Furry engineers: sea otters in California's estuaries surprise scientists

It is not just at sea that North America's smallest marine mammals with a huge appetite are benefitting the ecosystem

• Photographs by Isabelle Groc

When Brent Hughes started studying the seagrass beds of Elkhorn Slough, an estuary in Monterey Bay on California's central coast, he was surprised by what he found. In this highly polluted estuary, excessive nutrients from agricultural runoff spur the growth of algae on seagrass leaves, which kills the plants. Yet in 2010, Hughes noticed that the seagrass beds were thriving. It did not make sense.