The coastal waters of northern California were once home to undulating forests of bull kelp, a type of seaweed that offers shelter to a host of sea creatures. But a series of adverse ecological events have jolted the region’s marine ecosystem out of whack. Populations of purple sea urchins, a voracious, kelp-eating species, have exploded. And now, according to a new study in Scientific Reports, more than 90 percent of bull kelp canopy along 217 miles of California’s coast is gone.