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On August 2, as Damon Tighe was leaving the Oakland airport, he saw a dark channel in the bottom water forming near Alameda, an island in the eastern part of San Francisco Bay. At first, the community scientist thought it was an oil spill, but soon realized it was algae. He was still worried. If the algae turns into a harmful bloom that spreads in the bay, it can have disastrous consequences, Tighe knows. So, when he returned home, he kept an eye on her on his daily trips to monitor the bay’s shores.
By the end of August, Tighe’s worst fears had come true: The volume 10,000 fish came up on Lake Merritt, a tidal estuary in the heart of Oakland connected to San Francisco Bay. Tighe walked less than a mile around the lake on August 29, counting more than 522 striped bass, 39 bat rays, and tens of thousands of northern anchovies, topsmelt silversides, and yellowfin gobies—all dead. He quickly fixed one iNaturalist page for community members to document the “terrifying event,” and sightings of white sturgeon, dungeness crab, endangered green sturgeon, and other animals were soon reported as well.
Located due east across the bay from the Golden Gate Bridge, Lake Merritt’s 3.4-mile loop path is trafficked by thousands of walkers, runners, and bikers each day. “A good portion of the community is seeing lake life for the first time,” Tighe said, “but it’s only because it’s dying.”
The exact cause of the harmful algal boom, also known as red tide, remains unknown, but experts suspect rising water temperatures in the bay, more sunlight shining on the water’s surface, and an increase in Nutrient levels from water treatment plants contributed to size and bloom. severity. Stuart Siegel, interim director of the San Francisco Bay National Estuarine Research Reserve, called the bloom “absolutely extraordinary” in its extreme spread in San Francisco Bay, high number of fish kills, and rapid development. California Ocean Protection Council called the harmful algal bloom the “largest in recorded history” of the bay, with fish washing up dead on shore, but in the highest numbers in Lake Merritt.
Earlier in the summer, before the red tide and fish die off, a summer anchovy boom offshore provided plenty of food for the birds. Residents in the Bay Area are still eyewitnesses fish falling from the sky from feasting pelicans. “There are so many fish,” said Paige Fernandez, biologist at Richardson Bay Audubon Center and Sanctuary just north of San Francisco. Then, the algal bloom hit. This did not immediately damage the birds’ fish supply; in fact, the bloom made it easier to catch fish. At the end of August, the waterbirds enjoyed a all-you-can-eat buffet of fish and mollusks weakened by toxins created by algae, which do not seem to affect birds if ingested.
Now, Tighe and other experts worry that migrating birds to and from the Bay Area may experience the opposite phenomenon: a severe food shortage. “The bay is a major stopover on the Pacific Flyway,” Siegel said. If August’s red tide wipes out fish populations, migratory birds in desperate need of food could be in trouble. During peak migration, the Bay Area is over a million shorebirds and waterfowl there could be food shortages if fish cannot reproduce quickly enough to replace those lost in the red tide. “Now that all of those organisms are dead, I just don’t think [the populations] will come back in time,” Tighe said.
Shorebirds have started arriving, including the near-threatened Snowy Plovers and Ridgway’s Rails. Overwintering ducks, such as Surf Scoters and Greater Scaup, arrive in October and November. Hundreds of thousands of ducks converge in late winter to take advantage of the Pacific herring run—“the caviar of San Francisco Bay,” says Andrea Jones, director of bird conservation for the Audubon California. Good thing it’s early reports indicate that red tide may not hit herring as hard as other species. Anchovies, another fish commonly eaten by Bay Area birds, may be of greater concern. Tighe flagged the anchovy as a massive die-off when monitoring Lake Merritt and the bay’s shores. “I would be really concerned about the loss of the anchovy because so many birds depend on that fish,” Jones said.
Soon researchers will have a better sense of whether local fish populations are as depleted as they fear. If the birds arrive and the food is not what they expected, starvation events can occur. After a long migratory flight, many birds arrive in poor condition and need to refuel quickly, said Krysta Rogers, a senior environmental scientist at the California Department of Fish and Wildlife. “If there is no food when they arrive, they may or may not be able to travel to find food,” he said. Shorebirds and ducks also don’t have much choice in the area—their populations are stuck in the few remaining habitats in San Francisco Bay.
Lake Merritt, the first National Wildlife Refuge and home to more than 140 species of birds, is one of those residences. Tighe said he hasn’t seen an increase in starving or dead bird sightings since the iNaturalist page was created, but he has heard reports of missing Black-crowned Night-Herons and other commonly seen birds. in Lake Merritt. Whether their disappearance is due to red tide die-off is difficult to determine, but Tighe speculates it may be related.
“The red tide definitely affected the fish population,” Fernandez said. “Birds are possible [will] it’s harder to find fish to eat.” Even for non-threatened species, populations can suffer if a significant die-off event occurs. “In an extreme case, it’s possible we’ll see birds that wash up on beaches that starve to death,” he said. Tighe also worries about fish deaths from a recreational and human food safety perspective: Many non-native striped bass have died, which “caught by many families as a constant source of food around the bay.”
Researchers and officials are working to understand the causes of blooms and fish deaths. Experts say the fish die-off is likely driven by a drop in dissolved oxygen as the algae decomposes, a fish-killing toxin produced by the algae, or a combination of the two. The algae that cause the bloom, They say heterosigmais “a selective killer” that creates toxins in fin fish but is not known for moving up the food chain, said William Cochlan, who studies marine phytoplankton at San Francisco State’s Estuary and Ocean Science Center.
The San Francisco Bay Regional Water Quality Control Board is awaiting results for toxins in sampled fish in Lake Merritt. On August 29, they tested the water’s dissolved oxygen and found it had dropped to zero, likely due to its shallow water level, high nutrients, and limited water exchange. Algae thrives in shallow bodies of water that warm quickly and have little inflow of fresh water flowing in, Tighe said. Eileen White, executive officer for the board, said “we don’t think nutrients are the trigger [algal bloom].” But they allowed algae to grow and spread quickly.
Recently conditions have improved. The red tide has dissipated, and dissolved oxygen levels have returned to normal levels. Other than the missing fish wiped out by the bloom, White said “the bay is now back to its more normal state.” And so far, there have been no reports of dead birds, which community members can do do online.
The lack of these reports gives some hope that the worst-case scenario can be avoided during this transition. “We can make all these predictions, but sometimes fish populations bounce back and sometimes birds are a little more resilient than we give them credit for,” Fernandez said. “It’s hard to know exactly what’s going to happen before it happens.”
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