In spring 2011 stillborn and newborn bottlenose dolphins washed up dead on Gulf coast beaches from Louisiana to Alabama in unusually high numbers. These tiny dolphins, less than 115 centimeters long, died either before birth or soon after, perhaps from their mother's exposure to cold temperatures or to the oil released from the Macondo well for 87 days in the spring of 2010 when these babies were conceived. Yet there was no uptick in baby bottlenose dolphin deaths in Florida or Texas, areas that saw relatively little oil from BP's spill. In fact, living bottlenose dolphins from those areas got a relatively clean bill of health when examined by researchers a year after the spill whereas dolphins from Barataria Bay in Louisiana—the oiliest place in the wake of the Gulf oil spill—had a series of health issues, and one pregnant female was carrying a dead fetus.



From June 2010 through June 2013 there were four mass strandings of dead dolphins on Gulf coast beaches stretching from the Texas–Louisiana border into Florida—three after the beginning of the disaster on the Deepwater Horizon drilling platform that saw BP's Macondo well blow out. After ruling out previous causes of such mass deaths—cold weather, disease like morbillivirus and even poisoning by algal bloom—fisheries scientists are left with only one conclusion: "Put all that evidence together and it supports the hypothesis that the oil spill contributed to the increase in deaths," says veterinarian Stephanie Venn-Watson of the National Marine Mammal Foundation in San Diego.



Bottlenose dolphins examined in the Gulf of Mexico in the wake of the disaster showed signs of adrenal and lung disease consistent with exposure to petroleum. Plus, a record of mass strandings from 1990 to 2009 showed the unusual nature of these more than 1,000 dead dolphins in just three years. The year 2011 stood out in that 32 specific families of bottlenose dolphins were hardest hit in Alabama, Louisiana and Mississippi, with more deaths recorded than in previous years; Louisiana had the highest number of dead dolphins ever recorded in that state in 2010 and 2011. These "unusual mortality events" continued through at least summer 2014. "There are some pretty demonstrable effects in terms of things like dolphin exposure," says biologist Christopher D'Elia of Louisiana State University and dean of the School of the Coast and Environment. Scientists have "found indicators of stressors in dolphins that they attributed to oil effects."



It's not just dolphins. Shrimp, oysters and other sea life have suffered from the oil and dispersants. "Zooplankton in September 2010 that are supposed to be pink—they were black," says biogeochemist Samantha Joye of the University of Georgia, noting that oil clung to the outside of everything from cellular life on up. "Some oil was moving up the food web." In addition, the deep-cleaning operations on beaches that followed the spill carted away crabs and other hidden shore life along with tar mats. Marshes that harbored oil had a different set of insects than less affected swamps, and in some the oil killed off plant life, allowing Gulf waters to wash away more land. "The edge of the marsh has been knocked back farther and more land has been lost," D'Elia says. The stress of the oil spill—as well as the air pollution—has not been good for people either.



The sea life around the wellhead itself has recovered to some extent. Where nothing lived in 2010 there are now at least a few fish, crabs, amphipods, shrimp, mounds that reflect burrowing organisms and even vampire squid. "It's impossible to say if it's back to normal because we don't know what normal was," Joye notes. "It's a lot better than it was in 2010."



But, like the missing oil, the effects of the blowout on deep-sea life—whether sperm whales or sea cucumbers—may be hard to find given the mysteries surrounding the lives of these animals. "Bottlenose dolphins are coastal—if they die, they're more likely to end up on the beach," Venn-Watson notes. "They're serving as a sentinel of potential impact of oil on sea life." Ongoing surveys as part of the Natural Resource Damage Assessment suggest that life for the 32 bottlenose dolphin families that live in the Gulf is getting better, although chronic lung disease persists in the worst hit communities.



But it remains hard to tell what's going on with the dolphins because so much is unknown about what their life was like before the spill. "What is the baseline population of tuna? What is the baseline health of all these species?" asks marine chemist Chris Reddy of Woods Hole Oceanographic Institution. "Do we know five years later who is in good health and who we should be worried about?"



Full autopsies of the dead dolphins will deliver more answers, results that are forthcoming. "I want to look at the tissues. What do they look like? What are they telling us happened to them?" asks Venn-Watson, who is also studying how life in the Gulf is still changing today. "We need to be able to look at those tissues to get closer to the truth."