Spatial and temporal patterns of Diadema antillarum populations in the Southeastern Reefs Marine Sanctuary after an epizootic event

Coral reefs are diverse ecosystems that are undergoing unprecedented changes globally and regionally. Since the 1980s, epizootic events in the Caribbean have led to the diminishment of some keystone species, such as the long-spined sea urchin Diadema antillarum. In 2022, a novel massive die-off event of D. antillarum was reported throughout the Caribbean. The impact of its previous mortality and the recent die-offs emphasize the importance of demographic information to discern population changes. This study provides a crucial baseline of the current spatial and temporal population patterns of D. antillarum in the Southeastern Reefs Marine Sanctuary (SAMAR) in the Dominican Republic and highlights the need for continued monitoring to assess demographic changes. According to our findings, the population structure of D. antillarum in SAMAR is heavily skewed towards smaller sizes and has an usually high proportion of juveniles, due to recent mortality. The overall average density of urchins in SAMAR was low (0.029/m²) and comparable to densities observed after the mortality in the 1980s in other regions. Densities and temporal trajectories differ at two different scales: locality and site. Spacing appears to be of significant influence, however other drivers likely also affect the densities.