There’s something fishy going on New York City’s East River, and researchers have used DNA collected from the water to work out what it is. A study in PLOS One shows how the technique can be used to monitor not just fish populations, but also land-based wildlife and the diets of New Yorkers.
DNA is the genetic material found inside the cells of living things. Each species has its own unique DNA sequence, which can be used to identify it. As they move around, species shed DNA into the environment from their hair, skin, scales, faeces and other bodily bits. This environmental DNA or ‘eDNA’ can be collected from water, soil and air samples, and used as a non-invasive way of studying the organisms that are out there.
Researchers wanted to find out what lives in the East River, a rocky, estuarine channel sandwiched between Manhattan and the Bronx, and Queens and Brooklyn. So, they took water samples every week for a year and analysed its eDNA.
"We were most surprised about how many fish species migrate in and out of the harbour,” says Mark Stoeckle from The Rockefeller University. This was reflected in seasonal patterns of eDNA. There was 10 times more eDNA in the summer than in the winter, when some species head off to warmer waters.
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eDNA methods are particularly good at detecting species that exist in low numbers. In this case, the researchers were able to detect that two species that were uncommon 10 years ago – skilletfish and feather blenny – had increased in abundance.
There was eDNA from non-fish species too. Researchers were able to identify the presence of wildlife species that live in and around the river, such as rats, beavers and raccoons.
The team also found eDNA from humans and animals that humans eat, including chickens, turkeys, cows and non-local fish. Levels of eDNA from these animals correlated with those of human eDNA, suggesting they could be traced back to wastewater that had contaminated the river. In other words, New Yorkers ate certain animals. Traces of the animals’ DNA survived in the humans’ faeces, which then ended up in the river.
"We think that urban estuary DNA can give a pretty good idea of what local city dwellers eat,” says Stoeckle. “We found that the amount of food animal DNA in the East River fits closely with national sales data. Chicken was number one, then beef, then pork, then turkey.”
Top image: East River, New York City. Credit: Aldo R. Altamirano/Getty Images
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