Date of Award
2026
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
Department
Biological Sciences
First Advisor
Carlos Prada
Abstract
Motivated by the Deepwater Horizon oil spill chapters one and two focus on octocoral propagation techniques and coral settlement, respectively, in the mesophotic Gulf of Mexico along the Mississippi-Alabama shelf. In this area octocorals are common, large structure-forming organisms, and were among the most impacted. Restoring octocorals to oil affected sites and understanding settlement patterns may support community recovery. Chapter 3 investigates Caribbean wide population structure and hierarchy across distance and depth in a common octocoral, Eunicea flexuosa, results have implications for ecological speciation, conservation, and management of sessile marine populations. Chapter 1demonstrates the feasibility of ex-situ fragmentation as a coral propagation method in the mesophotic. Three species that were injured by the spill were tested -- Swiftia exserta, Thesea nivea, and Muricea pendula. After 500 days survivorship varied by species, fragment size, and deployment substratum. Large (³ 8 cm) fragments on hard substrate had higher survival rates (82%). S. exserta had the highest survival rate (89%) and an average growth of 2.1 cm year-1 ± 0.5 SEM. All species were robust to fragmentation, with minimal mortality observed at 53 and 143 days. Chapter 2 quantified mesophotic recruitment patterns through deployment of settlement arrays to two benthic substrates (rocky or sand), each with tiles of varied orientations and composition (limestone or concrete coated in limestone rubble). After 724 days a total of 100 coral recruits (92 scleractinian, 8 octocoral) were found, a recruitment rate of 4.7 corals m-2 y-1 (4.3 scleractinians m-2 y-1, 0.4 octocorals m-2 y-1). All three factors significantly influenced recruitment. The highest recruitment rates were on the top surface of horizontal limestone tiles placed over contiguous rocky substrate (13.0 corals m-2 y-1). These surface types should be prioritized when building artificial reef substrate for these environments. The higher recruitment of scleractinians compared to octocorals was at odds with ROV observations at the site with octocorals far more abundant than scleractinian colonies. This discrepancy highlights the need for further investigation into the population and recruitment dynamics structuring these communities. Our findings suggest that at mesophotic sites impacted by natural and/or anthropogenic disturbance, passive recovery may be insufficient, and active propagation techniques (from chapter 1) may be required to accelerate restoration. In Chapter 3, 234 E. flexuosa individuals from eight locations and multiple depths were sampled and genome wide variation analyzed through a ddRAD approach. Consensus-based analyses consistently identified two cryptic lineages associated with depth as the main driver of population structure. Geographic isolation had little support, though the shallow lineage exhibited significant isolation by geographic distance, while the deep shows a pattern of a large panmictic metapopulation. These results confirm that depth-segregated lineages in E. flexuosa are a Caribbean-wide phenomenon rather than a local pattern. Findings underscore the importance of recognizing cryptic lineages in management and restoration, as transplanting individuals across depths without regard for lineage identity risks reduced survivorship and degradation of source populations. Future work integrating environmental data with genomic patterns will be essential for understanding the selective mechanisms driving ecological speciation in this system and for predicting lineage distributions across the Caribbean.
Recommended Citation
Girard, John F., "CARIBBEAN POPULATION STRUCTURE OF EUNICEA FLEXUOSA AND MESOPHOTIC OCTOCORAL RESTORATION IN THE GULF OF MEXICO" (2026). Open Access Dissertations. Paper 4582.
https://digitalcommons.uri.edu/oa_diss/4582