Diatom-dinoflagellate dynamics in marine ranching ecosystems under seasonal shifts and interannual climatic conditions

Global climate events like the El Niño-Southern Oscillation (ENSO) significantly influence ecological dynamics in coastal ecosystems, particularly engineered ones. The health of primary producers such as diatoms and dinoflagellates are vital for engineered ecosystem balance, and understanding their dynamics is essential for effective conservation strategies. This study utilizes long-term monitoring data from 2003 to 2022, employing generalized additive models (GAM) to analyze the spatio-temporal variations of diatom and dinoflagellate abundance in Haizhou Bay, with a focus on the impacts of interannual climate events. The results showed that diatom abundance peaked in October, with significantly lower values in May, indicating strong seasonal variation (P < 0.01). In contrast, dinoflagellate abundance was highest in October and showed less pronounced seasonal differences. Interannually, diatom abundance was highest in 2017 and 2020, while dinoflagellates peaked in 2016 and 2012. Diatoms exhibited a shifting spatial distribution, concentrating in the central and eastern areas during different seasons, while dinoflagellates showed relatively uniform distributions initially, later concentrating in central and northern regions. The spatial patterns were influenced by both seasonal changes and ENSO events. The GAM analysis revealed that diatom abundance was significantly affected by temperature and nutrient availability across different seasons. Under strong El Niño conditions, diatom abundance increased, while dinoflagellate populations remained stable, indicating a competitive advantage for diatoms during these periods. Conversely, dinoflagellate abundance showed no significant variation across interannual events. Our findings underscore the importance of resource availability in shaping phytoplankton communities. Changes in diatoms and dinoflagellate abundance are key indicators of health and stress within the marine ranching ecosystem. This research supports effective management strategies and highlights the need for adaptive practices to enhance coastal engineered ecosystem resilience amid climate change.