Marine life is still struggling after the Deepwater Horizon oil spill

It wasn’t just the coastline and the ocean surface that was drenched in oil after the Deepwater Horizon spill in 2010. Life in the deep sea took a hit, too, and many species in the region are still drastically reduced in number.

“The health of our overall oceans also requires a healthy deep sea, as the deep oceans serve vital roles in carbon cycling, marine food webs, and overall ocean function,” says Craig McClain at the Louisiana Universities Marine Consortium. He and his colleagues used remotely operated underwater vehicles to survey the Gulf of Mexico around the site of the disaster. They did the survey in June 2017 and compared their findings with surveys done in the two months directly after the oil spill.

While the number of animals increased in that time, the diversity was lower. McClain says he and his team noticed an absence of sea cucumbers, fly-trap anemones, Venus flower basket sponges, and giant isopods – crustaceans that look like large woodlice.

There has also been a change in which animals inhabit the area. The communities seen in 2010 and 2017 were less than 20 per cent similar in composition.

Surprisingly, they found an abundance of arthropods, including the red shrimp Nematocarcinus, a white caridean Glyphocrangon shrimp, and the Atlantic deep sea red crab. McClain says they may be attracted to the site because the hydrocarbons that break down in the wake of an oil spill can mimic the chemicals in sex hormones that they use to find mates.

“This seems to be common in some other oil spills. A historic oil spill in Buzzards Bay in New England attracted the American lobster in droves,” he says. “We believe the hydrocarbons are serving as an attractant and creating a La Brea Tar Pit scenario, where healthy individuals are attracted but are trapped, and may eventually die, at the site.”

They may die there because the chemical signals may also deter other animals they prey on from entering the area.

The sampling McClain and his team did were at deeper sites than the Deepwater Horizon well, but he says that at these depths in the Gulf of Mexico, we wouldn’t expect to see much difference in diversity. “We are confident that the differences of the Deepwater Horizon site specifically reflect environmental damage related to the oil spill,” he says.