Predator-mediated trophic connectivity between reef and oceanic habitats in Palau

Effective fisheries management and marine spatial planning depend on understanding how mobile predators link reef and oceanic ecosystems through cross-habitat movements and foraging. Predator resource use shapes movement and space-use strategies, providing insight into life history and behavioral variation, the identification of critical habitats, and spatial patterns of vulnerability to fishing and other human activities. Yet cross-habitat trophic connectivity remains poorly quantified in diverse coral reef and oceanic systems. Here, we used stable isotope (δ¹³C, δ¹⁵N) analysis, complemented by stomach content analysis, to examine cross-habitat resource use of predatory fishes across reef and near-reef oceanic ecosystems in Palau, in the Western Pacific, evaluating patterns across species, trophic guilds, and habitat associations. Cluster analyses, isotopic niche metrics, and Bayesian stable isotope mixing models revealed asymmetric but bidirectional connectivity, with resource utilization typically spanning both habitats but skewed towards reef or oceanic depending on species groups. Reef predators showed greater variability in resource use and higher reliance on oceanic inputs than oceanic predators relied on reef resources, with broad isotopic niches consistent with mobility, water-column use, and generalist foraging strategies. In contrast, most oceanic predators largely specialized on oceanic prey, although stomach contents documenting larval and juvenile reef fishes indicate occasional incorporation of reef-origin resources. Our results highlight the disproportionate importance of oceanic production in supporting reef predator populations, particularly where physical forcing concentrates prey near reef margins. Although reef contributions to oceanic predator diets were comparatively small, even limited inputs may be ecologically meaningful for migratory species during critical life stages. Together, these findings demonstrate widespread but trait-structured and individually variable predator-mediated connectivity that challenges binary "reef" versus "oceanic" classifications. Incorporating trophic connectivity into fisheries management and marine spatial planning can better align protection with the energetic pathways and habitat utilization sustaining predators in reef-ocean systems.