The Deepwater Horizon leak is linked to changes in gene expression in dolphins

Bottlenose dolphins, which live near the Deepwater Horizon oil spill in the Gulf of Mexico, show striking signs of genetic changes linked to a variety of bodily functions, according to a study published Wednesday.

The discovery shows how scientists are discovering the lingering fallout associated with the unprecedented April 2010 disaster that released an estimated 210 million gallons of crude oil off the Louisiana coast and killed 11 people. It is also estimated that more than 80,000 birds and nearly 26,000 marine mammals were killed.

The study focused on dolphins in the heavily polluted Barataria Bay near New Orleans and used blood tests to compare these dolphins to those living in the less polluted waters of Sarasota Bay, Florida.

The researchers subsequently discovered changes in gene expression in the Barataria Bay dolphin population, including genes implicated in immunity, inflammation, reproductive failure, lung problems and cardiac dysfunction. The results were published in the journal PLoS ONE.

These changes are consistent with previously documented health effects, said co-author Sylvain De Guise, a professor in the Department of Pathobiology at the University of Connecticut. He also co-authored another study that found that the dolphin population in Barataria Bay has declined by 45 percent since the disaster. In a study of dolphins that survived the oil spill, De Guise and his colleagues found that nearly 80 percent still suffer from some form of illness, with lung disease being the most common problem.

Bottlenose Dolphins (National Marine Mammal Foundation)

Bottlenose Dolphins (National Marine Mammal Foundation)

This new study used data collected from dolphin health assessments conducted between 2013 and 2018. The team analyzed blood from 60 dolphins from Barataria Bay and 16 from Sarasota Bay, looking for molecular differences through a process called gene expression profiling. This method is a novel way to understand an organism’s health as it has the potential to detect disease early and is easier to perform than traditional veterinary catch-and-release assessments.

The dual purpose of this study was to test and refine this method while attempting to understand the underlying causes of the health outcomes suffered by Barataria Bay dolphins. The study team hopes this method can help identify which marine mammals are at risk of disease in the future.

“We can say that dolphin populations are having an impact, but we don’t really know what underlies the disease and dysfunction that we’re seeing,” said first author Jeanine Morey, a research biologist who was working with the National Marine Mammal Foundation at the time of the study Studies. “Through this molecular work, we are beginning to understand the root of the problem.”

Different triggers can cause changes in gene expression, she said. Changes in gene expression, in turn, trigger the body’s response. Since factors such as water temperature can also cause a change in gene expression, comparing the Barataria Bay dolphins to the Sarasota Bay dolphins helped the team identify exposure to oil contamination as the key difference between the two groups.

Additionally, previous studies evaluating the health of dolphins in Barataria Bay since the oil spill allowed the team to identify which dolphins in their cohort were exposed to oil and which were born after the event. They found that the significant differences they observed came mostly from the dolphins that survived the disaster.

However, younger dolphins are not necessarily free. Some of the most pronounced differences observed in the Barataria Bay group are related to genes related to the immune system. A previous study found that these dolphins had problems with their immune systems as recently as 2018, and subsequent lab tests on dolphin cells and mice suggested these immune differences could be passed on to future generations. Alterations in the immune system increase the susceptibility to infectious diseases, which can also affect the dolphin’s reproductive success.

“The bottlenose dolphin population in Barataria Bay is not doing very well,” De Guise said. “Once the recovery is underway, it would be at the very beginning and would not be dependent on any additional stressors.”

A standstill of the stressors is unlikely. A study released in August found that traces of the Deepwater Horizon spill are still detectable, and new drilling and flood control plans are expected to result in Barataria Bay dolphin deaths if they proceed as planned. Even smaller man-made problems continue to disrupt the dolphins’ lives.

“During these health surveys, we found dolphins that were entangled in fishing lines and nets,” Morey said. “It’s very hard to see these animals suffer.”

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