Tracking and understanding the historical variations in phytoplankton community composition in Sanggou Bay hold significant implications for eutrophication management, environmental quality regulation in aquaculture waters, and provides basic materials and scientific basis for carrying capacity. Based on previous investigations of phytoplankton in Sanggou Bay, we summerized four decades of historical data to analyze the long-term variation trends in community structure and identify the key drivers on the current state. Results show that chlorophyll a (chl a) in surface water increased from inner to outer bay in spring but decreased in autumn and winter, showing notable compositional shifts. Nano-phytoplankton dominated chl a in spring (53%) and summer (71%), while micro-phytoplankton prevailed in autumn (52%) and winter (71%). A total of 57 phytoplankton species (including varieties and forms) from 33 genera were identified, mainly diatoms (40 species) and dinoflagellates (14 species), and diatoms remained the dominant group. Cell abundance of phytoplankton was the highest in summer (276×103 cells/L) and lowest in winter (6.4×103 cells/L). Species diversity indices had no significant seasonal variation. Over the past four decades, chl a dynamics in Sanggou Bay exhibited two distinct phases: a peak in the 1990s followed by a decline after the 2000s due to the shifts in aquaculture practices, stabilizing post-2000 until 2024. Prolonged large-scale raft aquaculture resulted in the decreases in the number of phytoplankton and diatom species and a notable transition toward smaller-sized diatom dominance. The type and density of culture species and culture modes may be the key factors on the community structure and seasonal variation of phytoplankton.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |