Beyond single drivers: A multi-stressor framework for understanding and managing jellyfish proliferation under concurrent anthropogenic and climate pressures

The Mediterranean Basin is a biodiversity hotspot increasingly threatened by anthropogenic pressures, such as coastalization, overfishing, and climate change. These stressors may contribute to jellyfish blooms, which jeopardize marine ecosystems and the services they provide. Yet, their combined effects remain poorly understood. This study models the responses of two jellyfish with contrasting thermal preferences, Rhizostoma pulmo and Aurelia spp., to global changes occurring in the Western Mediterranean Sea between 2004 and 2020. The loop analysis method was used to assess the combined effects of multiple anthropogenic pressures on the abundance of jellyfish and the model outputs were compared with the observed dynamics of both jellyfish. Results suggest that global change favored R. pulmo proliferation during the study period, whereas Aurelia spp. abundance did not show much change. The effects of different fishing effort scenarios on jellyfish blooms were also modeled to provide Western Mediterranean stakeholders with keys to remediation. While increased fishing effort in a context of global change is expected to foster jellyfish proliferation, reducing fishing pressure alone is unlikely to curb their abundance, because of the influence of concurrent antagonistic drivers. Our results highlight the multifactorial nature of jellyfish blooms and the need for integrated approaches to mitigate their proliferation. This study contributes to the objectives of the EU's Marine Strategy Framework Directive by improving the understanding of jellyfish as indicators of ecosystem imbalance and informing ecosystem-based management strategies.