A framework for identifying and characterising coral reef "oases" against a backdrop of degradation

Human activities have led to widespread coral reef decline; however, the severity of degradation is spatially heterogeneous due to some locations resisting, escaping, or recovering following disturbances. It is imperative to... [ view full abstract ]

Human activities have led to widespread coral reef decline; however, the severity of degradation is spatially heterogeneous due to some locations resisting, escaping, or recovering following disturbances. It is imperative to develop frameworks for identifying and characterising locations that have not degraded to the same extent as their neighbours (“oases”), as they may have considerable conservation value. Here we present such a framework to identify coral reefs using publically available time-series data on coral cover. We calculated standardised coral cover (z-scores) to distinguish sites that deviated positively from annualized regional mean coral cover, and used the coefficient of variation (CV) of coral cover to assess how these potential oases varied temporally. We first illustrate our z-score approach within a modelling framework by extracting z-scores and CVs from simulated data on coral cover, we then apply the approach to time-series data from long-term reef monitoring programs in four focal locations in the Pacific and western Atlantic. Among the 123 sites analysed, 40 had positive z-scores for median coral cover and were categorised as oases. Of these, 32 (80%) were temporally stable as defined by a CV ≤ 50%. Only two sites (5%) recovered from disturbances by increasing coral cover. Our results demonstrate that escaping or resisting disturbances is more common on reefs than recovery over the last few decades. Finally, we found that standardised coral cover was positively associated with coral community calcification capacity, suggesting that our approach identified oases that are exceptional in at least one aspect of ecological function.