:

Influence of upwelling on harmful algal blooms

Harmful Algal blooms (HAB) are excessive blooms of monospecific phytoplankton species. Because HABs significantly increase fish mortality, they hamper fishery industries. Kim et al. (2016) pointed out that horizontal advection off the south coast of Korea and coastal upwelling provided nutrients to the surface waters that subsequently led to an anomalous HAB event off the east coast of Korea. Unfortunately, even qualitative assessment of the relative contributions by horizontal advection or vertical upwelling is poorly understood. In this study, numerical sensitivity experiments for the two mechanisms are conducted using a coupled eco-physical model. The simulation results show that HABs are seldomly enhanced by increased upwelling and more strongly depends on horizontal transport from the south coast of Korea. Theoretical analysis suggests that HABs do not responded to upwelling because 1) growth rates of HAB species are not high enough to bloom during upwelling events in small-scale coastal regions, and 2) HAB species are defeated by diatoms through nutrient resource competition, as a result, nutrients provided by upwelling are not consumed by HAB species (only the diatoms).

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