Bottlenose dolphins living near the Deepwater Horizon oil spill in the Gulf of Mexico show impressive signs of genetic changes associated with a wide variety of bodily functions, according to a study published Wednesday.
The discovery highlights how scientists are uncovering the lasting consequences linked to the unprecedented April 2010 disaster, which released an estimated 210 million gallons of crude oil off the coast of Louisiana and killed 11 people. It is also estimated to have killed over 80,000 birds and nearly 26,000 marine mammals.
The study focused on dolphins in heavily polluted Barataria Bay, near New Orleans, and used blood tests to compare these dolphins to those living in the less contaminated waters of Florida’s Sarasota Bay.
The researchers later discovered changes in gene expression in the Barataria Bay dolphin population, including genes involved in immunity, inflammation, reproductive failure, lung problems and cardiac dysfunction. The results were published in the journal PLoS ONE.
These changes are in line with previously documented health effects, said co-author Sylvain De Guise, a professor in the department of pathology at the University of Connecticut. He is also a co-author of another study that found that the Barataria Bay dolphin population has declined by 45% since the disaster. In an assessment of dolphins that survived the oil spill, De Guise and his colleagues found that nearly 80% still suffer from some form of illness, with lung disease being the most common problem.
This new study leveraged data collected from dolphin health assessments conducted between 2013 and 2018. The team analyzed blood taken from 60 dolphins from Barataria Bay and 16 from Sarasota Bay and looked for molecular differences through a process called gene expression profiling. . This method is a new way of understanding the health of an organism because it has the potential to allow for early detection of disease 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 by trying to understand the underlying causes of the health consequences suffered by dolphins in Barataria Bay. In the future, the study team hopes that this method can help identify which marine mammals are at risk of disease.
“We can say that dolphin populations are experiencing effects, but we really don’t know what’s behind the disease and dysfunction we’re seeing,” said first author Jeanine Morey, a research biologist who worked with the National Marine Mammal Foundation at the time. of the search. the study. “Through this molecular work, we are beginning to understand the root of the problem.”
Several triggers can cause changes in gene expression, she said. Changes in gene expression, in turn, stimulate the body’s response. Since factors such as water temperature can also cause a change in gene expression, comparing Barataria Bay dolphins to Sarasota Bay dolphins helped the team identify exposure to oil contamination as a defining difference between the two groups.
In addition, because of previous studies that assessed the health of dolphins in Barataria Bay since the spill, the team was able to identify which dolphins in their cohort were exposed to the oil and which were born after the event. They found that the significant differences they observed stemmed primarily from the dolphins that survived the disaster.
However, younger dolphins are not necessarily free. Some of the most pronounced differences seen in the Barataria Bay group are linked 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 and mouse cells suggested that these immune differences could be passed on to future generations. Changes in the immune system increase susceptibility to infectious diseases, which can also affect the dolphin’s reproductive success.
“The Barataria Bay dolphin population is not doing very well,” said De Guise. “If recovery is ongoing, it will be early on and would not be dependent on any additional stressors.”
A standstill from stressors is unlikely. A study released in August found that traces of the Deepwater Horizon spill are still detectable, and new drilling and flood protection plans are expected to result in the death of Barataria Bay dolphins if they go ahead as planned. Even minor man-made problems continue to disrupt dolphin lives.
“When we went out for these health assessments, we found dolphins trapped in fishing lines and nets,” Morey said. “It is very difficult to see these animals suffering.”