Unlike shallow-water corals, which are known for their symbiotic algae, there has been relatively little research on the feeding habits of deeper-water coral species. Deep corals are ‘heterotrophic,’ meaning they don’t make their own food. To grow these corals in the lab, you need to know what they eat in the wild. Before now, the diets of mesophotic corals impacted by the Deepwater Horizon oil spill in the Gulf of America (formerly the Gulf of Mexico) was unknown.
In an article published in the journal Invertebrate Biology, scientists from NOAA and the South Carolina Department of Natural Resources report on the natural diets of three species of mesophotic, or “middle light” corals: Swiftia exserta, Muricea pendula, and Thesea nivea. These species were injured by the 2010 Deepwater Horizon oil spill, and are now priority targets for restoration through the Mesophotic and Deep Benthic Communities (MDBC) Coral Propagation Technique Development Project, which is helping to restore coral ecosystems in the Gulf. The corals are collected from the seafloor using a remotely operated vehicle (ROV) and kept in aquaria at four different labs around the Gulf coast for the purposes of restoration, but their feeding has been a bit of guesswork.
The MDBC labs have successfully spawned these corals (which happened at the exact same time!). However, to keep the corals healthy and thriving in a lab setting, we need to know what they eat. To answer this question, NOAA and partners collected live corals from the wild. In the spring and fall of 2023 they conducted MDBC expeditions along the Mississippi-Alabama shelf. The team used ROVs to collect small samples from living corals on the seafloor from about 50-70 meters (~165-230 feet) deep. Once the samples returned to the surface, they were immediately frozen to preserve the tissue, and transported back to NOAA’s Hollings Marine Lab in Charleston, South Carolina.
In the lab, the team assessed the composition of fatty acids, which act as biomarkers that indicate what an animal has recently eaten. Different food sources contain characteristic fatty acid biomarkers, and the presence of these biomarkers in animal tissues can be used to determine what an animal is eating. What the authors found confirmed that deep sea corals are passively feeding on a variety of plankton, and the food sources switch depending on the season.
Although the proportions varied among species, all three had the same primary fatty acids. The fatty acid compositions suggest an omnivorous diet of zooplankton, phytoplankton, and other microscopic organisms. However, Muricea pendula had a different fatty acid profile than the other two species, possibly because its smaller polyps are limited to capturing smaller particles, which could indicate a greater reliance on phytoplankton. Interestingly, the diets for all three species varied between seasons. The variation suggests the corals eat phytoplankton in the spring, and in the fall they eat zooplankton. Since corals stay in one place on the seafloor, they rely on capturing the food around them–this seasonal change follows the trend of a springtime phytoplankton bloom in the Gulf, followed by a peak of zooplankton. Seasonal fatty acid fluctuation may also give insight into the reproductive cycles of the corals, since eggs and sperm are rich in specific fatty acids.
One common strategy for coral restoration has been to grow corals in the lab and then return them to the seafloor. This study unlocks an essential piece of the puzzle for maintaining mesophotic corals in the lab. Now, aquarists and scientists can better mimic what mesophotic corals eat in the wild, which helps keep corals healthy, growing, and well-fed. This in turn sets corals up for success when they are returned to the seafloor.
This work is part of the Coral Propagation Technique Development (CPT) project, one of four projects in the Mesophotic and Deep Benthic Communities (MDBC) portfolio, designed to help restore resources injured by the Deepwater Horizon oil spill. After the spill, federal and state agencies formed the Deepwater Horizon Natural Resource Damage Assessment Trustee Council to assess the impacts and implement actions to restore injured habitats, species, and the services they provide. In 2019, the Open Ocean Trustees selected four MDBC restoration projects, one of which was the CPT project.
Citation: Linde, H. S., Watson, A. M., & Etnoyer, P. J. (2025). Investigating the diet of three mesophotic octocorals using fatty acid biomarkers. Invertebrate Biology, 144(4). https://doi.org/10.71161/ivb.144.4.2025.00030