Abundance of non-toxic and low-level toxic Pseudo-nitzschia explains the low levels of neurotoxin domoic acid in Chinese coastal waters.

Domoic acid (DA), a well-known marine neurotoxin, is produced by toxic Pseudo-nitzschia species. However, the knowledge of DA in Chinese coastal waters remains limited, and the primary biological sources in these waters are still unknown. In this study, 200 surface phytoplankton samples were collected during summer and spring, covering the entire Chinese coastline. Particulate DA (pDA) was detected in 41 samples, and among these, 34 were from summer, particularly nearshore. The peak content, 230 ng L-1, was in the southern Yellow Sea, followed by 116.6 ng L-1 in the Taiwan Strait, both in July. Multiple methods were employed to trace the biological sources of pDA. The results indicated that the primary producer was P. multistriata in the southern Yellow Sea, but P. cuspidata Clade III in the Taiwan Strait. Temperature was the key factor affecting the composition of Pseudo-nitzschia community, and both primary DA producers showed warm temperature preferences. The levels of pDA in this study was comparatively low, which may be explained by the prevalence of non-toxic Pseudo-nitzschia species and the low DA-production capacity of toxic species under the prevailing environmental conditions. This study represents the first exploration of pDA along the entire Chinese coastline, identifying primary producers and thus enhancing our understanding of DA and toxic Pseudo-nitzschia.