Facilitative interspecific interactions in marine vertebrates across scales: from individuals to ecosystems.

Facilitative interspecific interactions (FIIs) confer benefits to at least one participant without detriment to others. Although often less emphasised than antagonistic interactions in ecological studies, this review highlights the significant ecological role of FIIs across biological scales - from individual behaviours to population, community, and ecosystem-level effects - with a focus on mobile marine vertebrates such as birds, mammals, and fish. These interactions enhance foraging success, shape predator-prey dynamics and contribute to the structure and function of marine ecosystems. FIIs include diverse associations such as multi-species aggregations among marine apex predators (e.g. dolphins, seabirds, and surface-feeding fish), mixed-species shoals, fish cleaning mutualisms, and cooperative foraging involving predators, including humans. At the population level, FIIs can improve survival and fitness, impacting the life histories and population dynamics of marine apex predators, with some species exhibiting a clear dependence on heterospecific facilitation. Despite recent advances, gaps remain in our understanding of how FIIs scale up to influence marine communities and ecosystem processes, limiting their integration into management tools. Ecosystem models - often used to inform management decisions - typically focus on principles of resource flow and species interactions driven by predation and competition, often overlooking facilitation. Integrating FIIs into ecosystem modelling could enhance Ecosystem-Based Fisheries Management, particularly for conserving vulnerable apex predators that may rely on facilitative interactions. Furthermore, FIIs involving humans and apex predators offer unique opportunities for data collection and model development, improving our understanding of the broader impacts of FII in marine environments, from individual behaviours to ecosystem functioning.