Kelp forests off the coast of California have declined dramatically since 2014, with large areas being replaced by a carpet of sea urchins. However, there are often healthy patches of forest next door – and a study from the University of California, Santa Cruz has shown that it’s sea otters’ green paws that help them thrive. Sea otters are a ‘keystone species’: they play a disproportionately important role in their ecosystem, influencing the populations of the plants and animals that live there. In particular, they protect kelp forests by preying on sea urchins. Two separate environmental factors have been taking a harsh toll on California’s kelp forests. An unprecedented marine heatwave known as ‘the Blob’ hit the Northeast Pacific in 2014, at the same time as the unusually warm ocean conditions known as El Niño came up from the south. Kelp grow best in cold, nutrient-rich water. Giant kelp is one of the world’s fastest-growing organisms, and in ideal conditions can grow up to around 60 cm in a single day. But with the heat from the Blob and El Niño, the kelp’s growth rate dropped dramatically. A further threat to the kelp began a year earlier. In 2013, […]

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