The Secret Life of Deepwater Corals in the Gulf of Mexico

Researchers, through a project funded by the NOAA Restore Science Program, are exploring the connections between different coral communities that live in deepwater and low light (mesophotic) habitats in the Gulf of Mexico. These researchers are looking at the genes in four coral species to find out the family relationship between corals of the same species from different parts of the Gulf of Mexico. This information is then fed into computer models to estimate how far coral larvae are able to disperse. Knowing where the coral larvae that are sustaining a coral community are coming from informs the conservation of the communities and the other organisms that live in these habitats Given the depth of these coral, collecting the tissue samples needed for the genetic analysis is not easy. Using remotely operated vehicles on three separate expeditions to the Flower Garden Banks National Marine Sanctuary, the researchers have taken over 700 samples (collected by non-lethal means) from the four coral species in depths ranging from 50 to over 2000 meters. Once the coral samples are back in the laboratory, DNA sequencing techniques are used to copy and compare the genes from each sample and determine how closely the coral are related.

A dense coral garden harboring octocorals, black corals, coralline algae, sponges, and cup corals, located at Elvers Bank at 117 m depth. Image credit: FGBNMS/UNCW-UVP

Preliminary conclusions from the genetic analysis and predictive computer models of one coral species (Callogorgia delta) have found that larvae of shallower coral (~400 meters deep) have larger horizontal dispersion patterns that are controlled by swirling water currents known as eddies. On the other hand, the larvae of corals from deeper regions (~800 meters) are impacted by water currents located near the bottom of the sea floor. The patterns of connection between populations can vary due to these currents which change seasonally. Another coral species (Paramuricea biscaya) showed a clear pattern of genetic differentiation by depth. Populations of this species found in deep sites (below 1700 meters) were genetically similar despite being separated horizontally by hundreds of miles. Populations sampled at shallower sites (between 1500 and 1300 meters) were more similar to each other than to the deep sites which were vertically only tens of miles away. The researchers have also learned from genetic analyses of Gulf coral that species of the genus Muricea have been misidentified, since 1990, as a species of Hypnogorgia.

The mesophotic habitats are home to both organisms unique to these depths and organisms found in shallower coral reefs. The same threats faced by the shallower coral reefs (pollution, overfishing, climate change, and invasive species, for example) can also threaten these little studied mesophotic reefs. Outside of marine sanctuaries, deepwater and mesophotic coral habitats are not protected leading to concern they may be damaged by such activities as trawling, or dragging the seafloor with heavy fishing gear, and oil and gas exploration. This research on mesophotic corals will produce maps of genetically connected corals and models of larval dispersal to guide management in the Gulf of Mexico. It can also be used to enhance our understanding of the Gulf of Mexico ecosystem and to help with restoration of degraded mesophotic and deepwater coral communities.

For more information, contact Santiago Herrera or Julien Lartigue.

Written by Pete Key