Population?specific resilience of <i>Halophila ovalis</i> seagrass habitat to unseasonal rainfall, an extreme climate event in estuaries

Extreme climate events are predicted to alter estuarine salinity gradients exposing habitat-forming species more frequent variations. The intensity and duration of these variations, rather than the mean values ecosystems exposed to, may be important in influencing resilience but requires further investigation. Precipitation, including frequency, timing occurrence, is shifting due change. A global analysis on rainfall catchments was conducted. In 80% case studies, maximum daily occurred dry season at least once over 40-year period could classified as an extreme event. We selected estuary southwestern Australia investigated effects event 2017 resulting excess discharge freshwater seagrass Halophila ovalis. Adapting approach applied for marine heatwaves using data, we quantified metrics characterised along gradient. assessed by calculating resistance times based comparisons biomass leaf density data prior during event, recovery through assessment against historical condition. Where historically variable, reductions were lower (higher via plasticity tolerance) meadows recovered within 9–11 months. stable, loss greatest (low resistance) post-event exceed 22 months, potentially rapid decline (?3 PSU/day). As estuaries become hydrologically provide a baseline retrospective future comparisons. Our results suggest hyposalinity population specific. This understanding enables accurate predictions about ecological responses change identifies which populations ‘future proof’ ecosystem resilience. Synthesis. Following found that variable salinities while those from stable environment unable recover study time frame. These findings expand upon existing evidence, derived primarily other ecosystems, show new sources uncovered accounting between-population variation.