Restoration success limited by poor long‐term survival after 9 years of Acropora cervicornis outplanting in the upper Florida Keys, United States

Abstract

The degradation of coral reefs has resulted in the expansion of coral reef restoration projects worldwide. In the tropical western Atlantic, most restoration efforts focus on outplanting Acropora cervicornis, once a dominant reef‐building branching coral, now found predominantly in spatially isolated populations. Hundreds of thousands of A. cervicornis colonies are outplanted onto degraded reefs every year; however, long‐term growth and survival data of outplanted corals is limited. In this study, we assessed the long‐term restoration of A. cervicornis by determining the relationship between surviving outplant populations and restoration effort. We surveyed coral populations at 11 sites in the upper Florida Keys that represented a gradient of restoration effort, defined by the total number of outplants, number of outplanting years, and time since last outplanting. We found a negative relationship between the amount of A. cervicornis live tissue and time since last outplanting, suggesting that outplants are not surviving longer than 2 years. In addition to restoration effort, we investigated how past and present benthic community metrics such as coral density and diversity may influence long‐term outplant survival. We found a positive relationship between the amount of live A. cervicornis tissue and pre‐restoration coral density, suggesting that areas that previously supported dense populations of corals may facilitate restoration success. Ultimately, this study finds that restored A. cervicornis populations decline over time, and continued outplanting effort is needed for the persistence of the species in certain areas. This study also highlights the need for more long‐term monitoring to inform adaptive management and restoration strategies.