Underwater robots map possible coral survivors off St. Croix

The Nature Conservancy and robotics company Aqua Satellite used autonomous underwater vehicles from October 26 through October 29 to photograph and map deep coral habitat along St. Croix's North Shore.

The survey focused on the mesophotic zone, roughly 100 to 500 feet below the surface, where divers have limited time and access. The five-foot robots linked high-definition imagery to location and depth data while onboard machine-learning tools classified parts of the seabed in real time.

Researchers reported preliminary signs of bleaching and mortality alongside areas with substantial living coral. TNC estimates that St. Croix lost about 90 percent of the living cover of elkhorn, staghorn and related acroporid corals during the 2023 bleaching event, so the team is looking for deeper survivors and locations that may offer cooler or otherwise more protective conditions.

The expedition is complete, but the findings are not. Researchers still must analyze the imagery and determine whether surviving colonies reflect heat-resilient genetics, local ocean conditions or other factors before selecting corals or sites for future restoration work.