There were a lot of disruptions at one time that led to this collapse, and the system now persists in this altered state," said first author Meredith McPherson, a graduate student in ocean science at UC Santa Cruz. "It's a naturally dynamic system that has been really resilient to extreme events in the past, but the die-off of sunflower stars caused the resilience of the ecosystem to plummet. As a result, the kelp forests were not able to withstand the effects of the marine heatwave and El Niño event combined with an insurgence of sea urchins."