Are visual surveys outdated? A case study comparing visual surveys designed for sun coral assessment and emerging 3D...

Biological invasions in marine systems pose significant challenges, requiring early detection and effective management for successful eradication. Tubastraea coccinea (Lesson, 1830), a highly invasive scleractinian coral, has successfully expanded in the Western Atlantic. These corals exhibit a strong preference for fine-scale geomorphological features, such as caves, crevices, and the undersides of large boulders on rocky reefs. However, the role of these features in the invasion dynamics of T. coccinea remains unclear. The present study validates a newly developed visual assessment protocol for quantifying these fine-scale rocky reef geomorphological features using structure-from-motion (SfM) photogrammetry. Our findings show no significant observer bias between different observers and SfM estimates across study sites. Furthermore, the visual surveys conducted were approximately 90 times more time-efficient than the SfM technique, demonstrating the practical implementation of this protocol for reliable quantification of fine-scale geomorphological features. The successful application of this protocol has the potential to aid in identifying high-risk invasion areas and inform effective management of T. coccinea.