Two years ago last week, on April 20, 2010, an explosion on the oil-drilling rig Deepwater Horizon caused the largest marine oil spill in history, gushing nearly 5 million barrels of crude oil over the course of three months.

And, since then, researchers have been hard at work to understand how the oil spill impacted life in the Gulf of Mexico. It’s too soon to say whether the ecosystem is out of the red – it’s only been two years, after all! – but many researchers have been shocked at the ecosystem’s recovery.

“Like everybody else, I had visions of just gobs and gobs of oil smothering thousands of acres of salt marsh,” says James Morris, who studies marshland plants at the University of South Carolina. “But that didn’t really happen.”

As you can see in this slideshow, the marsh grasses are growing back despite being killed off two years ago by the oil. “The plants out there are really tough as nails,” says Morris. “Animals will probably be more susceptible than the plants are, but plants, after all, are the foundation of the ecosystem. If the plants are there, the animals will come back.”


CREDIT: 

Petty Officer 3rd Class Cory J. Mendenhall, U.S. Coast Guard

While the Gulf is not oil-free, far less of the oil stuck around than scientists expected – thanks, in part, to oil-eating microbes. Because there are many natural oil seeps on the Gulf’s seafloor, these microbes already called the Gulf home and were more than happy to feed on the new source of food introduced by the spill. The water in the Gulf is also very warm – especially compared to Alaskan waters, where the last major US oil spill occurred in 1989 – boosting the microbes’ metabolisms and enabling them to gobble up the oil faster.

These are good signs for the ecosystems as a whole, but it doesn’t mean everything is coming up roses. Scientists still have much to learn: how long the oil will stay in the food chain; whether the coral communities will rebound; whether dolphins and other marine mammals will return; whether the fisheries – including the endangered Bluefin tuna -- will recover. And it’s going to take more years of research to tease apart what changes are the results of the spill or dispersant chemicals used to clean up the spill, and which are just normal variations in the ecosystem.

For example, soon after the oil spill, researchers noticed that the number of small fish in the Gulf had decreased pretty dramatically. At first they were worried: had the oil destroyed their nursing grounds? But it’s also possible that the fishing ban, which went into effect soon after the spill, allowed predatory fish to rule the waters – snacking on every small fish in sight. It could be the nursing grounds, the fishing ban, some combination of the two, or other unknown factors.

Only one thing is certain: that scientists need more time to fully understand the impacts of the oil spill. “There’s still a lot we don’t know about how this spill altered the food web of the Gulf of Mexico ecosystem,” says Samantha Joye, who studies marine chemistry and microbes at the University of Georgia. “We’re trying to understand very complicated interactions and feedbacks in a dynamic, constantly-changing system, and it’s going to take time.”

To learn more about the oil spill, flip through this photo essay about what scientists have learned about the ecosystem's communities in the past two years. You should also check out this feature on the Deepwater Horizon oil spill, published two years ago at the time of the spill, and watch these fabulous videos from the Woods Hole Oceanographic Institute about their research in the Gulf and how it's been affected by the spill.