Mesophotic coral reef ecosystems (MCEs) support unique biodiversity and can act as refuges for species that also occur on heavily impacted shallow coral reefs. However, we still know relatively little about the physical and environmental structure of MCEs and the species that characterise them, especially within the Western Indian Ocean. To address this gap, we surveyed fish and macrobenthic assemblages between 10 and 100 m depth at three islands of the Comoros Archipelago using Baited Remote Underwater Video Systems (BRUVS). We also recorded temperature and photosynthetically active radiation (PAR) using a Conductivity–Temperature–Depth (CTD) probe. The structure of the fish assemblages was influenced by substrate type, relief and depth. More diverse fish assemblages were found on higher relief reefs, while low-diversity fish assemblages were associated with shallow sand and deeper low-relief sand/reef mosaic habitats. The reef fish assemblages delineated into three groups, corresponding to three depth zones: the photic zone (12–45 m), upper-mesophotic zone (45–62 m) and lower-mesophotic zone (63–98 m). The upper–lower mesophotic break aligned with the theoretical bottom of the euphotic zone at PAR1%surface. Macrobenthic assemblages comprised scleractinian corals on photic reefs, which transitioned at PAR3.5%surface to assemblages of non-light-dependent Octocorallia (soft corals and fans), Gorgonia (sea whips) and Antipatharia (black corals) on the mesophotic reefs. Scleractinian corals were found deeper in Comoros, which may confer greater resilience to climate change. The photic and lower-mesophotic reefs supported unique fish assemblages of depth specialist species, while the upper-mesophotic zone appeared to be a transition zone for fish assemblages. The presence of numerous large depth-generalist fishery species at depths > 50 m suggests that the mesophotic zone may be providing a depth refuge for fishery species that are overfished on shallow reefs. Our findings highlight potential resilience in the coral reef ecosystems of Comoros and illustrate the importance of mesophotic coral reefs in conservation planning.

The effective implementation of international, regional, and national commitments on marine biodiversity depends on reliable data. However, there is often a disconnect between the information generated by scientists and the data explicitly required by policy processes. This review systematically examined more than thirty policy instruments and mapped over 1,000 explicit data requirements to identify where science can most effectively contribute. Using the pressure–state–response framework, the analysis found that pressures such as pollution, fishing, and habitat degradation dominate policy demand, though important attributes such as intensity, frequency, and cumulative impacts are rarely specified. State-related data on species, habitats, and ecosystems are frequently required but remain difficult to monitor consistently due to technical, logistical, and conceptual challenges. Response-related data are less often highlighted in policy instruments but are increasingly needed to guide and evaluate management interventions, including spatial planning and restoration. Emerging priorities include climate-related stressors, connectivity, invasive species, blue carbon systems, and genetic diversity, which are not yet widely reflected in instruments but are growing in importance. The review concludes that improved monitoring resolution, better integration of pressures, states, and responses, investment in new technologies, and stronger interoperability and inclusivity are all critical. By clarifying points of convergence in policy demand and highlighting key gaps, the study provides practical guidance to help marine scientists and monitoring practitioners generate data that are more directly relevant to policy and governance.

Background During the 2022 Nekton Maldives Mission, we deployed a variety of platforms (snorkelling, remotely-operated vehicles and manned submersibles) to conduct video surveys of the biodiversity and composition of shallow (< 30 m), mesophotic (30-150 m) and deep-sea (> 150 m) benthos found in the Maldives’ central and southern atolls. In total, ~ 80 hrs of stereo-video footage were collected during the benthic transect surveys, which were subsequently processed using annotation software in order to evaluate benthic biodiversity and community composition. Here, we present a photographic guide for the visual, in situ identification of reef benthos encountered, including corals, sponges and other invertebrates that inhabit Maldives’ nearshore habitats. We hope that this identification guide will aid future imagery-based surveys or observations of organisms during fieldwork. New information A total of 283 morphotypes were identified, including those belonging to Octocorallia (61), Scleractinia (57), Porifera (38), Asteroidea (22), Antipatharia (15), Decapoda (13), Hydrozoa (12), Holothuroidea (10), Actiniaria (9), Echinoidea (8), Annelida (6), Chlorophyta (5), Gastropoda (4), Bivalvia (4), Ascidiacea (3), Crinoidea (3), Bryozoa (2), Cyanobacteria (2), Zoantharia (2), Cephalopoda (1), Ceriantharia (1), Corallimorpharia (1), Ctenophora (1), Ophiuroidea (1), Rhodophyta (1) and to an unknown category (1). Out of these, we identified 40 to species level, 120 to genus, 47 to family, 14 to order and suborder, 58 to class and subclass, two to phylum and one was of unknown phylum. This represents the first attempt to catalogue the mesophotic and deep-sea benthic megafaunal diversity in the Maldives using underwater imagery.