Harnessing Coral Resilience through Nursery-to-Reef Restoration Processes

The summer of 2023 highlighted the need to scale up the production and diversity of boulder corals kept in coral nurseries through the identification and propagation of resistant and/or resilient coral species and genotypes to mitigate losses from future environmental disturbances. To this end, Colpophyllia natans and Diploria labyrinthiformis were collected from nearshore reefs in the upper, middle, and lower Florida Keys. Each coral was then sampled for microbiome and metabolome analysis, fragmented, and placed in FWC’s in-water coral nursery. Sampling was repeated after two months in the nursery to assess changes in the microbiome and metabolome due to translocation. While in the nursery, corals were monitored routinely to assess survival and note overall health. Survival analyses revealed genotype specific differences with the lowest survival observed in both species collected from West Turtle in the middle Florida Keys. Survival of C. natans was influenced by the size of coral collected, with larger corals exhibiting higher mortality. This was reflected in both linear regression analysis and survival curves. However, five of the six largest C. natans corals were collected from West Turtle, precluding the interpretation of this relationship due to interaction effects and unknown confounding factors. Coral size did not have a significant effect on survival trends of D. labyrinthiformis. 

Microbiome analysis identified similar microbial communities in C. natans and D. labyrinthiformis that did not vary greatly over time or across collection locations, and less than 2% of the variation in microbial communities was explained by coral species or timepoint. Microbial community differences were influenced primarily by coral specimen, and 23% of the community variation was explained by the interaction between genotype and sampling timepoint. Changes in specific microbial families due to translocation were detected, with generally decreasing ammoniaoxidizing archaea and increasing anaerobes observed in nursery corals.

Similar trends resulted from metabolome analysis of C. natans and D. labyrinthiformis and indicated a shift in the metabolome over time and after translocation, with less variability between the metabolomes of corals collected across the upper, middle and lower Florida Keys relative to propagated corals after two months in the nursery. This was also reflected in Shannon diversity indices where statistically significant differences in metabolomes between both species and timepoint were observed. Metabolome diversity was greater in D. labyrinthiformis than C. natans, and increased diversity was found in nursery corals than the wild collected colonies.

Analyses are ongoing to identify specific biological pathways perturbed by the translocation of these species to an in-water nursery. Preliminary findings suggest a distinct change in carnitine after translocation. PCAs showed significant location-based differences in metabolomes for both species. Corals collected from Pickles Patch had unique metabolome communities relative to West Turtle and Looe, but after two months in the nursery changes in the metabolome of West Turtle corals differed from corals originating from the other sites. This shift in the metabolome of West Turtle corals combined with the higher mortality observed in corals from this location suggest the potential role of metabolites in coral survival and warrant further investigation to determine their utility as predictors of health for selective coral propagation.

This study highlighted some of the challenges in identifying resilient corals for use in restoration while applying novel tools to investigate how coral propagation processes influence microbial and metabolite communities of two threatened stony coral species. These data may help us to better differentiate healthy coral genotypes from those with higher probability of mortality. However, further analysis into the role of specific microbes and metabolites in survival is needed, in addition to baseline data for other stony coral species used by practitioners, to evaluate the utility of these tools in improving restoration success.