Differential disturbance effects and phenotypic plasticity among outplanted corals at patch and fore reef sites

Abstract

Practitioners have outplanted tens of thousands of nursery-reared coral colonies for restoration purposes, and interest in outplanting is increasing. However, restoration outcomes on natural reefs can be variable, and genotype- and site-specific differences have been reported. To systematically explore these differences, performance of restored corals was compared at two site types, and intraspecific variation in phenotype among six genotypes previously characterized in a nursery was simultaneously assessed. Nursery-reared Acropora cervicornis colonies were outplanted to geographically paired fore reef (n = 2) and patch reef (n = 2) sites. Colony growth and condition were monitored over one year. After the first monitoring visit, Hurricane Irma passed directly over outplant sites, providing an opportunity to examine disturbance effects across sites. In contrast to nursery results, growth did not vary among genotypes or sites either pre- or post-hurricane. Plasticity in pre-hurricane growth among sites was observed for one of the six genotypes examined. Stark differences in post-hurricane survival were observed between fore reef and patch reef sites: while 51.04 ± 9.38 % of outplanted colonies survived at patch reef sites, no colonies could be located at either fore reef site. Records from additional sites monitored by practitioners indicated higher outplant survival following hurricane disturbance at patch reef sites compared to fore reef sites. The lack of site or genotype effects on growth in A. cervicornis contrasts with a number of previous studies, however growth results were likely confounded by Hurricane Irma. Reduced structural complexity on Caribbean reefs may contribute to differential hurricane impacts between restored fore reefs and patch reefs. These results suggest that restoration practitioners should consider increasing effort on patch reef sites in restoration programs while also developing new strategies to foster resilience at fore reef sites.