SPATIAL VARIATION AND THE SURVIVABILITY OF AN ACROPORA CERVICORNIS PATCH REEF IN BELIZE

Acropora cervicornis (staghorn coral), a branching shallow-marine coral, was once common on Caribbean reefs. A. cervicornis has been an important framework coral since the Pleistocene, but its population has declined dramatically since the 1980s. One location where an A. cervicornis-dominated reef still thrives is Coral Gardens, a patch reef located inshore of the Mesoamerican Barrier Reef in Belize. There are two sections of this patch reef, one larger and less viable and one smaller with greater live-coral cover. Physical and environmental variations across the reef may have influenced the smaller patch’s resilience. This study looks at heterogeneity of live coral abundance, grazer populations and growth patterns across the two patches of Coral Gardens to determine why the smaller patch is thriving more than the larger patch. To assess spatial heterogeneity, live coral, density of live branch tips, and orientation of live branches were assessed using photographic data from 131 m² quadrats along five Coral Gardens transects. Transects 1-4 (T1-4) were located on the main body of the reef and Transect 5 (T5) was located on a smaller, isolated patch of A. cervicornis ~36 m southeast of the main patch. Adobe Illustrator and MATLAB were used to manually trace live coral as well as quantify directional growth of individual coral branches in each quadrat. Stationary visual fish and urchin counts of each quadrat were used to characterize variation in grazer community dynamics between T1-4 and T5. These data suggest that T5 is distinctly different from the main body of Coral Gardens. T5 contained an average of 56% live coral cover per m², whereas quadrats along T1-4 averaged 32, 23, 25 and 19% live coral per m², respectively. More stoplight and striped parrotfish and significantly fewer urchins (0.1 per m²) were found at T5 compared to T1-4 where there was an average of 39.5, 14, 20 and 24 urchins per m², respectively, further indicating dissimilar grazer community dynamics between the two reef sections. Rose diagrams of branch growth direction on T5 showed that most branches favor growth westward, away from the reef crest, but branches on T1-4 have little to no directional trend. Whether or not heterogeneity across Coral Gardens is from hydrologic factors, genetic variation, or both is unclear; these ideas are being explored.