https://www.theguardian.com/environment/2020/aug/14/natures-furry-engineers-sea-otters-in-california-estuaries-surprise-scientists-aoe
The Guardian said: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.
“This is the highest nutrient concentration that I had ever seen on the planet,” says Hughes, a biologist at Sonoma State University. “Any model would suggest there should be no seagrass there and yet it was expanding.”
Hughes set out to solve the mystery. He examined every possible factor, including water quality, temperature and changes in seagrass coverage over time, going back 50 years. He was not making any progress until he was approached by a boat captain named Yohn Gideon who had been running wildlife tours in the slough since 1995. Over the years, the captain had handed clickers to his passengers, asking them to count the sea otters they saw.
Hughes overlaid the captain’s sea otter counts with historical seagrass coverage data and realised the two graphs were almost perfectly in sync. When sea otter numbers went up, seagrass went up, too. “You don’t see that very often in ecology. That was a eureka moment,” he says.
...
When the otters first moved into the slough in the 1980s, they put their big appetites to work eating crabs. With fewer crabs to prey on them, the California sea hares – a sea slug – grew larger and became more abundant. The slugs fed on the algae growing on the seagrass, leaving the leaves healthy and clean.
Hughes had discovered a trophic cascade that had made the seagrass beds the healthiest of any estuary he had seen on the west coast. Since the otters arrived in the slough, the seagrass has recovered and increased by more than 600% in the past three decades.
...
Last edited: