Gulf's dolphins pay heavy price for Deepwater oil spill

A new study of dolphins living close to the site of North America's worst ever oil spill – the BP Deepwater Horizon catastrophe two years ago – has established serious health problems afflicting the marine mammals.

The report, commissioned by the National Oceanic and Atmospheric Administration [NOAA], found that many of the 32 dolphins studied were underweight, anaemic and suffering from lung and liver disease, while nearly half had low levels of a hormone that helps the mammals deal with stress as well as regulating their metabolism and immune systems.

More than 200m gallons of crude oil flowed from the well after a series of explosions on 20 April 2010, which killed 11 workers. The spill contaminated the Gulf of Mexico and its coastline in what President Barack Obama called America's worst environmental disaster.

The research follows the publication of several scientific studies into insect populations on the nearby Gulf coastline and into the health of deepwater coral populations, which all suggest that the environmental impact of the five-month long spill may have been far worse than previously appreciated.

Another study confirmed that zooplankton – the microscopic organisms at the bottom of the ocean food chain – had also been contaminated with oil. Indeed, photographs issued last month of wetland coastal areas show continued contamination, with some areas still devoid of vegetation.

The study of the dolphins in Barataria Bay, off the coast of Louisiana, followed two years in which the number of dead dolphins found stranded on the coast close to the spill had dramatically increased. Although all but one of the 32 dolphins were still alive when the study ended, lead researcher Lori Schwacke said survival prospects for many were grim, adding that the hormone deficiency – while not definitively linked to the oil spill – was "consistent with oil exposure to other mammals".

Schwacke told a Colorado based-publication last week: "This was truly an unprecedented event – there was little existing data that would indicate what effects might be seen specifically in dolphins – or other cetaceans – exposed to oil for a prolonged period of time."

The NOAA study has been reported at the same time as two other studies suggesting that the long-term environmental effects of the Deepwater Horizon spill may have been far more profound than previously thought.

A study of deep ocean corals seven miles from the spill source jointly funded by the NOAA and BP has found dead and dying corals coated "in brown gunk". Deepwater corals are not usually affected in oil spills, but the depth and temperatures involved in the spill appear to have been responsible for creating plumes of oil particles deep under the ocean surface, which are blamed for the unprecedented damage.

Charles Fisher, one of the scientists who jointly described the impact as unprecedented, said he believed the colony had been contaminated by a plume from the ruptured well which would have affected other organisms. "The corals are long-living and don't move. That is why we were able to identify the damage but you would have expected it to have had an impact on other larger animals that were exposed to it."

Chemical analysis of oil found on the dying coral showed that it came from the Deepwater Horizon spill.

The latest surveys of the damage to the marine environment come amid continued legal wrangling between the US and BP over the bill for the clean-up. BP said the US government was withholding evidence that would show the oil spill from the well in the Gulf of Mexico was smaller than claimed. Last week BP, which has set aside $37bn (£23bn) to pay for costs associated with the disaster, went to court in Louisiana to demand access to thousands of documents that it says the Obama administration is suppressing.

The US government is still pursuing a case against BP despite a deal the company reached at the beginning of March with the largest group of private claimants. That $7.8bn deal, however, does not address "significant damages" to the environment after the spill for which BP has not admitted liability. And it has not only been the immediate marine environment that has been affected. A study of insect populations in the coastal marshes affected by the catastrophe has also identified significant impact.

Linda Hooper-Bui of Louisiana State University found that some kinds of insect and spider were far less numerous than before. "Every single time we go out there, the Pollyanna part of me thinks, 'Now we're going to measure recovery'," she said. "Then I get out there and say: 'Whaaat?'"

She had expected that one group of arthropods might be hit hard while others recovered, but her work, still incomplete, shows a large downturn among many kinds. "We never thought it would be this big, this widespread," she said.

For its part BP has claimed in a recent statement that it has worked hard to fulfil its responsibility to clean up after the spill. "From the beginning, BP stepped up to meet our obligations to the communities in the Gulf Coast region, and we've worked hard to deliver on that commitment for nearly two years," BP chief executive Bob Dudley declared recently.