Determining primary contributor to high chlorophyll a production and the effects of CO2 seeps at a volcanic Caribbean reef site

Ocean acidification, driven by the absorption of anthropogenic and natural carbon dioxide (CO2) at the sea surface, has decreased the average ocean surface pH from 8.21 to 8.10 since preindustrial times. This shift leads to consequences in an ecosystem’s food web, biodiversity, and stability as calcifying organisms are most vulnerable to these changes in acidity. This study investigated the effects of CO2 enrichment on overall pH and chlorophyll (Chl) concentration at Bubble Beach, a Caribbean reef site containing a natural CO2 seep. Water quality and biological data was collected across six reef sites in St. Croix, Anguilla, and Dominica to assess the effects of acidification on pH and its relationship with Chl concentrations. Omnibus and post-hoc analysis were employed to determine the correlation between photosynthetic activity of non-calcifying organisms and elevated Chl concentrations in conditions of depressed pH due to the presence of a CO2 seep. Results indicate this addition of CO2 at Bubble Beach did not contribute substantially to an increase in acidic conditions relative to the five other Caribbean reef sites. Focus shifted to analyzing the primary contributor of high Chl concentrations at Bubble Beach, determining whether a notable abundance of non-calcifying organisms when compared to other sites was present. These findings indicate no significant difference in hard or soft-bodied organism cover at this site, warranting further investigation into what factor is truly influencing such a high Chl concentration. The SEA Coral Reef Conservation: Caribbean program plans to return to Dominica each year to build a time series of this reef site, as questions still remain regarding the buffered effects of a CO2 addition on pH, as well as high Chl concentrations with no significant benthic cover in comparison to other Caribbean reef sites.

SEA Coral Reef Conservation: Caribbean 

Sea Education Association (SEA) is a global learning and research community where students spend 2-6 weeks aboard one of their 134-foot vessels, sailing to numerous locations around the world. Programs are offered short-term (summer) and semester-long, with the first half spent in Woods Hole, MA on the SEA campus and the second aboard the SSV Corwith Cramer or SSV Robert C Seamans. These programs offer an interdisciplinary approach to addressing critical environmental issues through the exploration, understanding and stewardship of marine and maritime environments. 

The SEA Coral Reef Conservation: Caribbean 2024 program sailed to three islands: St. Croix, Anguilla, and Dominica. In the Caribbean, students conducted standardized reef survey techniques, such as roving diver surveys and photoquadrat analysis, and collected comparative data on reef health, with the deployment of a HydroCAT sensor. I contacted the chief scientist of the Coral Reef Conservation: Caribbean program, Dr. Heather Page, in the spring of 2025 to inquire about research opportunities, as we share similar interests regarding both coral reef ecology and ocean acidification. I was given the opportunity to analyze data collected on previous SEA Caribbean programs, where I then developed a research project focused on the Bubble Beach, Dominica reef site using data collected from 2024. This project has been an ongoing internship with Dr. Page and Dr. Gravinese (Eckerd sponsor) with the expected outcome of a poster presentation at the 2026 Eckerd Spring Symposium. Dr. Page plans to return to Dominica each year with the SEA Coral Reef Conservation: Caribbean program to develop a time series for this island. Even though my current project is primarily data analysis, I hope to have the opportunity to continue this research and possibly contribute to the data collection aspect of this ongoing project in the future.

For more information:  kjthomas@eckerd.edu