Tractable field metrics for restoration and recovery monitoring of staghorn coral Acropora cervicornis

摘要

The staghorn coral Acropora cervicornis is a branching coral with complex morphology. While this structural complexity confers high ecological and habitat value, it hinders accurate quantification. An appropriate and quantitative coral 'unit' is required to effectively implement protective provisions (e.g. prevention of take or strategies to meet quantitative recovery criteria) for A. cervicornis under the United States Endangered Species Act. Actual measurements of 3-dimensional structure or extent of branches within colonies are time-consuming and therefore not feasible for monitoring application. This study calibrated arduous in-water measurements of total linear extent (TLE, sum of all branch lengths in a fully live colony, intuitively representing the 'amount' of coral in an individual colony) to more manageable standard field measurements of colony dimensions or photographs. The robustness of this relationship was then evaluated among colonies of different origin (wild, nursery-reared, transplanted) and different habitats (patch reef, shallow forereef, deep forereef) in the upper Florida Keys, USA. Within this sample set, colony volume (calculated as an ellipsoid based on 3 colony dimensions) was highly predictive of TLE (r~2 = 0.94 for log-log linear regression), and this relationship was consistent for colonies from different origins and different reef habitats. Thus, 'unit' coral abundance at the colony scale in terms of branch extent (TLE) can be reliably estimated from simple colony dimensions in the Florida Keys. Additional data are required to determine if different calibrations are needed in other populations, to adjust estimates for partial mortality of colonies, and to 'scale up' reliable estimates to thicket-or reef-scale.