Differences in bed elevation shape subtidal mussel bed stability under high-energy hydrodynamic events

Escalating high-energy hydrodynamic events, like storms, represent a significant manifestation of global climate change, causing detrimental impacts on various ecosystems and potentially triggering thresholds that result in abrupt shifts in ecosystem states. Despite the potential of such thresholds, few studies have explicitly addressed them. This gap is particularly notable for subtidal ecosystems due to technological challenges in detecting responses of organisms enduring constant submersion. This study focused on subtidal soft-bottom mussel beds through the development of Biophys loggers for in situ monitoring of the fine-scale behavior of mussel clusters under hydrodynamic disturbances and a statistical model based on an 11-yr dataset to perform regional-scale assessments of mussel bed stability. Multisite monitoring in the Dutch Wadden Sea revealed spatial heterogeneity in mussel bed mobility threshold (i.e., near-bed orbital velocity inducing mussel movement), with predictable patterns along elevation gradients. Stability assessment in this region demonstrated that mussel beds in shallower areas (i.e., at higher bed elevations) exhibited higher stability than those in deeper areas, a difference that was attributed to the longer return interval of the mobility thresholds in shallow regions. These findings suggest that conditions such as bed elevation can modulate the stress tolerance of mussels and thereby influence the stability of subtidal soft-bottom mussel beds. This study provides an approach for assessing mussel bed stability, which can also be extended to other comparable ecosystems, such as oyster reefs, to address their stability under climate change, thereby informing strategic management.