Video Transect-Based Coral Demographic Investigation

Abstract

Demographic studies that quantify species’ performances for survival, growth, and reproduction are powerful means to characterize sources of demographic bottlenecks and predict community dynamics. However, they require fine-scale surveys of populations in the field, and are often too effort-intensive to be replicable at a large scale and in the long term. We developed a standardized digital approach for extracting demographic data on species’ abundances, sizes, and positions within video transects, enabling back-from-the-field data acquisition and therefore optimizing time spent in the field. The approach is based on manual species identification, size measurements, and mapping in video transects, mimicking what is traditionally performed in the field, though it can be automated in the future with the deployment of artificial intelligence. We illustrate our approach using video surveys of a reef-building coral community in New Caledonia. The results characterize the composition of the coral community and demographic performances as key ecological indicators of coral reef health, shed light on species’ life strategies and constraints to their demographics, and open paths for further quantitative investigations. Key findings include the diversity of life strategies with contrasting levels of investment in survival, growth, and reproduction found among the six taxa dominating the coral community (Acropora, Montipora, Porites, Galaxea, Favia, Millepora), indicating the diversity of demographic paths to ecological success. Our results also indicate that several species have adapted mechanisms to prevail under limiting hydrodynamic environments through the propagation of coral fragments. Our approach facilitates image-based demographic investigations, supporting endeavors in ecology and ecosystem management.