Researchers have discovered crucial connections between coral populations at different depths using blushing coral star and genomic DNA analyses. They found four unique genetic lineages, revealing strong genetic ties between shallow and mesophotic (mid-depth) coral populations. Shallow-specific lineages were identified as having lower genetic diversity and increased inbreeding compared to more depth-generalist lineages. Notably, mesophotic reefs have been identified as essential reproductive sources, especially in the Lower and Upper Keys. Corals from these deeper areas have significant potential to help revitalize and restore the diminishing shallow reefs in the Florida Keys National Marine Sanctuary.
Since the 1970s, coral reefs within the Florida Keys National Marine Sanctuary (FKNMS) have faced severe declines, including a staggering 50% reduction in coral cover from 1998 to 2011. While the FKNMS coral reefs have undergone extensive research, studies focusing on the mesophotic zone—ranging from about 100 to 500 feet deep—have been comparatively limited.
Due to their depth and relative isolation from shore, mesophotic coral ecosystems might better endure anthropogenic stressors. They may also serve as safe havens for depth-generalist coral species, supplying viable larvae to restore degraded shallow reefs after occasional disturbances. In the FKNMS, mesophotic corals have mostly escaped the damage associated with bleaching and stony coral tissue loss disease, making them a potential key source of genetic diversity for shallow reefs in the area.
Using the blushing coral star (Stephanocoenia intersepta), commonly found throughout the Western Atlantic, a team of researchers from Florida Atlantic University’s Harbor Branch Oceanographic Institute examined the relationships among coral populations at varying depths and locations. They utilized genomic DNA analyses to assess genetic diversity, genetic differences, and connectivity among populations of blushing coral star and their symbiotic algal partners through SNP genotyping and ITS2 sequencing.
“The blushing star coral has a broad range in depth and geography, making it an excellent species to study how populations are linked across various depths and locations,” stated Ryan Eckert, the first author and a Ph.D. candidate at FAU Harbor Branch. “While less common on shallow reefs throughout their range, they are more prevalent and cover larger areas in the mesophotic zone.”
Findings from the study, published in the journal Heredity and highlighted on the cover, identified four distinct genetic lineages of the blushing star coral. The research showed strong genetic connectivity between shallow and mesophotic populations from the two main lineages sampled. The shallow-specific lineages demonstrated lower genetic diversity and increased inbreeding compared to the depth-generalist lineages. Furthermore, the analysis pointed out that mesophotic reefs serve as critical reproductive sources, particularly in the Lower and Upper Keys.
“Corals from deeper mesophotic regions possess significant potential to aid in the restoration and replenishment of the declining shallow reefs in the Florida Keys National Marine Sanctuary,” remarked Joshua Voss, Ph.D., the senior author, principal investigator of the study, and an associate research professor at FAU Harbor Branch. “Additionally, vital expansions in the ‘FKNMS Restoration Blueprint’ include further protections for mesophotic corals across the Keys. Given that coral cover in the region has been on the decline since the 1970s, these findings, along with new management advancements, provide hopeful opportunities for some recovery of the coral reefs.”
Eckert expressed concern regarding the reduced diversity and higher levels of inbreeding among the shallow specific lineages, which may pose risks for future conservation and restoration efforts.
“However, even if these deeper corals cannot directly repopulate shallow reefs with viable larvae in the future, they could still be valuable for establishing a ‘seed bank’ or for rescue and breeding programs within land-based nurseries to facilitate current and future restoration initiatives,” Eckert noted.
The distinct cryptic lineages of the blushing star coral, with minimal mixing despite their geographical overlap, suggest some degree of reproductive isolation. This isolation could arise from factors such as varying spawning schedules or high inbreeding rates stemming from localized fertilization. Additionally, larval behavioral traits and settlement preferences might influence these patterns, contributing to the reduced genetic diversity observed in shallow populations of the blushing coral star.
“By identifying and characterizing the genetic diversity across various coral lineages, we can enhance our management and protection strategies for coral populations, especially as we confront ongoing and future environmental challenges,” explained Voss. “This strategy will ensure that coral conservation and restoration efforts are based on a more thorough understanding of genetic diversity, which is crucial for sustaining the resilience and vitality of our coral reef ecosystems.”
The co-authors of this study included Alexis Sturm, Ph.D.; Ashley Carreiro, research laboratory manager; and Allison Klein, a Ph.D. candidate—all affiliated with the Voss Laboratory at FAU Harbor Branch.
This research was supported by NOAA Ocean Exploration and Research, awarded to Voss (NA14OAR4320260) through the Cooperative Institute for Ocean Exploration, Research, and Technology, alongside funding from the NOAA National Center for Coastal Ocean Science (NA18NOS4780166) awarded to Voss and S. Herrera, through the Connectivity of Coral Ecosystems in the Northwest Gulf of Mexico project.
