DALLAS –  An eerie algae bloom that has painted chunks of Texas’ coast a reddish brown — and even a yellow-green in some places — has forced state health officials to ban oyster harvesting before the season officially begins.

The Department of State Health Services announced Wednesday that it was banning commercial and recreational harvesting of oysters, clams and mussels because the “red tide” algae bloom contains a toxin that can lead to shellfish poisoning in humans.

The algae boom, which is typically present along Texas’ coast beginning in September, is worse this year because of a historic drought and unprecedented heat. Already the algae, which thrive in warm, salty water, killed 3 million fish. It is the largest algae bloom in more than a decade along the Texas Gulf Coast, said Meredith Byrd, a Texas Parks and Wildlife marine biologist.

“We need a combination of rain and cold temperatures to start killing off the red tide,” Byrd said.

Texas’ oysters have already been hard hit by the drought, with 65 percent fewer market-size oysters than were seen at this time last year, according to the parks and wildlife department. the lack of rain has depleted the amount of freshwater in the estuaries, the conditions oysters most like to spawn in.

The low numbers will harm Texas’ $217 million-a-year commercial oyster industry. Texas and Louisiana make up 70 percent of the oysters found in the Gulf and the eastern seaboard. Louisiana has had almost no oyster harvesting this year because too much freshwater from Mississippi River flooding killed its harvest.

Christine Mann, a spokeswoman for the health department, the agency charged with protecting the integrity of Texas seafood, said the state is required by federal law to close down harvesting when red tide reaches at least 5 cells per milliliter.

“Red tide isn’t even visible at that point,” Mann said, explaining that a visible bloom is around 1,000 cells per milliliter. “So the threshold is very, very low.”

Texas’ oyster harvesting season normally runs from Nov. 1 through April 30. It is not yet known how long the ban will be in place.

Even when the waters clear, it may take quite a while for the oysters to detoxify, so the length of the closures will depend on how concentrated the red tide bloom was and for how long, Mann said.

The health agency will monitor the situation by taking water samples and testing the tissue of oysters.

A cold front expected to drop night temperatures along the Texas coast into the 50s is forecast for Thursday, but Byrd said it won’t be enough to “hammer away at the red tide” because the daytime highs will still be in the 70s and there’s no rain in the forecast.

To have an impact, water temperature needs to get below 60 degrees, Byrd said, and rain is necessary to help dilute the water so it’s not salty.

“I’m hopeful that over the next few weeks it (the algae) will start dying off, but I just can’t make that prediction,” Byrd said.

In the worst case in recent years, the hardest-hit areas of the bloom have seen it gone by Thanksgiving — but everything depends on the weather. the last red tide for Texas, from October 2009 through mid-February 2010, killed about 5.5 million fish, Byrd said.

“Unfortunately, it has really large impacts on the tourism industry,” Byrd said. “As you can imagine, people can be reluctant to go to beaches if they’re being hit by red tide.”

Families with children, particularly those with asthma or other lung disorders, should steer clear of the waters since the red tide toxin can become airborne and pose potential health problems. for healthy people it’s more of a nuisance that can cause coughing and sinus irritation — symptoms that go away as soon as an individual leaves the beach, authorities said.

tpwd.state.tx.us/landwater/water/environconcerns/hab/redtide/status.phtml