‘Cockroaches of the ocean’ are eating away California’s underwater forests

The purple urchin is mowing down kelp forests that are crucial as a critical habitat and a source of food for a wide range of species Early on a grey summer Saturday, an unusual assemblage — commercial fishermen, recreational boaters, neoprene-clad divers — gathered for a mission at Albion Cove, a three-hour drive north of San Francisco. “Our target today is the purple urchin,” said Josh Russo, a recreational fishing advocate who organised the event. “The evil purple urchin.” Five years ago, assigning wickedness to the purple urchin, a shellfish the size of a plum with quarter-inch spikes, would have been absurd. That was before the urchins mowed down Northern California’s kelp forests. The underwater forests — huge, sprawling tangles of brown seaweed — are in many ways just as important to the oceans as trees are to the land. Like trees, they absorb carbon emissions and they provide critical habitat and food for a wide range of species. But when climate change helped trigger a 60-fold explosion of purple urchins off Northern California’s coast, the urchins went on a feeding frenzy and the kelp was devoured. Warming ocean “It would be like one of those beautiful deciduous forests turned into a desert,” said Gretchen Hoffman, a professor of marine ecology at the University of California, Santa Barbara. “But in the matter of five years.” The dangers extend far beyond this inlet: Kelp forests exist along the cooler coastlines of every continent but Antarctica. And they are under threat both from rising ocean temperatures and from what those warmer waters bring. Already, Maine’s forests of sugar kelp, a source of the sweetener mannitol, have experienced temperature-linked declines. And in Tasmania, kelp forests have succumbed to a purple urchin outbreak. Here in Albion, they are trying to avoid a similar fate. The divers went to work, scraping purple urchins off the bottom of the cove, hoping it would allow the kelp, which has declined 93 percent in Northern California, to grow back. Cynthia Catton, an environmental scientist with the California Department of Fish and Wildlife, and a small team of interns sat on a boat counting the urchins that divers hauled to the surface, to get a sense of how they were faring. The story of the kelp’s disappearance is the story of an interwoven food system breaking down, and in the process threatening people’s livelihoods. Some of the first people to sound the alarm about the purple urchins, Catton said, were commercial red urchin harvesters. One of them is Gary Trumper, who has harvested red urchins for more than 30 years. Red urchins, larger than purple urchins, are commercially viable because people eat them — or more specifically, their gonads. The delicacy is better known to sushi aficionados as uni. But the increasing purple urchin population outcompeted the red urchins for the available kelp. Without kelp, the red urchins starved. That cut the value of Northern California’s commercial red urchin fishery from $3.6 million in 2013 to less than $600,000 in 2016. Many harvesters have moved on. “It’s probably 10 or 15 guys left doing it in the harbour,” Mr. Trumper said. The trouble began with the starfish. Sunflower starfish, whose appendages can span more than 3 feet, normally eat purple urchins, helping to limit their numbers.

Source : https://www.thehindu.com/todays-paper/tp-life/cockroaches-of-the-ocean-are-eating-away-californias-underwater-forests/article25292145.ece

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