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Scientists Seek Cause Of Fish Kill In Old Tampa Bay

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By MIKE SALINERO

The Tampa Tribune

Published: July 29, 2008

TAMPA - Wildlife scientists are trying to figure out what caused a fish kill that had motorists holding their noses as they drove across the Courtney Campbell Parkway in recent days.

Thousands of dead fish, mostly catfish and menhaden, lined the causeway from end to end when scientists with the state Fish and Wildlife Research Institute investigated Monday morning. People interviewed by the scientists said the fish kill happened late last week.

A second fish kill was reported Monday near Safety Harbor, just north of the causeway.

Scientists ruled out red tide, toxic marine algae that kills fish and marine mammals and causes respiratory distress in humans. Samples taken last week in Tampa Bay and other southwest Florida waters showed no red tide cells in the water.

Another algae with toxic properties could be involved. Pyrodinium bahamanse, a microscopic plant that discolors water much like red tide, has been in bloom in Old Tampa Bay since last week or earlier, said Cindy Heil, director of harmful algal bloom research at the institute.

Heil said the algae occur frequently in Old Tampa Bay, but usually not in such high concentrations as are being detected now. When large areas of what scientists call "biomass" accumulate in a waterway, they can deplete oxygen in the water during normal cell-building processes. Fish trapped in such an oxygen-scarce environment can't breathe.

"The water circulation in that part of the upper bay is not very good," Heil said. "It's calm, it's shallow, it's not well-flushed and you can get dissolved oxygen problems when there are that many [algal] cells around."

Although pyrodinium bahamanse produces a toxin, it usually builds up in shellfish and doesn't cause fish kills. Scientists with the state Department of Agriculture and Consumer Services recently sampled commercial shellfish beds at the mouth of Tampa Bay and found no evidence of the toxin, Heil said.

Two other, co-occurring species of algae, rhizosolenia and pseudo-nitzschia, could also have contributed to the fish kill, according to Theresa Cody, an assistant research scientist with the wildlife institute.

"They're really long and spiky," Cody said, "and they can get into the gills of the fish and cause problems. They won't be able to breathe as well if these things are caught in their gills in that high a number."

Heil said the cause of the fish kill may not be determined until the end of the week or later. She said she's sending a boat of scientists out Wednesday to collect more water samples from across the Bay.

"There are a variety of possibilities we're investigating," Heil said. "Sometimes you don't get an easy answer right away."

Reporter Mike Salinero can be reached at msalinero@tampatrib.com or (813) 259-8303.

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