Collapse of kelp forest imperils North Coast ocean ecosystem

“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.

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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.

Also factoring in the kelp die-off is the so-called “warm blob,” an area of persistent warm water that spread south from Alaska down the coast of North America beginning in 2014, upsetting the ocean’s rhythms and causing anomalies in the marine environment that have affected wildlife health, behavior and migratory patterns. The arrival of El Niño in 2015 reinforced the warm ocean conditions.

The shift deprived kelp of the normal upwelling of nutrient- rich cold water, which helps the seaweed grow as much as 10 inches in a day. In recent years, the kelp produced far fewer fronds, or blades, diminishing reproductive capability and making the seaweed more susceptible to dislodgement by heavy waves, Carr said.

The spike in urchin numbers and coinciding decline in kelp growth has led to a radically transformed near-shore underwater world that has shocked even veteran divers.

Surveys and reports have shown vast areas of kelp forest stripped of plant life by the purple urchins. Where normally they would hide out in crevices and feed on sea drift, they have emerged en masse and overtaken tidal zones, consuming whole kelp plants and whatever else they can find to eat, Carr said.

One fisherman described the underwater scene as “Urchintopia,” said Rogers-Bennett, a researcher with the state fish and wildlife department and the UC Davis Bodega Marine Laboratory.

Veteran diver Steve Lackey, an instructor at Sub-Surface Progression Dive Shop in Fort Bragg, said, “I try not to be an alarmist, but it is pretty unprecedented, in my opinion.”

This time of year, he’s accustomed to seeing small sprouts of kelp begin to appear on the ocean floor, a harbinger of the spring and summer growing season. This year, there are none, he said.

“I don’t remember quite this clean, this kind of scoured rock, with hungry invertebrates,” he said.

Toll on red abalone

The toll on red abalone has become clearer in just the past couple of weeks, Rogers-Bennett said.

The mollusks, prized by generations of hardy, wetsuit-clad sport anglers, compete for the same food sources as urchins. Of late, they also are exhibiting unusual behavior, leaving shelter in the rocks to climb denuded understory plants in an apparent search for kelp fronds to eat.

Surveys conducted last weekend at several active hunting sites north of Fort Ross on the Sonoma Coast turned up numerous examples of shrunken abalone among healthier specimens that had filled out their shiny iridescent shells.

One 18-year veteran of the sport fishery diving off Moat Creek near Point Arena on the Mendocino Coast said he was accustomed to seeing “fat boys” in the area and instead found only “skinny ones.”

A few miles north, off the Point Arena pier, many divers reported seeing empty shells of dead abalone, Rogers-Bennett said.

“We never see that,” she said.

Divers who venture into the sea for the larger, commercially prized red urchins, a species sought for its roe, or “uni,” also have observed signs of insufficient food for their catch.

Tom Trumper, an urchin diver and owner of Pacific Rim Seafoods in Fort Bragg, said a commercial diver usually will expect a harvested red urchin to yield about 7 percent of its mass in consumable uni, 10 percent if it is a really good one.

Right now, he’s catching urchin between 3 percent and 5 percent, and divers are having to go into deeper waters to get them, Trumper said.

Catton said the harvest and commecial value of red urchins has fallen by about two-thirds in the past two years.

“This is not due to disease, but due to starvation,” she said.

Key ecosystem

Kelp forests typically skirt the edge of North America, from Alaska to Baja California, and are considered among the most productive ecosystems on the planet.

Anchored atop rock reefs and layered like a terrestrial rain forest, they support a diverse array of wildlife and are even harvested commercially in some areas.

North of San Francisco Bay, the preeminent species is bull kelp, characterized by flexible stalks, or stipes, that resemble bull whips.

Fingered features called holdfasts allow the kelp to cling to rocks on the ocean floor and withstand the rough currents typical of the North Coast.

At the other end, each plant develops a spherical, buoy-like float filled with gas that helps keep the upper plant afloat, exposing fronds to the sunlight needed for growth.

Bull kelp can grow to 115 feet in length, creating towering wildlife habitat that buffers the force of the ocean.

Over the past two years, however, hardly any of the North Coast kelp is reaching the surface, Catton said.

