Kat Kerlin ECO Magazine How disease, warming waters, and ravenous sea urchins combined to kill the kelp and close the red abalone fishery
First the sea stars wasted to nothing. Then the purple urchins took over, eating and eating until the bull kelp forests were gone. The red abalone starved. Their fishery closed. Red sea urchins starved. Their fishery collapsed. And the ocean kept warming. It sounds like an ecological horror movie, but this scenario actually happened between 2013 and 2017. Its lasting impacts continue to affect northern California’s coast today, with another marine heat wave forecast for this winter.
In a study published this week (21 October) in the journal Scientific Reports, scientists from the University of California, Davis, and the California Department of Fish and Wildlife use two decades of kelp ecosystem monitoring data to chronicle the catastrophic shift in 2014 from a robust bull kelp forest to a barren of purple sea urchins. Similar impacts are being observed in kelp forests from Baja California to Alaska.
Uncharted Territory The study shows how bull kelp deforestation triggered the closure of a $44 million recreational abalone fishery and the collapse of the north coast commercial red sea urchin fishery. More than 90 percent of bull kelp and 96 percent of red abalone were lost along 217 miles of northern California coastline within just a few years. Meanwhile, purple sea urchin populations exploded 60-fold between 2014 and 2015. “We’re in the 20th year of this monitoring program, and we can confidently say, this is uncharted territory that we’re in,” said lead author Laura Rogers-Bennett, an environmental scientist with UC Davis Karen C. Drayer Wildlife Health Center and California Department of Fish and Wildlife operating out of the UC Davis Bodega Marine Laboratory. “We’ve never seen purple sea urchins at these densities before. This paper really shows what it takes in terms of multiple stressors to crash a bull kelp forest.”