Peer into the water at the tide pools along the Sonoma Coast, and you’ll see what appears to be an alien invasion of bright purple, spiky balls the size and shape of hacky sacks. Here, sea urchins ...

At first glance, it hardly looks like the beginning of a sea-urchin foraging expedition: a circle of 40 people on the grass pretending to be kelp, feet rooted to the ocean floor, swaying from the ...