To address the drastic decline in bull kelp along the Northern California coast, the Greater Farallones Association released a recovery plan last month to inform future management decisions. Purple urchins play an important role in the plan: the species, booming since the die-off of sea stars on the Pacific coast, have decimated kelp forests.
The recovery plan culminates a two-year effort from 25 stakeholders, including fishermen, tribespeople and scientists. Prepared for the Greater Farallones National Marine Sanctuary and the state Department of Fish and Wildlife, it identifies ways to address the loss of bull kelp, which provides essential food and habitat for thousands of marine species.
According to Fish and Wildlife, bull kelp forests off the coast of Sonoma and Mendocino Counties declined 93 percent since 2014 due to a “perfect storm of ecological impacts,” including increased ocean temperatures, algal blooms and soaring populations of kelp predators such as the purple urchins. Though the report focuses on the waters off the shores of the two counties where the problem is the most dire, Marin’s kelp forests have also suffered—as have those across the state.
The report outlines possible sites for restoration, guidelines for future monitoring and research, and community engagement. “Our purpose was to encourage restoration but also to be resilient and forward thinking, innovative. The disappearance of our once-vibrant bull kelp forest is where we are,” said Francesca Koe, a free diver who sits on the advisory council for the Greater Farallones sanctuary and co-chaired the working group that produced the report. “For instance, we recommend finding a beneficial use for the purple urchin: maybe we would find out the feasibility of actually fattening up the urchin and opening up a fishery. Right now, they are just overgrazed skeletons.”
The population explosion of purple urchins, which consume bull kelp, followed the mysterious loss of one of their primary predators: sea stars. Since 2013, sea stars along the Pacific coast have been taken by a disease known as sea star wasting syndrome. Some research suggests that the wasting disease—which has affected keystone species like sunflower stars and rainbow stars most severely, though many other star species are now declining in equally rapid numbers—is the result of a virus, though others suggest environmental factors like warmer waters.
The same disease caused star die-offs in the 1970s, ‘80s, and ‘90s, but not to such a degree; some species have more or less disappeared in California. In their absence, purple urchins have been free to decimate kelp forests.
Other factors have contributed to the kelp decline, too, including warmer ocean temperatures. Around the same time that the starfish began dying, a mass of warm water appeared hundreds of miles off Alaska, British Columbia, Washington and Oregon that researchers called the “blob.” The water quickly moved toward land, stretching from Southeastern Alaska to Mexico.
But kelp prefers cooler temperatures. The blob, which dissipated by 2016, slowed the process of upwelling—in which cooler waters and nutrients move from deeper in the ocean up to the surface—choking off a critical supply of nourishment for kelp.
The loss of kelp has had immediate economic implications, including for two local fisheries. The region’s commercial red urchin fishery value fell from $3.6 million in 2013 to less than $600,000 in 2016, according to the New York Times. The recreational abalone fishery closed indefinitely last year. Both species depend on the kelp and were outcompeted by purple urchins.
The report highlights several tiers of recommended actions. The first tier includes the reduction of urchin populations through both commercial harvesting and recreational or volunteer-based efforts; the identification of areas of greater sea star population density and support for sea star reintroduction; and a pilot study to investigate culling urchins. The last recommendation given top priority was to sow kelp in decimated areas. The report suggested this happen within two years.
The second tier of actions included building up populations of sea otters, which have an appetite for urchins but remain threatened in California. Another second-tier recommended action was to investigate the feasibility, cost and scale of harvesting urchins with specially designed, remotely operated vehicles; current studies to do so are already underway in Tasmania and Norway, which face a similar dilemma.
Down the line, culturing kelp spores in a lab and planting them into areas cleared of urchins and other grazing pressures was recommended, as was transplanting sporophytes from wild populations of bull kelp forests to areas cleared of grazing pressure.
The report explicitly recommended against purposefully introducing a disease that would kill off urchins, genetically modifying urchins or establishing any type of artificial urchin barrier, which it disregarded as cost ineffective and infeasible.
Ms. Koe said the hope was that the report would provide the research necessary to prioritize projects for Fish and Wildlife and the sanctuary.
The recovery plan can be found at farallones.org/kelp.