TradeEdge-On California’s Coast, Black Abalone, Already Vulnerable to Climate Change, are Increasingly Threatened by Wildfire

BIG SUR,TradeEdge Calif.— It’s four in the morning, damp and dark along the central California coast. Huddled around the back of a minivan, five scientists in waders and boots tenderly move 41 black abalone from large white coolers into reusable Trader Joe’s grocery totes lined with wet, cold washcloths and ice packs. 

With abalone slung over their shoulders, they hike towards a field of jagged, slick boulders, beams of light bobbing from their headlamps.  The team is working at the mercy of low tides, which meant a 1 a.m. start to their day, but the morning’s early negative tide will help them return rescued abalone into the wild.

In February, Wendy Bragg, a marine ecologist and doctoral student at the University of California, Santa Cruz, along with other scientists from Multi-Agency Rocky Intertidal Network or MARINe, retrieved 200 endangered black abalone from areas along Big Sur’s coast. Heavy rain had washed over land scarred by California’s worst fire season on record, creating large debris flows that barreled off cliffs and slammed into rocky intertidal habitat. The landslides buried some black abalone alive and destroyed rocky shoreline preferred by the marine snail, which is endemic to California and Mexico. 

An arsonist is believed to have caused the Dolan Fire that scorched Big Sur, but Bragg, who has a background in fire ecology, believes black abalone, a species already vulnerable to disease, warming ocean waters and ocean acidification, may face increasing threats related to fire.

“As climates are changing, we know fires are increasing,” she said. “We know the intensity is increasing. If you think about just the terrestrial system, it’s obvious fires affect that,” Bragg said. “We now know it impacts the intertidal system.” (California’s current fire season is outpacing the historic summer and fall of 2020.)

Big Sur’s majestic, steep cliffs are prone to landslides, fires or not. The contour of the coastline beneath these slopes bends and meanders for more than 100 miles. About 70 percent of the state’s healthy, reproducing black abalone population live along this stretch of coast in the intertidal zone. Black abalone, known for the dark outer shell that boasts a glimmering, pearly underside, is the only abalone species that does not need to live submerged in water. 

Last fall, Bragg watched the Dolan Fire burn along Big Sur and knew debris flows would follow if winter brought intense rainstorms. In coordination with the National Marine Fisheries Service and the California Department of Fish and Wildlife, she started planning a rescue operation. MARINe had extensive documentation of where black abalone resided, and Bragg conducted her own surveys. After the landslides struck, she returned to several sites, some of which were unrecognizable.  

“When you think of a debris flow, you think of flowing sediment,” Bragg said. “But it really did explode. We found minivan-sized boulders had moved, pieces of cliff were sheared off of bedrock. We found abalone with completely scoured shells and scoured tissue. We had one area, where the water is beginning to wash away some of the heavy cement-like sediment, and we found 200 empty shells. So we know we’ve seen a lot of losses.”

Forty years ago, black abalone were so prevalent in southern California there wasn’t enough real estate. They’d cover rocks, then stack on top of each other like stones. But starting in the mid-1980s, overharvesting followed by withering syndrome, a disease in which abalone grow weak, starve and die, caused mass mortalities, wiping out the southern California population by 80 to 90 percent. Commercial and recreational harvesting became illegal in 1993, but withering syndrome continued to spread up the coast into central California. The species was listed as endangered in 2009. (Of seven abalone species, white and black are endangered). 

Bragg says rebounding black abalone populations isn’t easy. They’re broadcast spawners, meaning egg and sperm must meet in the water column. A sparse number of black abalone located several meters apart won’t get the job done. “So populations can keep decreasing,” she said. 

On that early Sunday morning, Bragg and her team crawled up and over boulders, then bent low or lay flat to shine flashlights into cracks and crevices. They were eager to find  “resident” abalone that the transplants could join, not only for reproductive purposes but native abalone is a signal that the site is “pre-approved,” said Bragg, and probably good, safe habitat full of the algae and drift kelp that black abalone eat. 

Pete Raimondi, a UC Santa Cruz professor of ecology and evolutionary biology who leads the black abalone rescue and release project in Big Sur, said it’s still unclear how much of the Big Sur coastline was damaged. And they’re still researching how many black abalone are likely to have died as a result of landslides. Using drone imagery and remote sensing to see where sediment collided with the shore, and how it then dispersed, Raimondi said he’s confident that not all black abalone habitat along Big Sur was affected, but, “it’s way worse than any of us expected.” 

That has made finding suitable habitat to rehome rescued black abalone difficult. Scientists need intertidal areas that are accessible on foot, but not so easy to reach that poachers might show up. And Raimondi said they wanted to avoid areas adjacent to the Dolan Fire’s footprint. Last year’s rain was confined to one large storm, and the rest of the rainfall was not enough to stimulate the kind of vegetation growth needed to stabilize soil. “What we’re worried about is another big rain event,” he said. “If we get a big rain year, landslides are going to be another issue.” 

Standing on rocks and sprinkled with the mist from crashing waves, Bragg gently pulled black abalone one by one from individual mesh bags and handed them to her team. Several of the animals emerged with tentacles wiggling and their single, muscular foot swiveling clockwise, then counter-clockwise. 

“What it’s doing is it’s feeling around so that it will attach itself to something,” Bragg explained, before one of the abalone suctioned itself to her palm. Each abalone is numbered and marked with colored spots on its shells, allowing Bragg to easily identify and monitor how it fares in its new home. Each boulder the abalone attaches to is numbered and named—Cookie, Camel, etc.—and its location recorded in GPS coordinates and photographs. 

In total, over the course of a week, the team will return about 140 rescued abalone to the Big Sur coast, with a few more releases scheduled for the end of the month. Bragg says 40 had died in captivity, largely because of trauma sustained at the time of the debris flows. 

“When you actually get to put them in place and they attach it’s really a wonderful feeling because we rescued them from someplace where they were basically the walking dead,” she said. “And so any one that survives at this point is a positive. And seeing them attached and cruising off to where the residents are is a great feeling.”

Still, many other challenges face black abalone. Withering syndrome has faded over the last several years, but Raimondi said that if waters continue to warm, “it’s very likely that there will be repeats of (the disease) in populations.”  

Ocean acidification is another emerging threat that could hinder normal growth, development, and survival of abalone by altering pH levels, lowering the availability of calcium carbonate, which affects abalone shell formation, and makes it more energetically taxing to add shell growth.  Reduced carbonate availability also reduces crustose coralline algae that juvenile black abalone depend on for habitat. 

This summer, as Bragg and her team scale boulders to relocate abalone, salmon are being trucked to the Pacific because of the drought. In Canada, millions of mussels and other tidal creatures baked during a recent extraordinary heat wave. Bragg said each event points to a stressed, warming planet. 

“In ecology things are connected. I do think you’re going to start seeing more of these impacts,” Bragg said. “While we could continue on a path of rescue and relocate after severe events have impacted a population, this is a losing game. The large losses of the original impact are not isolated. Additional mortality can and does occur throughout the rescue process. My hope is that we start to go back to those causes, and try to change those rather than trying to rescue or remediate the impacts we’re seeing.”