SACRAMENTO — The grim outlook for California’s beloved Dungeness crab got bleaker Thursday when the state Fish and Game Commission took the unprecedented step of delaying the recreational crab fishing season for up to six months because of a public health threat.

The Fish and Wildlife Department is expected to institute a similar closure for the much larger commercial fishery by next week, which would exact a high financial toll on Bay Area fishermen and prevent consumers from enjoying Thanksgiving feasts of fresh local crab.

Sonke Mastrup, the commission’s executive director, said the delay to the recreational season will likely be far less than 180 days. The unusually large and persistent algae blooms responsible for the crisis should begin to die off as the days get shorter, the weather gets colder and ocean temperatures dive toward their winter lows.

The blooms have already begun to decline, according to the state Department of Public Health.

“I’m kind of hoping as testing progresses we see this disappear in the next few weeks,” Mastrup said after Thursday morning’s emergency meeting. “But who knows? We can’t say for sure.”

The state Office of Environmental Health Hazard Assessment recommended the closures after tests by the Department of Public Health revealed high levels of domoic acid in the meat and viscera, or “butter,” of crabs up and down the coast. The acid is a potent neurotoxin caused by harmful algae blooms that have proliferated this year in the unusually warm waters off the Pacific coast.

Charter boat operators will suffer from the delay to the recreational season as much as anyone. Tom Mattusch, who operates the Huli Cat out of Pillar Point Harbor in San Mateo County, said he’s had $10,000 in cancellations over the past few days.

“I was booked every day through November,” said Mattusch, estimating he’ll miss out on roughly $40,000 in sales this month. He’ll make much of that back once the season begins, but not all of it.

“A day lost is a day lost. You never get that day back,” he said. “Everybody’s just totally on hold, hoping and praying that something opens soon.”

The Fish and Game Commission also voted Thursday to close the recreational rock crab fishery, which is open year-round. The closures are in effect from the Oregon border to the southern boundary of Santa Barbara County, where most of the state’s crab fishing occurs.

Charlton Bonham, director of Fish and Wildlife, will decide whether to postpone the commercial Dungeness and rock crab seasons. The commercial Dungeness crab season is slated to open Nov. 15, while the recreational season was supposed to begin Saturday.

Tests by the Public Health Department show levels of domoic acid in crabs that exceed federal safety limits of 20 parts per million in the meat and 30 ppm in the viscera. Test results varied by region and specimen. The highest level recorded was 190 ppm in a yellow rock crab in the Monterey region. Crabs with acid levels of 120 ppm or higher were caught in four other regions, including the San Francisco-Half Moon Bay area.

Olga Pulido, a researcher at the University of Ottawa who has studied domoic acid, said the levels are high enough to cause serious illness.

“The values that they found are high,” she said, “and it was a very good idea to issue a moratorium.”

Domoic acid poisoning, also known as amnesic shellfish poisoning, may cause vomiting, stomach cramps, diarrhea and other symptoms in mild cases. Severe intoxication may cause permanent memory loss and even death.

The first reported case of domoic acid poisoning occurred in 1987 on Prince Edward Island in Canada. Three people died and more than 100 were sickened. No deaths or illnesses from domoic acid have ever been documented in California, according to the Department of Public Health.

As conditions improve, the Fish and Game Commission will likely reopen the ocean to recreational crab fishing county by county as test results determine that crabs in various regions are safe to eat. The commission will post a list of the areas that are closed on its website — www.fgc.ca.gov — and update the list once a week on Wednesdays.

Ocean temperatures off the Central Coast have been between 2 and 9 degrees higher than average this summer and fall, according to Nate Mantua, a Santa Cruz-based research scientist with the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center.

Temperatures in some spots along the coast dropped a couple degrees this week in response to northwest winds, but the water could warm back up depending on wind patterns, Mantua said. The ocean will likely remain warmer than historical averages throughout the winter, he said.

Mantua said the spike in coastal ocean temperatures since 2014 may have begun in Baja California, where weak winds allowed waters there to warm. Other scientists point to “the Blob,” a mass of warmer than normal water farther out in the Pacific Ocean.

Marc Gorelnik, chairman of the Coastside Fishing Club, said his group is disappointed by the delay of the recreational season but understands the need for it.

“No one wants to see anyone get sick,” said Gorelnik, whose club represents about 10,000 recreational anglers, mostly in the Bay Area. “It will take some time for the acid to work its way out of the crabs. We’ll just have to wait and see how long that takes.”

Contact Aaron Kinney at 650-348-4357. Follow him at Twitter.com/kinneytimes.