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SOUTH FLORIDA — A blue-green algae bloom caused a sponge die-off in a portion of southwest Florida Bay over the fall and winter.

"All the large sponges died, the ones larger than five inches," said Gabe Delgado, an assistant research scientist based at the Florida Fish and Wildlife Conservation Commission's Marathon office. "Probably thousands into the tens of thousands."

Scientists with FWC's Fish and Wildlife Research Institute are still analyzing water samples from the bloom. But it was at its most intense in September and October, according to Delgado.

Data mapping provided by the research institute shows that around that peak time the bloom was centered in Rabbit Key Basin. There the chlorophyll levels, which indicate algal buildup, were 15 times normal. The bloom extended close to 10 miles in every direction with its intensity, for the most part, gradually decreasing. Read more at