FORT BRAGG, U.S. — In 2024, I was scuba diving in Northern California’s Casper Cove where the Watermen’s Alliance, a group of ex-abalone sports divers, has been culling purple urchins since 2020. It had been six years since abalone season shut down, following the region’s kelp forest collapse. About 4 meters (13 feet) down, I spotted a few surviving red abalones, their thick-muscled feet showing from under their single shells as they clung to the bottom of boulders. Purple urchins (Strongylocentrotus purpuratus) clustered near them. I also spotted a single white anemone (Diadumene leucolena) and a spiny, bulbous-eyed Cabezon fish (Scorpaenichthys marmoratus) amid scattered stalks of remnant kelp. A short distance away, it was all bare rock and purple pin-cushion-like urchins. It’s different than watching videos of urchin barrens: Aside from being wet and cold and breathing underwater, I was taken by the scale: it’s so expansive, even with only 2 m (6 ft) of visibility in the murky water. As far as you go along the northern rim of the cove, there are purple urchins, thousands and tens of thousands, where a kelp forest once thrived. I spread my arms to measure what I guesstimated was a square meter and counted some 120 urchins. To bring kelp back, that number would have to drop to 2 per square meter. That’s when kelp spores can take hold again. This requires a lot of urchin-smashing, which these divers were carrying out with rock hammers. To clear one acre (less than half…This article was originally published on Mongabay

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