Ecological thresholds of phytoplankton community across environmental gradients in the harmful algal blooms-frequently-occurring, subtropical coastal waters, East China Sea

Phytoplankton communities can response immediately and directly to environmental changes, and thus have been applied as reliable biotic indicators in aquatic systems. This study provided insights into the relationships concerning ecological thresholds of phytoplankton communities and individual taxon in response to environmental changes in coastal waters of northern Zhejiang Province, East China Sea. Results demonstrated that there existed seasonal variations of phytoplankton community ecological thresholds of which spring being higher than those in summer. As for individual species, Prorocentrum donghaiense and Noctiluca scintillans were identified as the most tolerant and sensitive indicator species in spring and summer, respectively. They exhibited strong indications in response to environmental changes. These findings highlighted that phytoplankton community structure in this region was stable when environmental gradients were below the thresholds of sensitive species, whereas potential harmful algal blooms may occur when environmental gradients exceeded the thresholds of tolerant species.