Photogrammetry to monitor coral restoration in the USVI
The US Virgin Islands (USVI) Coral Innovation Hub, located on the island of St. Croix, is part of TNC’s Caribbean Coral Strategy with the overarching objective to Develop and deploy scalable solutions to improve coral reef health and maximize the benefits reefs provide to people and nature in a changing climate. The USVI Coral Innovation Hub includes a land-based coral nursery and research lab, as well as several in-water coral nurseries, where sexual and asexual coral propagation approaches are being applied and tested for large-scale coral restoration. With the goal of developing novel technologies and monitoring protocols to accurately and efficiently quantify the impacts of reef conservation efforts, the USVI Coral Innovation Hub is applying photogrammetric techniques to monitor coral restoration projects in the territory.
By sampling at time-points before, during, and after restoration activities, TNC coral scientists in the USVI are combining conventional reef monitoring surveys (e.g., Atlantic and Gulf Rapid Reed Assessment (AGRRA) diver surveys of benthos and fish) with standardized close proximity photogrammetric techniques (e.g., Structure-from-Motion) to regularly collect and analyze photomosaic and digital surface model products to monitor changes in coral restoration and control (unrestored) sites. The digital surface models generated from stereo photos, enable the monitoring of small changes in coral growth and loss at millimeter scale based on changes in the three-dimensional structure. With this information, TNC coral scientists can monitor changes in the reef, such as rugosity or structural complexity. These data are key for quantifying coral reef habitat restoration impacts in time and space, enabling comparison of changes to the reef structure in restored versus unrestored sites. Analysis of the effects of restoration on structural complexity and rugosity are especially pertinent for coral restoration projects that aim to maintain or enhance reefs for coastal protection and essential habitat for fishes and other reef-associated organisms.
In the USVI this monitoring approach and technology continues to be developed to meet the needs of different restoration projects. For example, the photo collection method has to be adapted to the parameters of a given site (shallow versus deep, transects versus plots) and algorithms are being iterated to derive the metrics that are most useful.