National Fisherman: Pacific urchins: California divers fight the purps; 1.2 million ground up for compost
Purple urchins continue to plague divers seeking out red urchins throughout California. Blamed on the warm-water Blob, El-Niño and other environmental factors, large beds of giant and bull kelp disappeared, which not only provided food for the red urchins, but contributed to plump egg skeins headed for markets.
The absence of the kelp led to the decimation of the sea star, a key predator that keeps populations of purple urchins in check. With the lack of predators and their hardy scavenging characteristics, purple urchins can thrive on a nearly naked seafloor and get by on a fraction of the nutrients required by red urchins and other critters.