Researchers have detected large blooms of toxin-producing algae in Monterey Bay that appear to be poisoning marine mammals and seabirds. Blooms of the algae, which produce a neurotoxin called domoic acid, first appeared in southern California earlier this spring and are now occurring along the Central Coast.

Researchers throughout the Monterey Bay region have been monitoring the situation closely and have detected high levels of the toxin in the bay. Meanwhile, large numbers of dead seabirds, as well as sea lions with symptoms of domoic acid poisoning, have been turning up on Monterey Bay beaches. The link between seabird deaths and domoic acid poisoning is difficult to make, however, and researchers are still analyzing data and waiting for definitive test results.

"The impact on marine life depends on how much of the toxin gets into the food web, but in terms of toxin production and the size of the bloom this event is similar to the large blooms we saw in Monterey Bay in 2000 and 2002," said Raphael Kudela, Associate Professor of Ocean Sciences at the University of California, Santa Cruz.

At the same time, harmless blooms of "red tide" algae have turned the water a reddish-brown color in parts of Monterey Bay. These organisms, a type of dinoflagellate in the genus Ceratium, do not produce toxins.

Domoic acid is produced by diatoms (a type of single-celled algae) in the genus Pseudo-nitzschia. A potent neurotoxin, domoic acid accumulates in shellfish and fish that feed on the algae, such as anchovies and sardines. . . [S]eabirds and marine mammals can suffer massive die-offs during this kind of harmful algal bloom.

In Southern California, hundreds of seabirds and marine mammals have died from domoic acid poisoning this spring. The domoic acid levels there have been much higher than those detected so far in Monterey Bay--a mussel from Santa Barbara had the highest domoic acid level ever detected. Large numbers of marine animals have been affected, including dolphins and other cetaceans.

"It's not a single, uniform event--the blooms are spotty, both in time and in locations throughout the bay," said Mary Silver, Professor of Ocean Sciences at UCSC. "When you look at satellite images, the blooms are almost like weather systems or cloud formations--they come and go on a day-to-day basis. But the animals are being affected."

James Harvey, a Center for Integrated Marine Technologies (CIMT) collaborator at Moss Landing Marine Laboratories (MLML), said California sea lions are the marine mammal species most affected by domoic acid, because they are plentiful along the coast and feed heavily on anchovies and other fish that accumulate the toxin. He said the current harmful algal blooms may end up killing hundreds of California sea lions, but the increased mortality will not have a significant impact on their population, which is currently around 160,000 to 180,000.

"It's hard to assess the numbers, because all we see are the ones that wash up on the beach. For Southern California, the numbers on the beach are definitely elevated this year," Harvey said. "The numbers locally are not that unusual, but we have seen sea lions with symptoms of domoic acid poisoning."

Melissa Miller, a veterinary pathologist at the California Department of Fish and Game's Marine Wildlife Veterinary Care and Research Center, reported that dead sea otters found in the Santa Cruz area this spring showed signs supportive of domoic acid poisoning.

Two dead whales also washed up on area beaches this spring, but their deaths were probably unrelated to domoic acid, said Donald Croll, associate professor of ecology and evolutionary biology at UCSC. "This is the time of year when the females and calves are moving north to their feeding grounds, and there is typically some mortality along the way," he said.

CIMT coordinates with the monitoring programs of the Monterey Bay National Marine Sanctuary, such as Beach COMBERS, a sanctuary and MLML volunteer program that conducts regular surveys for marine birds and mammals on the beaches. Although the numbers of dead birds on the beaches are higher than normal this spring, it is not yet clear whether domoic acid poisoning is responsible. The Beach COMBERS reported a large die-off of common murres in Monterey Bay in February and March that appeared to be the result of poor prey availability.

Elizabeth Phillips of the Department of Fish and Game's Marine Wildlife Veterinary Care and Research Center said, "There are a lot of factors at play in the seabird mortalities we've seen lately, and it is difficult to determine whether the increased mortality is related to a domoic acid event or a combination of mortality factors."

CIMT surveys indicate that krill, the small crustaceans that are a favorite food for many seabirds, are currently abundant in Monterey Bay. But the krill may be contaminated with domoic acid.

Upwelling of cold, nutrient-rich water along the coast, driven by winds that push the warm surface layer offshore, determines the productivity of the Monterey Bay ecosystem. The influx of nutrients sparks blooms of algae, which feed krill and small fish that are, in turn, prey for larger fish, seabirds, and marine mammals. Why the algal blooms are dominated by toxin-producing algae in some years is one of the questions researchers are trying to answer. This is a natural phenomenon, however, and will subside as conditions change in the bay.