Abstract
Climate change and other anthropogenic stressors are converging on coastal ecosystems worldwide. Understanding how these stressors interact to affect ecosystem structure and function has immediate implications for coastal planning, however few studies quantify stressor interactions. We examined past and potential future interactions between two leading stressors on New England salt marshes: sea-level rise and marsh crab (Sesarma reticulatum) grazing driven low marsh die-off. Geospatial analyses reveal that crab-driven die-off has led to an order of magnitude more marsh loss than sea-level rise between 2005 and 2013. However, field transplant experimental results suggest that sea-level rise will facilitate crab expansion into higher elevation marsh platforms by inundating and gradually softening now-tough high marsh peat, exposing large areas to crab-driven die-off. Taking interactive effects of marsh softening and concomitant overgrazing into account, we estimate that even modest levels of sea-level rise will lead to levels of salt marsh habitat loss that are 3x greater than the additive effects of sea-level rise and crab-driven die-off would predict. These findings highlight the importance of multiple stressor studies in enhancing mechanistic understanding of ecosystem vulnerabilities to future stress scenarios and encourage managers to focus on ameliorating local stressors to break detrimental synergisms, reduce future ecosystem loss, and enhance ecosystem resilience to global change.
Highlights
Multiple anthropogenic stressors increasingly affect ecological systems at the population, community, and ecosystem level [1][2]
Geospatial analyses revealed that healthy salt marshes with little to no history of low marsh die-off have been largely keeping pace with sea-level rise, losing only 0.2 ± 0.1%
At the range of sites experiencing consumer-driven die-off, remaining low marsh area accounts for only 14 ± 3% of the total marsh area (Fig 1A and 1B), suggesting that soft peat availability may become a limiting factor for crab overgrazing and die-off expansion
Summary
Multiple anthropogenic stressors increasingly affect ecological systems at the population, community, and ecosystem level [1][2]. As effects of climate change become more deleterious, a central goal of ecology and conservation biology must be to better understand, predict, and mitigate the effects of these stressors and their interactions on ecosystems [3]. When the effect of two or more stressors is the sum of their individual impacts, they interact additively. Stressor interactions can be non-additive, where the degradation is either greater than (synergistic) or less than (antagonistic) their individual effects would predict. The potential for synergistic interactions is of particular concern as they can lead to unpredictable declines in ecological systems Recent meta-analyses suggest, that despite initial preconceptions about synergisms as ubiquitous traits of stressor interactions, both
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