On April 20, 2010, an explosion on the oil-drilling rig Deepwater Horizon caused the largest marine oil spill in US history, gushing nearly 5 million barrels of crude oil over the course of three months. In the two years since, researchers have been hard at work studying the impacts of the spill. See photos and read about some of the things they've learned about the oil spill's impact on pelicans, dolphins, and corals in this slideshow, and read more in this blog post. Even more about the Gulf oil spill can be found in our Gulf oil spill featured story.
slideshow

Oiled Seaweed after the Gulf Oil Spill
Credit: Georgia Department of Natural Resources
Marshes Recover from Oil
Credit: NOAAAfter the oil spill, brown oil flooded marshes in the Mississippi Delta, shown here. But now, to the surprise of many scientists, the salt marshes and plants along the edge of the Gulf of Mexico are relatively free of oil. “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.”

Pelicans Return to Roost
Credit: James Morris, University of South CarolinaTwo years after the Deepwater Horizon oil spill, brown pelicans roost on a mangrove island at the spill's "ground zero," said James Morris of the University of South Carolina. "The impact to this island was great. The recovery is impressive." Read more about ongoing research at the oil spill's two-year anniversary on the blog.

Few Dolphins Have Returned
Credit: NOAAThese striped dolphins dove through oil in the Gulf of Mexico just a few days after the Deepwater Horizon oil spill. Fewer marine mammals have been seen in the area since the spill. "Are they avoiding the water because it doesn't have food supplies anymore? It's hard to say," said Samantha Joye, a marine chemist at the University of Georgia. "But if the upper food web is showing impacts, that means the lower food web has been impacted."

Deep Sea Corals Hit Hard
Credit: Chuck Fisher, Penn State UniversityIn 2010, scientists from NOAA and Woods Hole exploring in the deep regions of the Gulf of Mexico came upon damaged coral reefs covered in a brown substance. And a March 2012 analysis suggests that this brown substance is from the Deepwater Horizon oil spill. "Corals are not fast-growing organisms: it's probably a reasonable assumption that these communities are going to take many, many years to recover," said James Morris of the University of South Carolina.

Oil is Disappearing
Credit: Terese Collins, On Wings Of CareBonny Schumaker, cofounder of the nonprofit On Wings of Care, flies over the Gulf of Mexico oil spill area every few weeks to survey for wildlife—and on April 6, 2012, when this picture was taken, she was pleasantly surprised. "We were pleased to see very few of the surface oil slicks we've seen on every previous flight for the past nearly two years," she wrote on her blog.

Oil Spill Research Continues
Credit: Chris Reddy, Woods Hole Oceanographic InstitutionGulf of Mexico beaches are scattered with these oil-laden "sand patties," as Chris Reddy, who studies oil decomposition at WHOI, calls them. He took this photo on April 19, 2012 as he collected them at Grand Isle, Louisiana to better understand how the oil breaks down—and he plans to continue collecting them for a decade. Read about other ongoing research on the blog.