Functional stability of coastal plankton communities toward extreme weather-related stressors

Tanguy Soulié, Francesca Vidussi, Behzad Mostajir

Extreme weather events, such as marine heatwaves and terrestrial runoff, are intensifying in many areas and pose growing threats. In the present study, we assessed the functional stability of plankton communities in response to these events by comparing their responses to marine heatwave and terrestrial runoff stressors. Using two in situ mesocosm experiments conducted at the same coastal site, we examined two key functional balances, namely, the metabolic balance between gross primary production (GPP) and community respiration (R), and the trophic balance between phytoplankton growth (µ) and losses (L). Plankton showed higher resistance to the heatwave than to the runoff, with smaller changes in GPP, R, µ, and L. However, functional resilience was limited after the heatwave, while the community rapidly recovered from the runoff, with overcompensation of all investigated parameters. Respiration responses were similar under both disturbances despite contrasting environmental changes in light, temperature, and nutrients. Our results highlight complex patterns of short-term functional stability in response to extreme events and underscore the need to consider both resistance and resilience when evaluating ecosystem responses to climate change. These insights could inform future monitoring and management strategies for vulnerable coastal waters.