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Oil spills are bad enough. But toss some sunshine into the mix and it could spell disaster for some marine animals.
Marsh-dwelling sea anemones are a case in point. Cory Berger, an MIT-WHOI Joint Program student who has an affinity for these tiny tentacled creatures (scientifically known as Nematostella vectensis), has been studying their physiological responses to chemical pollution in the Tarrant Lab—oil spills, in particular. And he’s found that phototoxicity—when sunlight makes chemicals more toxic—can occur when the anemones are exposed to both oil and ultraviolet (UV) light in their murky salt marsh homes.
“We think that animals living in shallow coastal waters might be extra vulnerable to oil spills,” says Berger. “This is because sunlight, and especially ultraviolet radiation, interacts with chemicals in the oil and can enhance their toxicity. Because these anemones are a common salt marsh animal that live all over the U.S. East Coast, and are exposed to UV radiation, they were an ideal model organism for this study.”
The fact that these centimeter-sized creatures are translucent was also helpful, as it allowed UV rays to easily penetrate their bodies.
To see if the double whammy of oil and sunlight would be more harmful to the anemones than just oil alone, Berger put live samples into Petri dishes—three to a dish—and exposed the animals to various levels of oil and sunlight over a 24-hour study period.
The oil, which originated from the 2010 Deepwater Horizon spill and had become weathered in the ocean from wave action, evaporation, and sunlight, was dissolved in a diluted seawater so it could be absorbed into the anemone’s permeable bodies. Berger and his colleagues, including WHOI senior scientist Ann Tarrant and WHOI marine chemist Collin Ward, used a solar simulator machine as a light source, which allowed them to control the type and amount of light that the animals were exposed to.
Four groups of anemones were studied: one received both oil and ultraviolet radiation, and another received oil with only non-UV visible light. The other two groups were not exposed to oil: one received UV, and a control group was exposed only to non-UV visible light. This allowed Berger to separate the individual effects of oil and UV and identify effects that were unique to the combined oil and UV treatment.
After each group went through 24 hours of exposure and the data were analyzed, it became clear that the anemones that had been exposed to both oil and UV rays were affected the most.
“We saw a much larger stress response in the animals that were exposed to both,” says Berger. “They activated a bunch of genes involved in stress response, which were probably responding to oxidative stress caused by the combo of oil and ultraviolet radiation.”
Berger leveraged computational techniques to detect these molecular responses and the specific genes within the animals that were triggered. These genes might help to metabolize and detoxify the pollutants, or react to the oxidative stress caused by the interaction with UV.
The findings could have implications for how scientists study the impact of oil spills on marine life in the future. Ward says that most studies investigating how chemicals are toxic to marine life rely on fresh (non-weathered) crude oil, and don’t usually include the added stressor of the sun.
“Scientists haven’t fully considered the interactions between sunlight and oil and how they may harm animals in the ocean,” says Ward. “It’s been an overlooked line item in the toxicity budget and one that needs to be accounted for. With our study, we tried to better represent the modes of toxicity that occur in nature—where these variables actually occur.”
This research is funded by a grant from the Coastal Ocean Institute at the Woods Hole Oceanographic Institution (WHOI), and by WHOI's Investment in Science Fund.