Collapse of kelp forest imperils North Coast ocean ecosystem
Large tracts of kelp forest that once blanketed the sea off the North Coast have vanished over the past two years, a startling transformation that scientists say stems from rapid ecological change and has potentially far-reaching impacts, including on several valuable fisheries.
The unprecedented collapse has been observed along hundreds of miles of coastline from San Francisco to Oregon. The region's once-lush stands of bull kelp, a large brown alga that provides food and habitat for a host of wildlife species, have been devoured by small, voracious purple urchins. In the most-affected areas, denuded kelp stalks are almost all that remains of plant life.
Scientists have described the landscape left behind as an “urchin barren.” Other factors, including warmer water, also are to blame, they say.
“It's no longer a kelp forest,” said Cynthia Catton, an environmental scientist with the California Department of Fish and Wildlife, stationed in Bodega Bay.
Laura Rogers-Bennett, another Bodega Bay scientist, said it is as if whole terrestrial forests were disappearing, only in this case they are underwater and out of sight.
“A lot fewer people swim through the kelp forest,” she said. “But if they do right now, they‘re going to really see that there are huge changes that have taken place in the last year and a half or so.”
The discovery has taken shape as California scientists and policy makers are raising a broader alarm over the ebbing health of ocean waters, pointing to their increasing warmth, acidity and other conditions that have affected wildlife and the fishing industry.
The state's commercial Dungeness crab fleet has endured a disastrous year, with fishermen forced to sit out the most lucrative months of their season over health concerns presented by a naturally occurring neurotoxin. Its prolonged presence in the sought-after crustaceans, which account for California's single- most valuable ocean fishery, at more than $60 million, was tied to the same warm-water conditions impacting kelp beds.
The extended drought, meanwhile, has contributed to a grim forecast for the upcoming commercial salmon catch - the second-most valuable fishery, worth more than $12 million two years ago. The projection has salmon fishermen from Eureka to Morro Bay bracing for their second consecutive meager year.
The kelp collapse may only add to the woes for some.
Purple urchins are a silver- dollar-sized species rarely caught for commercial harvest in California. They normally co-exist in kelp forests alongside other marine life, including red urchins - which support a fishery worth $3.1 million on the Mendocino and Sonoma coasts and $9.1 million statewide - and red abalone, which draw legions of sport divers to the region each year from April to November.
But those two species also feed on kelp and both are showing signs of starvation, Catton said.
Rockfish, another key fishery that includes dozens of species sought by commercial and sport anglers, also likely will take a hit from the kelp die-off, said Mark Carr, a professor of ecology and evolutionary biology at UC Santa Cruz. The young of several near-shore species take shelter in the kelp during their first months of life.
In Sonoma and Mendocino counties, commercial landings of rockfish totaled nearly $500,000 in 2014, according to the latest state records. Statewide, the fishery brought in $2.7 million.
“There's almost no rockfish species that is not of economic importance,” said Milton Love, a rockfish expert and associate research biologist at UC Santa Barbara's Marine Science Institute.
The young of many rockfish species also are a major food source for seabirds, salmon and some pinnipeds, like sea lions. A major collapse of those populations could snap the food chain.
“It's very concerning,” Catton said. “There's a lot of uncertainty moving forward.”
‘A perfect storm'
Scientists blame the current situation on what some have called “a perfect storm” of large-scale environmental impacts dating back to 2011, when a harmful algal bloom off the Sonoma Coast released toxins that killed large numbers of red abalone and took a toll on other invertebrates.
In 2013, an eruption of sea star wasting disease along the West Coast eliminated vast quantities of starfish, affecting about 20 species to varying degrees, including at least two with pivotal roles in the food web.
Starfish are the primary predators of purple urchins, particularly in areas like Northern California, where sea otters - another significant urchin eater - have not rebounded as they have begun to do elsewhere on the coast.
Without such predators to keep them in check, the density of purple urchins on the North Coast reportedly now is more than 60 times that observed in the past, Catton said.