The importance of cryptophytes in phytoplankton community in Xiangshan Bay.

Cryptophytes, as an important phytoplankton group, are usually neglected under traditional microscopical examination. We investigated the spatial and temporal variations of cryptophyte abundances in Xiangshan Bay (XSB) and their importance in the phytoplankton community using data from phytoplankton and environmental factors across four seasons in 2021. We found significant seasonal and spatial differences in cryptophyte abundances in XSB. On the seasonal scale, cryptophyte abundances (cells·mL^-1) showed summer (3944) > winter (2533) > spring (271) > autumn (199). On the spatial scale, cryptophyte abundance showed the lower section (2179) > middle section (1799) > upper section (897). The relative abundances of cryptophytes (61.7% and 43.5%) were higher than those of diatoms (5.7% and 32.1%) in both spring and autumn, and the dominance of cryptophytes (21.9% and 22.3%) was second only to diatoms (76.3% and 74.5%) in winter and summer. Similarity percentage analyses showed that cryptophytes contributed largely (>11.2%) to the seasonal and spatial variations in the phytoplankton community in XSB, which occupied an important position in the phytoplankton community. The genera-lized additive models showed that the seasonal variation in cryptophyte abundances was mainly regulated by tempera-ture and that the spatial distribution was mainly influenced by salinity and dissolved reactive phosphorus. The spatial and temporal variation in cryptophyte relative abundances was mainly regulated by temperature. Our results indicated that the environment with low temperature, low salinity, and high dissolved reactive phosphorus might be more favourable for the growth of cryptophytes in XSB.