Aerial surveys of the coastline from San Francisco to the Oregon border show that kelp forests now cover 93 percent less surface area than in past peak years such as 2008 and 1989, she said. Data from 2015 isn’t yet available.

Fort Bragg diver Jon Holcomb, a veteran red urchin fisherman, said the underwater transformation is dramatic.

Where the kelp forest was once thick enough to require divers to part the individual stalks to get through, it’s now “maybe 2 percent of what it was 20 or 30 years ago.”

He described seeing one narrow plant stalk covered 2 feet high in several inches of layered purple urchins “fighting to get the last of it.”

He’s also seen purple urchin gorging on overturned abalone and nibbling at their exposed tentacle fringe.

At Salt Point State Park on the Sonoma Coast, Gerstle Cove’s well-known kelp habitat is now “just solid urchin along the floor,” diver and state park lifeguard Joe Stoffers said.

“I mean, there was a dramatic shift between this last summer and the summer before,” he said. “There’s not much science behind what I’m saying, but it’s changed a lot.”

Seeking input

Marine scientists are still trying to get a handle on the situation, which came to light through routine surveys conducted largely to inform management of the abalone fisheries, Catton said.

They are reluctant to try to predict what they don’t yet know, and are looking for all the help they can get from divers and others with first-hand information about what they have noticed off-shore.

Catton and Rogers- Bennett have been reaching out to fellow scientists along the West Coast.

“We’re seeing this from sort of Central California all the way up into Oregon and Washington, so this is a very broad-scale impact,” Rogers-Bennett said. “It’s come about, we think, because of these multiple stressors on the system.”

Urchin barrens occur periodically in kelp forests, the result of disturbances in the food web that allow the invertebrates to overpopulate and, thus, overgraze a given area. The outbreaks are heavily studied and have yielded significant insight into the resilience of seaweed species, as well as restoration techniques.

But the kelp die-offs usually occur on a relatively small scale, in isolated areas or in more of a patchwork, Catton said. “They’re not hundreds of miles of coastline,” she said.

The scale of the current kelp collapse is what has scientists alarmed.

“You just don’t see the whole forest up and down the entire North Coast go away,” Carr said.

Bull kelp plants are a seasonal species that must re-establish itself each year in order to produce spores that bring about the next generation. With a third year of poor reproduction on the horizon, scientists aren’t sure how readily, if at all, the bull kelp can recover in the areas where it has disappeared. And if it does, can it survive the gauntlet of purple urchins?

“I think the big questions are: How long will these impacts linger?” Rogers-Bennett said. “Will this turn around? Or is this a new sort of stable state that will be with us for quite some time?”

Future unclear

The answer is unknown, and may depend in part on one’s perspective of time.

Bull kelp forests vary in size by season, and coverage is typically minimal at this time of year after the battering of winter storms.

But the species is built to recover, producing billions of spores that can persist in the ocean for some period of time before reproduction.

It’s like having a seed bank, said Jim Estes, a professor of ecology and evolutionary biology at UC Santa Cruz. “Having it all disappear would not be my big concern,” he said.

Exactly how long those seeds remain viable is unclear, however, and recolonization of such a vast area could be very slow, experts said.

“This species has been around for a while, since evolutionary times,” said Dan Reed, a UC Santa Barbara research biologist and deputy director of the Marine Science Institute. “There’s undoubtedly been times where these kind of constraints have happened, and it hasn’t disappeared. That’s not to say it won’t in the future.”

Catton is working to develop a pilot project that might test bull kelp’s resiliency through hand removal of purple urchins from small-scale areas. She met recently with several dozen red urchin divers and processors — people with the tools, know-how and motivation to help — and is hoping to move quickly to clear target areas to see if any of the seaweed springs up.

“The idea is to create little oases of kelp to see if we can,” she said.

Beyond that, researchers are in wait-and-see mode.

“Most kelps will recover if you give them space and time,” said Matthew Edwards, professor and vice chairman of biology at San Diego State University.

The abundance of purple urchins may only be solved through some other force, such as disease, predation or heavy storms, he said.

Otherwise, based on outcomes elsewhere, “you will lose species,” Edwards said. “You will lose biodiversity. And you will lose — or you’ll have reductions in — some of these commercial and recreationally important species. That’s pretty clear.”

You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.