Students Discover Massive Mortality

sea fan

The Common Sea Fan (Gorgonia ventalina) is undergoing an unexplained die-off along Belizean reefs. While snorkeling along the reefs in the Field Study in Belize class, it became obvious that the brown algae covering most of the sea fans was not a sign of natural coral health. Sara Smith (EcoBio, C‘14) and Sarah Delong (EcoBio, C‘13) studied this phenomenon for their class project by quantifying the algae cover of sea fans in two locations (South Water Caye and Tobacco Caye).

Healthy coral has a layer of mucus that sloughs off in the water and prevents algae and other harmful things from growing on the surface of the coral. When a colony of coral becomes covered with algae, that colony is no longer alive. Using this assumption, Smith and Delong found that there was indeed a very high mortality rate of Sea Fans in both locations studied. There are many diseases that can affect Sea Fans. Black and Red-Band Disease, as well as Aspergillosis are all pathogens that have caused die-offs in the past. While Smith and Delong were able to determine the number of dead corals, there was no way to determine what actually caused the deaths. However, mortality on such a large scale is abnormal for the population and is a troubling phenomenon in an already precarious ecosystem. It has been shown that corals stressed by other environmental changes can become more vulnerable to pathogens that the population would otherwise be able to withstand. In spite of the die-off, a number of fans appear to be unaffected. These individuals may indicate that the Sea Fan population could recover from this setback. The data collected during the Field Study In Belize can be used as a baseline for future evaluation of Sea Fan population health.

“Field Studies in Belize” is a 10-day intensive immersion course in which Sewanee students study coral reef and rainforest ecosystems at two separate field stations in Belize. The course is led by Professor Jon Evans of the Biology Department and assisted by Jordan Casey (EcoBio, C’09) who is currently a Ph.D. student in marine ecology at Cook University in Australia. This year, 10 students participated in the program from May 29 – June 9. After extensive exploration and natural history study, students conduct a research project at each site. This year at the BFREE rainforest field station, students studied bird distribution along a tropical river, land snail diversity, and the population structure of two rainforest tree species. At South Water Caye on the Belizean Barrier Reef, students examined the territorial behavior of different damselfish species and the association of goby cleaner fish with different coral species, and documented the mass mortality event in sea fans reported above.