Stressor fluctuations alter mechanisms underpinning seagrass responses to multiple stressors

• Published in: Marine pollution bulletin 2025-02, Vol.211, p.117444, Article 117444
• Main Authors: Ostrowski, Andria, Connolly, Rod M., Rasmussen, Jasmine A., Buelow, Christina A., Sievers, Michael
• Format: Article
• Language: English
• Subjects: Anthropogenic impact; Coastal wetlands; Contamination; Light availability; Mechanistic effects; Photosystem II herbicides
• ISSN: 0025-326X; 1879-3363; 1879-3363
• DOI: 10.1016/j.marpolbul.2024.117444

Multiple anthropogenic stressors degrade ecosystems globally. A key knowledge gap in multiple stressor research is how variability in stressor intensity (i.e., fluctuations) and synchronicity (i.e., timing of fluctuations) affect biological responses, and the mechanisms underpinning responses. We evaluated the mechanistic effects of reduced light and herbicide contamination on seagrass, and determined how variations in stressor intensity and synchronicity influence the underlying mechanisms of responses. We used structural causal modelling and structural equation modelling to elucidate direct and mediating effects. Out-of-phase introduction (i.e., asynchronous fluctuations) altered the mechanistic pathways of how stressors affect seagrass relative to static stressors, and resulted in the greatest biomass loss (under the most intense stressor combination, ∼50 % reduction). Therefore, previous experiments that predominantly test only static stressor intensities might underestimate detrimental impacts in nature. Future experiments should explore mechanistic effects across realistic stressor intensities and synchronicities to improve our understanding and management of multiple stressors. •Environmental variability influences stressor intensity and synchronicity.•Photo-physiological responses to stressors mediated impacts on seagrass biomass.•Seagrass lost more biomass when stressor intensity fluctuated.•Asynchronous fluctuations altered mechanisms underpinning seagrass responses.•Experiments with static stressors likely underestimate detrimental impacts in nature.