Small-scale mapping of indeterminate arborescent acroporid coral (Acropora cervicornis) patches

Western Atlantic populations of the staghorn coral Acropora cervicornis have drastically declined over the past few decades. Hence, interest in its ecology and spatial extent has increased. Acroporid corals with indeterminate arborescent growth like A. cervicornis primarily reproduce asexually by fragmentation, which can lead to extensive monotypic patches. Since fragmentation is a major component in indeterminate acroporid reproduction, these patches may expand or move over time. Periodic perimeter mapping facilitates comparison of patch areas to determine movement or expansion. A repeatable, low-cost method using a differential GPS carried by a snorkeler was employed to map the perimeter of A. cervicornis patches in southeast Florida. Perimeters were mapped over a 3-year period. Patch boundaries were dynamic, expanding in one or more directions. Patch areas increased by up to 7.5 times their original size and moved up to 51 m. Results were corroborated by spatial cluster analyses of in situ live coral cover measurements. Getis-Ord Gi* statistic and Anselin Local Moran's I spatial cluster analyses of live coral cover within an array of in situ monitoring plots indicated that significant high cover clusters moved in the direction of mapped patch perimeter expansion. Expansion was coupled by more than 50 % decreases in total live cover. Information gained herein shows that A. cervicornis patches are spatially and temporally dynamic, having implications to long-term permanent transect monitoring studies and framework development. Results may be applicable to other shallow water indeterminate arborescent acroporid coral species.