Dead and dying scallops began washing up by the thousands in Sanibel last week along with sponges, clams and starfish.
Scientists do not believe red tide or low oxygen levels in the water, the two usual suspects, caused the scallop die-off, said Wendy Quigley, spokeswoman for the Florida Fish and Wildlife Research Institute. Scientists with the institute took oxygen readings Thursday in the Caloosahatchee River and around Sanibel beach but found normal levels, Quigley said. They also found no high levels of Karina brevis, the organism that causes red tide, she said.
"The two suspect causes that would come up at first don't appear to be the cause, but we're still investigating," Quigley said.
Rick Bartleson, a scientist for the Sanibel-Captiva Conservation Foundation, said he first noticed scallops washing up in November. Samples he sent to the institute at that time showed elevated levels of the red tide toxin.
He started noticing them again last week, numbering up to 100 per squaremeter, Bartleson said. "It's pretty impressive just to see that many," he said. "Some of them are still alive when they wash up, too."
Oxygen is likely not a problem in the winter because cool water holds higher oxygen levels, Bartleson said. If it's not red tide, it could be some other toxin, he said. Scallops are very good indicators of toxic algae blooms because they filter water to eat. "If something toxic is killing them, then people should know about it because you wouldn't want them picking them up and taking them home and eating them," Bartleson said.
In July, the Lee County Health Department declared an epidemic after 11 people were diagnosed with neurological shellfish poisoning after harvesting and eating shellfish from local waters.
Doctors hospitalized six of the victims, four of whom needed intensive care, with symptoms including dizziness, difficulty walking, nausea, vomiting, diarrhea and prickling or tingling of the skin. The victims recovered after the toxin cleared their system.
All of the victims were from out of town and got sick after collecting the shellfish in waist-deep water in the Gulf of Mexico just off the beach. The practice of collecting shellfish without a permit in Lee County is illegal.
Ten of the 11 cases came from Sanibel and one originated in Fort Myers Beach. At the time, the county, the city of Sanibel and the Lee County Visitor and Convention Bureau issued warnings and tried to alert tourists of the problem.
If there is a reason for concern, the Florida Fish and Wildlife Research Institute will notify the Department of Agriculture and Consumer Services, which would then alert local communities, Quigley said.