When the Deepwater Horizon drilling rig exploded in April 2010, at least 130 million gallons of oil escaped into the northern Gulf of Mexico over the course of nearly three months. The spill caused immediate environmental damage, coating birds, sea creatures, and coastal marshes alike.
The long-term effects of the catastrophe are still being studied. That the oil is present in the planktonic food web of the Gulf’s waters has already been established. Now, thanks to researchers from Louisiana State University and Austin Peay State University, we know that it has also been incorporated into the tissues of a terrestrial vertebrate — the Seaside Sparrow.
The sparrow is a year-round resident of Louisiana’s salt marshes, and eats a wide variety of aquatic and land-based invertebrate prey. Birds and other animals incorporate isotopes of various elements into their tissues from the food they consume, creating unique molecular “signatures” that scientists can use to understand dietary origins and food chains, among other things.
Two carbon isotopes are absent or reduced in fossil carbon (such as oil) but are abundant in organic matter such as live insect prey. Knowing this, the researchers looked at the relative levels of carbon isotopes in sparrows from both contaminated and oil-free sites.
The results indicated that sparrows from contaminated sites had incorporated carbon from oil into their tissues, providing the first evidence that Deepwater Horizon oil had entered the land-based food web.
An earlier study had found that the same sparrow population had experienced reduced reproductive success for at least two years following the spill. It was once thought the falloff may have been due to a reduction in prey or vegetation cover, but the current research suggests direct toxicological effects may have been a contributing factor.
The research appeared in Environmental Research Letters. — Julie Craves
Read the paper
A. Bonisoli-Alquati, P.C. Stouffer, R.E. Turner, S. Woltmann, and S.S. Taylor (2016) Incorporation of Deepwater Horizon Oil in a Terrestrial Bird. Environmental Research Letters, Vol. 11: 114023.
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