GSA Connects 2021 in Portland, Oregon

Paper No. 91-12
Presentation Time: 9:00 AM-1:00 PM


GREER, Lisa1, WIRTH, Karl2, JOHNSON, Ginny1, JONTZ, Jordan1, NGUYEN, Alicia1, PETSINGER, Lillian1 and CURRAN, H. Allen3, (1)Geology Department, Washington and Lee University, Lexington, VA 24450, (2)Geology Department, Macalester College, Saint Paul, MN 55105, (3)Department of Geosciences, Smith College, Northampton, MA 01063

In the last few decades, Caribbean Acropora spp. coral colonies have faced collapse, with a loss of up to 98% of acroporids. A variety of environmental stressors, including climate change, overfishing, and white band disease have contributed to the decline in live coral cover across the Caribbean. However, Coral Gardens, Ambergris Caye, Belize has been documented as an ecological refugium, in which acroporid coral cover has remained much higher than at other reefs in the region. Our goal was to assess the current state of Acropora cervicornis at Coral Gardens. We compared the percentage of live coral cover in December of 2020 and June of 2021 to data from prior years beginning in 2012. We photographed and analyzed a total of 141 1-m2 quadrats across 5 previously established transects on the reef. Images were rectified using Matlab and live coral cover was outlined in each quadrat using Adobe Illustrator. We then used a Matlab script to calculate the percentage of pixels representing live coral within each photograph. These percentages were compared to similar data from each year since 2012, excluding 2015 (no data). Between June 2014 and October 2016, mean live A. cervicornis at Transect 5 declined from 51.7% to 19.2% and remained low through 2017 before increasing to 25.5% in 2019 and 26.8% in 2020. Transect 1 exhibited a similar decline, reaching a low of 6.4% in 2020. From 2020 to 2021, average live coral cover increased from 6.4% to 12.4% for Transect 1 and from 26.8% to 34.4% for Transect 5. Using t-tests, we determined that the difference between the average coral cover from 2020 to 2021 for both transects is statistically significant (p<0.001). The trend of increasing live coral from 2017-2020 continued through June 2021. This indicates that the acroporid colonies in this refugium remained healthy despite environmental stressors including rising temperatures and regional outbreaks of white band disease. Potential sources for coral resilience, including local conditions and possible genetic factors, are being explored. Against a backdrop of Caribbean-wide coral demise, the increasing coral cover at Coral Gardens makes it a compelling case study for understanding ‘reefs that work,’ which we hope will prove valuable for future reef conservation initiatives.