Marine Ecosystem Survey Encounters a New Variable: Falling Ash from Los Angeles Fires

The devastating fires in Los Angeles have numerous secondary effects as scientists are finding out now off the coast of Southern California.

Researchers from UC San Diego’s Scripps Institution of Oceanography and NOAA Fisheries’ Southwest Fisheries Science Center were collecting samples off the California Coast when the Palisades, Eaton and other fires broke out. The smoke that billowed from those fires dropped ash and debris that coated the ocean surface as much as 160 kilometers (100 miles) offshore.

The ship and its crew began collecting samples of the ash from the deck and the surrounding waters. NOAA has adjusted the ship’s course to make use of the chance to revisit the area to track any effects on the marine ecosystem. The survey is part of the collaborative California Cooperative Oceanic Fisheries Investigations (CalCOFI) program among the state of California, Scripps Oceanography and NOAA.

“We’re positioning ourselves to answer the question, ‘What does this mean for West Coast fisheries and the food web that we all depend on?’” said Nicolas Concha-Saiz, NOAA Fisheries’ chief scientist for the survey. The survey is being conducted aboard the NOAA Ship Reuben Lasker, which left San Diego Jan. 3.

While ash from wildfires frequently enters the ocean, the urban source of this fallout makes this a rare opportunity to sample ash from substances ranging from household chemicals to building materials. Scientists aboard R/V Reuben Lasker are collecting water samples to assess the spread of the ash. They will also monitor for toxics that could affect one of the country’s most productive marine ecosystems that supports important commercial and recreational fisheries.

Some crew switched out when R/V Lasker stopped in the Port of San Luis Obispo on Jan. 18. New crew members brought aboard additional, specialized equipment to capture and quantify the ash particles in the water, and preserve them for trace metal and other analyses. R/V Lasker returned over 48 hours to re-sample the most affected area, located in and just off Santa Monica Bay. Subsequent testing will look for traces of toxic materials in the tissue of organisms from plankton to larger fishes.

“These fires are not only consuming vegetation but also massive amounts of urban infrastructure,” said project leader Julie Dinasquet of Scripps Oceanography. “This introduces a novel ‘urban ash’ component to the wildfire source, filled with exceptionally toxic materials such as heavy metals like lead, arsenic, as well as asbestos fibers, polycyclic aromatic hydrocarbons (PAHs) and microplastics. These fires pose a potential significant threat to both humans and ecosystems through the introduction of a large amount of toxic material in the system.” 

CalCOFI has conducted quarterly cruises with few interruptions since 1949. The state, Scripps Oceanography and NOAA founded the program to understand why catches of one of the state's most prolific fisheries, sardines, diminished to almost nothing during World War II. The program sends vessels to designated locations in a grid off the California coast and repeats measurements of everything from the clarity of the seawater to the amount of fish eggs and larvae present. Researchers also collect water samples from selected depths for analysis of the water’s chemistry and other properties. The program has made coastal California one of the most extensively studied ocean regions in the world and its longevity provides a decades-long baseline of ocean conditions to which current conditions can be compared.

The science party aboard R/V Lasker included Scripps Oceanography biological oceanographer Rasmus Swalethorp, CalCOFI’s director of ship operations. The team knew about the fires from the news and could observe the large smoke plumes in the sky extending far offshore as they were nearing Catalina Island. They first observed ashfall during their transect from Dana Point to Santa Monica Bay on Jan. 8.  Ash and burnt debris were continuously observed into the next day when the vessel reached a sampling station past San Nicolas Island, some 100 miles offshore, and later in the south east of the Channel Islands National Park and off the coast of Ventura.

“Seeing it snowing, but knowing it wasn’t snow but ash was really eerie,” said Swalethorp. “It seemed apocalyptic. I can only imagine how it must have been on land.”

NOAA Fisheries’ scientists will watch for potential effects on fisheries and marine life, including anchovy eggs abundant in waters downwind of the fires. They have collected samples both before and after the eggs were exposed to ash and other debris, for any change in their number and distribution or any effects on their early development. 

“We have painstakingly saved archives of samples with treasure troves of information,” said Noelle Bowlin, NOAA Fisheries’ CalCOFI Director. “Any time there is a question, we can turn to the samples and see what changed.”

“What is most surprising to us is the size of the debris observed,” Dinasquet said. “There seems to be pieces of charred material up to five centimeters (two inches) long. We are sampling surface water but also deeper layers under 100 meters (330 feet) deep to see if we can observe sinking ash particles and how this material has changed and potentially leached toxics and other molecules as it sinks and how this will impact the ecosystem.”

The rapid response team performing the resampling brings together experts in the field of fire, marine and atmospheric sciences across the country to better understand the impact of these unprecedented fires. Additionally Scripps Oceanography PhD student Dante Capone will lead nearshore monitoring over the next few weeks as part of his work on wildfire impacts on California marine ecosystems.

Capone observed the impact of ash falling on Monterey Bay after the 2020 Lightning Fires. He and colleagues found that a group of algae called diatoms responded to what was likely an input of nutrients from the nearby fires in the Santa Cruz Mountains showing that ash from wilderness fires can act as a fertilizer. It could possibly show that the emissions and loss of one burnt ecosystem on land could be leveraged to fuel growth of another in the ocean, he said. 

“In contrast, given the source of the burn material in these Los Angeles fires, we are expecting much more ecotoxic effects,” Capone said.