Cryptobenthic reef fishes may not be safe from invasive lionfish (Pterois spp. Oken, 1817).

Lionfish (Pterois spp.) are hypothesized to negatively influence cryptobenthic reef fish assemblages through predation. We evaluated these potential effects on Caribbean reefs in Costa Rica and tropical reefs in Brazil. Brazil provided a reference condition for cryptobenthic assemblages prior to lionfish invasion, while the Costa Rica sites enabled comparisons between reefs inside marine protected areas (MPAs), where lionfish removal did not occur for several years, and adjacent fished reefs where removals occurred. Visual censuses (30 m × 2 m transects, 0.5-4 m depth) were complemented by simplified assessments of reef structure and benthic cover. Cryptobenthic fish abundance was consistently higher in Brazil than in Costa Rica. Within Costa Rica, abundance was significantly lower inside MPAs, where higher lionfish densities were recorded, compared to adjacent fished reefs. This pattern indicates differences in cryptobenthic fish abundance across sites with contrasting lionfish presence. Our findings reinforce concerns that MPAs may inadvertently function as refuges for invasive species, highlighting the importance of adaptive management strategies, including targeted removals and monitoring, to mitigate ecological impacts and protect reef biodiversity.