Award: OCE-2019992

This project focused on long-term changes on coral reefs in the coastal waters of the United States along the shores of St. John, US Virgin Islands, and within the Virgin Islands National Park. This location has a long history of scientific investigation extending to 1956, with the current project running from 1987-present. The last six years have extended the project to one of the longest running studies focused on the coral reefs of the Caribbean, with this record covering 40 years with annual resolution. The award leveraged the archived scientific history of these reefs to ask important questions pertaining to the health of US coral reefs and to provide a scientific training ground in which the American STEM workforce could be developed. The research sought to describe the mechanisms causing coral abundance to decline to unprecedented levels and to determine whether these reefs have stabilized in their degraded state, are sliding inexorably to extinction, or whether there remains the potential for recovery.

The research was based at California State University, Northridge, from which expeditions of America students and educators led by the PI (Edmunds) departed for month-long programs to St. John. The summer research was based at the Virgin Islands Environmental Research Station that is owned by the University of the Virgin Islands, and each day the team worked from small boats using scuba and snorkel to sample the reefs to 60 ft depth. The reefs were described through detailed counts of corals, algae, and invertebrates, with photographs providing a resource amounting to 13,000+ images over 41 years. The reports generated from these data support the Intellectual Merits of this study and provide unique insights into the state of US coral reefs as well as those throughout the Caribbean. One of the most valuable products from this award is the archive of data and photographs in the public domain that provides a “time machine” through which changes in the reefs can be viewed and from which further research and educational projects can be launched.

The project generated over thirty publications in which the most significant discoveries make six key contributions. First, 40-years of photographs has supported a comprehensive analysis of the cause of coral death, thus highlighting the importance of chronically increasing seawater temperature in driving ecosystem collapse. Second, although coral cover has remained ≤ 4% on many reefs for > 32 years, it is striking that none of these reefs have degraded to a complete absence of coral. This may indicate that these reefs are now locked in a stable state of low coral cover from which recovery remains feasible. Third, detection of unprecedented mortality of the fire coral Millepora over 2024/25 caused by high seawater temperature (to 87°F) has created a graveyard of dead corals over > 43 km of coastline. Previously, this coral has appeared resistant to disturbances, and its widespread death represents a loss of one of the last few corals remaining at high abundances. Fourth, we have identified the yellow mustard hill coral (Porites astreoides) as a potential “winner” on these degraded reefs and have shown that its success is associated with the production of larvae without the fertilization of eggs with sperm (i.e., through parthenogenesis), and which tend to be retained in the local habitat. Fifth, the elegance of a half-century-long study allowed us to capture the second mass mortality of the important long-spined Caribbean sea urchin (Diadema antillarum), which has further spurred the growth of algae and made it more difficult for corals to grow. Finally, we have completed a synthetic study of the results of coral reef monitoring throughout the Virgin Islands over 31 years at 35 sites. The results demonstrate that declining abundances of corals is preferentially affecting species that release their gametes into the seawater, thus favoring corals that brood their larvae. This profound change in dominant reproductive strategy is leaving reefs depleted of coral, yet preferentially populated by brooding species that are unlikely to build future reefs as wave resistant platforms.

Broader Outreach activities have remained at the core of this project and we have focused on exposing American children and educators to hands-on marine biology experiences, contemporary scientific discoveries, inspiring personal journeys in science, and the natural world outside of on-line ecosystems. These outcomes have been achieved through in-person marine biology clubs at local schools in California, a “library program” of aquaria and marine organisms we host for temporary visits to local schools, and by embedding California educators in field expeditions to St. John. These experiences are baked into a program that develops the American STEM workforce to the MS degree level (and beyond) and creates globally aware, scientifically informed, and practically experienced young scientists capable of addressing the grand biological challenges of the 21^st Century.

Last Modified: 10/02/2026
Modified by: Peter J Edmunds