The world’s coral reefs are under stress as ocean conditions vary over time (e.g., ocean warming, acidification, sediment and effluent runoff). In the past few years there have been even more dramatic changes to some Caribbean reefs due to the rapid spread of the highly contagious, deadly stony coral tissue loss disease (SCTLD).

Visually documenting reef conditions underpins our ability to assess disease and disturbance, detect change through time, and support science-based reef monitoring and management decisions. However, many underwater photogrammetry surveys rely on single-camera systems operated by individual divers, which severely limit the ability to capture large, contiguous reef areas, reducing the effectiveness of documenting spatial patterns of coral health, disease spread, and habitat complexity.

These and other limitations motivated the design and fabrication of the bespoke MantaRig, a multi-camera, multi-diver-operated underwater remote-sensing platform tethered to a surface GNSS, enabling repeatable whole-reef-scale image acquisition. The system consists of a 7.5-m-wide rig equipped with five cameras (GoPro HERO12) spaced 2 m apart, a cm-level-accurate GNSS receiver (Navisys GR-9029 RTK) supported by snorkelers, and SCUBA-deployed ground control points (GCPs) for geolocation of imagery.

Over three years of deployments off the western coast of Bonaire, we tested design and diver variants of field deployment and their impact on orthomosaic quality. We assessed maneuverability, personnel variations, how survey height influenced resolution and image clarity, how transect patterns (parallel vs. cross-grid) and end-of-transect maneuvers (pivot vs. translation) affected orthomosaic processing and quality (e.g., tie-point matching), whether diver-propelled versus scooter-assisted (LEFEET P1-XR) operation improved image quality, and how different surface GNSS configurations and GCP deployment strategies optimized geolocation accuracy.

The MantaRig substantially increases spatial coverage compared to single-camera approaches, while producing imagery suitable for generating high-resolution orthomosaic maps capable of resolving coral species and textural features. Regardless of the field deployment setup, we typically captured high-resolution data (~1cm) and spatial coverage with a typical along-track swath image width (at optimal 3-4-m heights above the reef) of ~12-15 m with ~80% forward overlap.

The MantaRig's modular frame is lightweight and easily disassembled for transport, yet robust and maneuverable underwater. By enabling the collection of contiguous, high-quality imagery over large reef areas, the platform enhances our ability to inventory and analyze complex spatial patterns, supporting monitoring and management of coral reef ecosystems.