The closures come after DSHS crews found elevated levels of the Dinophysis organism entering the Texas bays from offshore waters, indicating a bloom is occurring where Texas oysters are harvested. A bloom can occur when microscopic algae grow quickly in water, forming visible patches. DSHS officials say they know of no health issues associated with people being in water containing the algae.
The toxin produced by Dinophysis, okadaic acid, can accumulate rapidly in shellfish tissue and cause diarrheic shellfish poisoning, or DSP, in people who consume oysters, clams or mussels. DSP symptoms include vomiting, diarrhea, nausea and cramping. DSP is not life threatening and does not generally cause long-term effects. DSHS is not aware of any illnesses associated with this bloom.
Texas shellfish harvested before today's closure do not pose an elevated health risk. Cooking does not destroy the toxin. The toxin does not affect other seafood, such as shrimp and crab.
"Temporarily closing the waters to harvesters is a preventive but necessary measure," said Kirk Wiles, manager of the DSHS Seafood and Aquatic Life Group. "Historically, this organism has produced toxin in Texas oysters that can cause illness if the oysters are consumed."
In 2008, a bloom of Dinophysis produced toxin in oysters and required DSHS to close several bays on the middle Texas coast.
DSHS will continue to monitor the movement of the organism. Oyster tissue will be tested to determine when safe harvesting can resume. The area will remain closed to harvesting until further notice from DSHS.
Dinophysis occurs naturally in ocean waters and estuaries. Typically it is not found in high numbers along the Texas Gulf Coast.
The public oyster season ends April 30 in Texas. If no closure is in effect, oyster harvesting is allowed year round on private oyster leases in Galveston Bay. Harvesters should check the status of harvest areas by calling DSHS at 800-685-0361.