The Anemone in the Coal Mine
The starlet sea anemone shows just how extensive the effects of common pollutants can be.
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It’s no secret that the common pollutants nitrate (from fertilizer) and phthalates (from plastic) can harm a variety of organisms, including people. When someone ingests nitrate, for example, it can be converted by the body into nitrite, which interferes with the blood’s ability to transport oxygen. In infants, this can lead to a condition known as blue baby syndrome. Phthalates, meanwhile, are potentially linked to kidney, liver, and reproductive problems in humans. These pollutants can also be devastating for aquatic animals.
A new study led by biologist Karen Echeverri at the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, demonstrates just how extensive the damage from nitrate and phthalate exposure can be. In laboratory tests, Echeverri and her colleagues showed these pollutants can affect everything from an animal’s overall body development to the makeup of its microbiome. Perhaps most strikingly, their study showed that all of these consequences can afflict one organism: the starlet sea anemone.
Native to salt marshes on North America’s Atlantic coast, starlet sea anemones aren’t much bigger than a grain of rice. They look like “a tube with a bunch of spaghetti at the top,” according to Sylvia Klein, one of the study’s authors.
At MBL, Klein tended to plates full of anemone embryos that had been exposed to potassium nitrate and dioctyl phthalate at levels comparable to those present in nearby salt marshes. Klein also raised a cohort in clean salt water as a control group.
Within weeks, Klein began noticing differences. Juvenile anemones’ bodies are transparent, and they eat orange brine shrimp. “You can actually see whether they’re eating or not,” says Klein. But the anemones living in polluted water weren’t eating. They were smaller, too. These observations motivated the researchers to further examine the anemones’ development, says Klein, who is now a graduate student at the University of Minnesota.
The team’s investigations revealed a range of other effects. Pollutant-exposed anemones, the researchers found, have fewer tentacles with which to catch food. They suffered other more subtle changes, too.
Though starlet sea anemones are normally able to regrow severed body parts like their tentacles and pharynx, which they use to eat, those exposed to pollutants were less capable of regeneration. And when the researchers applied a fluorescent stain to the stinging cells on the anemones’ tentacles, they found that polluted anemones had fewer stingers.
Emil Ruff, another researcher at MBL, analyzed the microbial communities living in and on the anemones. These, too, were altered. Ruff found that in the microbiomes of the anemones living in nitrate-laden water there were more bacteria that appeared able to metabolize nitrate. He says it’s possible that these nitrate metabolizers may actually be helping the anemones by processing some of the nitrate that’s harming them. “We don’t know,” he says.
It will take further investigation to explain precisely how all of these changes occur. For now, the research shows the importance of protecting water from pollutants, especially in starlet sea anemones’ native salt marshes.
Preventing nitrate and phthalate pollution is also important for people. After all, says Carys Mitchelmore, an aquatic toxicologist at the University of Maryland who was not involved in the research, the majority of people on Earth—more than half—live near the coast. People living in these areas contribute to pollution, but they’re also affected by it, along with all the other organisms in the ecosystem.
“It’s like a reality check,” says Echeverri, “because you realize that, Oh my goodness, every time we go swimming, we’re drinking this water, too. And all the other animals—microscopic animals that live in the ocean—and plants, they’re all being affected by these pollutants.”
But we don’t tend to think about them, Echeverri adds, “because we can’t see them by eye.”