Immune gene expression as a biomarker for predicting restoration success in the branching coral Acropora cervicornis 

Background As coral reefs continue to decline across the globe there has been a rise in coral restoration efforts where a diversity of genets of different coral species are outplanted from nursery-grown stocks onto different reef sites to restore ecosystem structure and function. However, previous work has found highly variable growth and survival among genets and reef sites, making it difficult to predict restoration outcome based on coral genotype alone. Identification of a dynamic biomarker would allow restoration practitioners to assess the health of a coral prior to outplanting, which could enhance restoration efficacy by facilitating selection of individuals in top condition for restoration cohorts. Results Genets of Acropora cervicornis, which ultimately exhibited low restoration value (poor growth and survival outcomes), upregulated key immune genes in the nursery prior to outplanting on nine different reef sites in the lower Florida Keys in 2018. These immune genes remained upregulated and differentially expressed among genets after exposure to different sites for 12 months. When the same ten coral genets were again outplanted to a subset of two focal reef sites in 2022, genet survival rankings shifted, with some of the lowest surviving genets from 2018 ranking as high survivors in 2022, and vice versa. When measured in the 2018 outplant, no clear correlation between microbial community composition and restoration value was found. Conclusions Elevated immune expression prior to and during outplanting indicates that a potential immunocompromised health state can impact future performance. Changes in survival rankings of the same genets between 2018 and 2022 indicate that performance is dynamic and may be determined by immune state, rather than a genetically fixed trait.