Peering into the twilight: a systematic review on visual-based investigation of worldwide mesophotic ecosystems

Mesophotic ecosystems host high biodiversity and support a vast variety of habitats. Owing to climate change, there is a growing interest in the study of mesophotic assemblages as a possible pocket of biodiversity for species. However, due to logistic constraints, these habitats have been historically less investigated and mostly neglected in conservation planning. Thus, it is difficult to gain a global overview of the state of the art, especially with regards to sampling methodology. Here, we conducted a systematic literature review, extracting data from 1001 publications on mesophotic research at a global level, focusing on visual-based methodologies, to identify gaps, emerging trends, and to supply useful information to improve sampling methodologies of mesophotic ecosystems and their reporting. Overall, the review highlighted an evidently uneven spatial distribution and a bias towards some taxonomic groups, i.e., corals and algae. From a methodological perspective, it showed that most studies at community level were performed with no standardized protocols. Even if crucial for the understanding of the functioning of these ecosystems, baseline data and long-term monitoring projects are virtually lacking. Despite these challenges, this review clearly shows a surge in interest and research effort driven by technological development. Considering the previously underestimated vulnerability of mesophotic ecosystems to anthropogenic pressures and the current climate change scenario, there is a pushing need to study mesophotic ecosystems through a standardized framework to adequately inform conservation and restoration measures. © 2026 The Authors