Unique distribution pattern of Aureococcus anophagefferens in the Yellow Sea during late summer influenced by complex hydrodynamics and green tide decomposition

Abstract

Since 2009, brown tide-causing pelagophyte Aureococcus anophagefferens has recurrently impacted northern Chinese coastal waters. Previous observations suggest elevated abundances of A. anophagefferens occur in specific regions of the Yellow Sea (YS) where the decomposition of Ulva prolifera green tides during late summer, implying supportive role on its growth for green algae decomposition. However, the complex hydrodynamic processes in these areas complicate the disentanglement of the effects of green tide decomposition and hydrodynamic influences. In this study, quantitative PCR and environmental analyses were employed to examine the spatial distribution, interannual variations, and environmental drivers of A. anophagefferens during late summers in 2016, characterized by a high-intensity green tide, and 2017, marked by a low-intensity green tide. A. anophagefferens exhibited a vertically spindle-shaped distribution with peak cell densities at the deep chlorophyll maximum layer, primarily along the Shandong Peninsula and in the eastern YS. Notably, cell abundances in 2016 were significantly higher than those in 2017, linking to increased ammonium, phosphate, and dissolved organic matter resulting from green tide decomposition. Hydrodynamic factors, especially temperature stratification and the Yellow Sea Bottom Cold Water, appeared to significantly affect the distribution of A. anophagefferens. The enhanced nutrient release during the large-scale green tide event in 2016 further promoted the growth of A. anophagefferens, highlighting the link between green tide events and the emergence of other harmful algal blooms in northern Chinese coastal waters.