Sea otters save marshes
Anew study shows that sea are having a positive impact on salt marshes (wetlands located near the sea) in California, US. This is because the otters eat shore crabs, stopping them from damaging the habitat.
The study was published in January and is based on decades worth of data collected around Elkhorn Slough, a salt marsh in California that is home to the state’s largest sea otter population.
Salt marshes are very important. They support a lot of wildlife; they soak up carbon dioxide (a gas that causes climate change); and they stop pollution washing out to sea. Salt marshes are a very threatened habitat, partly because of rising sea levels causing erosion (wearing away). However, erosion at Elkhorn Slough had begun to slow and the scientists suspected this was because of the sea otters.
During the 18th and 19th century, sea otters were hunted for their pelts (fur coats) and almost went extinct. Since laws were created to protect them, their numbers have steadily grown and they returned to Elkhorn Slough in the 1980s. To measure their effect, the researchers collected observations on the ground and used aerial photography dating back to the 1930s to see how the salt marsh had eroded over time. They also carried out experiments, allowing otters to settle in some places but blocking them from others. The results showed that in areas where there were lots of sea otters, erosion slowed by an average of 69%.
Co-author of the study, Brent Hughes, said that otters slow erosion by eating shore crabs. These crabs dig down and eat the roots of the plants that hold the salt marsh together. If left to themselves, the shore crabs would fill the marsh with holes, like “Swiss cheese”, said Hughes, allowing it to wash away. Luckily, sea otters eat more than 25% of their body weight daily – and they love the taste of shore crab.