On an October day in sunny and warm Gainesville, Florida, U.S. Geological Survey (USGS) aquarist Jonathan Quigley walked into a cool, dimly lit lab expecting the day to be like any other. He would come in, care for the corals currently housed in the lab, go home, and repeat the same thing the next day. Instead, he found his fellow USGS scientist, Will Jenkins, excitedly hunched over a dark tank and shining a flashlight onto a small piece of bright orange soft coral. In the spotlight created by the flashlight, tiny eggs, smaller than mustard seeds, emerged from the white tipped coral polyps. Suddenly, Quigley realized this day would not be like any other. 

Quigley and Jenkins work in the USGS Wetland and Aquatic Research Center’s benthic ecology lab which is led by Dr. Amanda Demopoulos. This lab, and several others including federal labs, public aquariums, and academic institutions have been growing and caring for corals that typically live on dimly lit portions of the seafloor in the twilight (mesophotic) zone of the Gulf of Mexico, and beyond. This low light zone of the sea floor is too deep for most divers to reach but despite living at remote depths, these corals are still impacted by human activities like fishing, pollution, and even oil spills.  This became apparent when in 2010 the Deepwater Horizon oil spill impacted over 770 square miles of mesophotic and deep seafloor habitat where many corals that live where the light is low or absent thrive. Since 2021, each of these labs have been growing some of the species of corals most affected by the oil spill to help restore the injured ecosystem. 

After finding the reproducing coral, USGS’s team of aquarists Quigley and Jenkins quickly began communicating with two other labs that were growing the same species of corals to see if they had noticed anything new about the corals in their care. One lab responded with the same findings; their bright orange octocoral species known as Swiftia exserta was spawning as well. Synchronous spawning, where corals release their eggs and sperm into the water at the same time, is not uncommon in shallow-water coral species. Based on cues like exposure to light, water temperature, and even the cycles of the moon, corals will release their sperm and eggs at the same time so they will fertilize in the water, settle, and create new corals.  However, for corals that live at deeper depths, reproduction is rarely witnessed and not as well understood. On that October day, two different labs, across the country, became the first to document spawning Swiftia exserta.

Swiftia exserta and other corals that live at similar or deeper depths are not well studied because they live in such a hard-to-reach place. Studying them up close in aquariums makes it possible for people working to restore them to gain new understanding of their biology that would not be possible otherwise. Monitoring these corals in nature for long periods of time is only possible with occasional visits using very expensive, specialized equipment like remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), and landers. By growing them in aquariums, scientists can follow the progress of the corals on a continuous basis to learn traits like how fast they grow, how and when they reproduce, and what ocean conditions they prefer.

For the corals being cared for in the USGS lab, one of the biggest challenges is keeping them fed. Most shallow-water corals have photosynthetic symbiotic algae called Symbiodiniaceae (commonly known as zooxanthellae) that supply up to 95 percent of their energy needs. As long as the lights above the tanks are sufficient, shallow-water corals in aquarium settings are easily satisfied. However, the corals being cared for in Gainesville live where sunlight is low or even absent, so most lack zooxanthellae and derive all their energy from food they catch with their tentacles, a process called “filter feeding.” These corals can be voracious, which means for the USGS aquarist team there are no days off. Three hundred and sixty-five days a year someone must come into the lab and painstakingly feed each branch of coral.

This small but mighty team works to make sure the corals have enough to eat, including aquarist Leigh-Anne Carlson. When it is feeding time, which happens six times a day, Swiftia exserta polyps will fully extend like hungry, grasping hands. Carlson must then use a small pipette (like a dropper) to hand feed each coral polyp. Once given their meal, which often consists of brine shrimp, fish eggs, or other commercially available coral foods, the coral tentacles will curl inwards and envelop their feast. Their diets are also constantly changing, as the aquarist team tries to meet the coral’s changing needs.

In addition to their meals, corals are picky about their living conditions, but the preferences of these corals are still being discovered by the aquarium teams. Since the 1980s, most of the particulars of keeping corals alive and happy in aquariums have been worked out for shallow-water corals. Extensive online message boards, forums, and libraries of scientific literature exist for keeping shallow-water corals alive. Aquarists know exactly what water chemistry, light levels, and food most shallow-water species of corals need to thrive. There is no such body of knowledge for Swiftia exserta and the other deeper-water corals like it.

Such groundbreaking work can be difficult and at times frustrating, but it is not without its rewards. When Cassidy Hudson, who monitors the water chemistry of the USGS lab, first started her job, one of her responsibilities was to keep the nitrate levels in the water low. In shallow-water tanks, high nitrate levels can encourage algal growth and even lead to coral death. However, as time went on, Hudson and her colleagues discovered that their corals, which live where light levels are low, in their tanks appear to thrive at nitrate levels far outside the range that is typically considered acceptable for most shallow-water corals. Since the Swiftia exserta spawning events, the lab has also coaxed other coral species that live at similar depths to reproduce as well. Thesea nivea, a bright purple soft coral, has started reproducing frequently in the lab. Each month the aquarium team collects hundreds to thousands of eggs. Many of the successfully fertilized eggs have now settled and become new baby corals.

With all the new information the teams are learning from caring for these corals in aquariums, scientists can learn how to better restore and protect corals from current and future threats. Coral habitats at any depth can be injured by human activities like oil spills, temperature increases, fishing, marine debris, and invasive species. The aquarium teams are also testing coral fragmentation techniques to boost asexual reproduction and monitoring different materials for coral settlement to better understand which methods may be most effective for mesophotic and deep-sea coral restoration at a larger scale. These are both methods for shallow-water coral restoration that have been rarely tested for deep-water corals. Hopefully with each new discovery this lab, and the others they are working with, are one step closer to repairing seafloor coral habitats in the Gulf of Mexico.