Temperature and nutrient availability are pivotal drivers of coastal phytoplankton dynamics; however, how they regulate the interplay between community assembly and ecological network stability remains less explored. In this study, we integrated 18S rRNA high-throughput sequencing with molecular ecological network analysis and the iCAMP model to investigate the seasonal succession and driving mechanisms of phytoplankton in a coastal region (Qiongdong) of the South China Sea. Our results suggest that water temperature is a key factor influencing community succession. However, rather than following a linear response to temperature rise, the molecular ecological network exhibited a significant network contraction in spring, characterized by minimized complexity and peak vulnerability. This structural shift coincided with a transition in nutrient limitation (from phosphorus to nitrogen) induced by spring upwelling. Assembly process analysis revealed that while stochastic processes dominated overall community construction, a notable increase in dispersal limitation occurred in spring. The intensification of dispersal limitation driven by changes in the nutritional structure may be the main cause of network simplification and reduced stability. In conclusion, our findings highlight that while temperature affects the seasonal replacement of phytoplankton species, nutrient-induced shifts in assembly mechanisms degrade ecological network integrity in coastal environments.
Shi et al. (Fri,) studied this question.