Global Conservation Potential in Coral Reef Halos: Consistency over Space, Time, and Ecosystems Worldwide

AbstractHalos around coral reefs are landscape-scale patterns arising from multispecies interactions that collectively structure reefscapes over many thousands of square kilometers. First described in the 1960s, halos are known from a handful of locations and continue to captivate scientists. What remains unknown is how globally widespread, persistent, and dynamic halos are. We examined satellite imagery of reefs globally, coupled with in situ field observations, to show that halos are a globally ubiquitous, persistent, yet dynamic ecological phenomenon spanning vastly different systems. We further document the previously undescribed presence of halos outside the tropics surrounding seagrass "reefs" and highlight the temporal scales over which coral reef halos change, merge, and persist. Specifically, we show that halos can change in size over relatively short temporal scales of months, despite persisting over decades. In doing so, we document patterns suggesting that additional biophysical mechanisms than previously assumed may shape halos. Understanding the full suite of mechanisms governing halo formation and maintenance may enable us to use them as proxies for species interactions. Given the global extent of halos, their role in affecting sedimentary carbon storage, and their relationship with marine reserve existence and maturity, they may ultimately serve as globally relevant indicators of coral reef ecosystem functioning and health.