Leiopathes, also known as black corals, are some of the oldest organisms in the sea. Peter Etnoyer, Author provided
Corals are fascinating animals. Just like there would be no forests without trees, there would be no coral reefs without corals. Even in the dark, cold waters of the deep sea, corals thrive and a myriad of other organisms live in, on and around their branches. No matter where they are found, corals grow slowly and some species get very, very old.
The Redwood of the deep ocean is the black coral, Leiopathes glabberima (pictured above). Some colonies have been found to be over 4,000 years old. Yet, these deep-water corals are increasingly exposed to human activity associated with mining for oil and minerals. The five-year anniversary of the Deepwater Horizon oil spill, the largest spill in history, is a stark reminder of that.
In the aftermath of the oil spill, I was among the army of scientists who conducted experiments and surveys to document the impact of the spill and monitored the Gulf for signs of recovery (see in BioScience). However, I began my research career studying how tropical, shallow water corals react to a warming ocean. Field work consisted of scuba diving in breathtakingly beautiful coral forests.
The contrast to the deep Gulf of Mexico couldn't be starker and this contrast was partly what fascinated me about the deep sea. How do corals thrive in the dark and cold?
The oil spill gave my research a new direction. I shifted my focus to study how corals respond to chemical stressors such as oil and the dispersant Corexit, which was used to turn the oil into smaller droplets in the aftermath of the spill.
Working with my colleague Erik Cordes at Temple University and our students, we found that in laboratory experiments corals were more sensitive to dispersant and dispersed oil than oil alone. These findings were just published in a special issue of Deep Sea Research II.
We sampled corals from the vicinity of the oil spill site in the Gulf of Mexico with a remotely operated vehicle and exposed them to a range of concentrations of crude oil from the spill site. We also exposed them to the dispersant Corexit 9600 used during the oil spill clean-up and mixtures of oil and dispersant.
Villages at sea: an oil platform in Gulf of Mexico. Sean Gardner/Reuters
At the tested concentrations, the corals showed a range of stress responses such as sloughing tissue and excess mucus and increased mortality in response to dispersant and dispersed oil compared to oil alone. Even before the corals showed any outward signs of stress we could detect that they were shutting down their regular cellular machinery and instead they were expressing a few genes characteristic of stress.
These experimental findings from the laboratory are in line with what has been found for shallow water corals and with data that shows coral mortality at sites directly impacted by the oil spill.
This calls into question whether the application of dispersant as a clean-up procedure after oil spills is warranted.
On the other hand, responders face difficult decisions in the aftermath of a spill and the dispersant does keep the oil off the beaches and may help seabirds and other animals. Clearly, prevention of spills is the best cure.
What surprised me when I first started sailing on research vessels in the Gulf of Mexico is the sheer number of oil platforms out there. At night, standing on deck to enjoy a starry night, one often is surrounded by these large platforms that appear like floating, lit-up cities against the black sky and water.
In looking out at the wells at night, I asked: which one is going to be the next Deep Water Horizon?