Diversity along an urbanization gradient

Despite decades of work in environmental science and ecology, estimating human influences on ecosystems remains challenging. This is partly due to complex chains of causation among ecosystem elements, exacerbated by the difficulty of collecting biological data at sufficient spatial, temporal, and taxonomic scales. 

University of Washington and Northwest Fisheries Science Center research has applied eDNA technology to broadly measure the effects of human activity on the environment. In a new paper just published in PeerJ, researchers describe how they used DNA in the waters of Puget Sound, Washington state, to characterize the amount of animal life along highly urbanized shorelines, such as Piper's Creek in Seattle, and in more remote areas with fewer humans, like Vashon Island. This is believed to be the first study that uses genetic markers to understand the impact urbanization has on the environment, specifically, whether animal diversity flourishes or suffers.

The study detected more than 1,600 unique genetic signatures - many representing different species - across Puget Sound, including porpoises, salmon, starfish, barnacles, eagles, and even humans. The colleagues also found that urban Puget Sound shorelines support a denser array of animals than in remote areas. In particular, clams and other mud-dwellers congregate more densely along urban beaches which the researchers consider a surprising find:

Clams and other things that live in mud seem to like living near cities, which is really interesting. It suggests that maybe humans are subsidizing mudflats, or it may just as well be the converse - maybe humans tend to live in really protected areas that are the same environment clams happen to like.

While urban beaches in Puget Sound had more abundant fauna, these areas were also more homogenous in the kinds of species that lived there, the researchers found, suggesting a trade-off between different kinds of diversity between more- and less-urban areas.

We can go out, take a sample of water, and the DNA from thousands of species appears. This way, we don't have to decide if we are going to count snails or orcas when we look at environmental impacts. Instead, we can just look at what's there.