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.
The cause of the bloom is unknown.
Islamorada-based backcountry fishing guide Ted Wilson said he noticed the bloom for approximately a month over the fall. But he said it didn't have a major impact on fishing, in part because it fell during the slow season.
"You get blooms every couple years," Wilson said. "I'd say on a scale of 1 to 10 on what I've seen over the last 20 years it was a 3."
But for the sponges of southwest Florida Bay, the bloom was apparently a disaster. Delgado said the loggerhead, variable and vase sponge species were among the hardest hit. A specific mortality estimate is not yet complete, but one will be forthcoming in approximately a month, and it should be relatively precise, he said.
That's because by coincidence the National Science Foundation was conducting sponge research in the southwest bay when the die-off took place. As a result, scientists have data that can tell them what the population was before the bloom. This week, the FWRI planned to collect date on the post-bloom sponge population in the area.
Sponges serve several functions within the Florida Bay ecosystem, including filtering the water of bacteria and nurturing small shrimp that live inside their internal organs. Their most prestigious role, however, is providing shelter for juvenile lobster.
Delgado said that during trips to monitor algae levels in the bloom vicinity it was easy to see that the absence of sponges was affecting lobster behavior. When he pulled monitoring equipment from the water it was crawling with lobsters.
"There was nowhere else for them to go," Delgado said.