News Press

November 9, 2014

 

Scientist say red tide fueled by 12 sources

By Chad Gillis

http://www.news-press.com/story/life/outdoors/2014/11/07/scientist-say-red-tide-fueled-sources/18661651/

Scientists studying red tide have identified a dozen nutrients sources that feed blooms, but they say no single source is responsible for the toxic outbreaks.

Red tide in Southwest Florida is caused by Karenia brevis, a single-celled organism that releases powerful neurotoxins that can cause mass fish and marine mammal kills, render shellfish inedible and cause respiratory issues in humans. Low concentrations of Karenia brevis have been documented in Southwest Florida in the past week and a report released Friday afternoon shows a bloom, mostly offshore, from Charlotte Harbor south to Marco Island.

Scientists hope this latest research will help them better track future blooms, which can harm the marine ecosystem and Florida's tourism industry.

Outbreaks have likely occurred for thousands of years and are a natural phenomena, but scientists haven't pinpointed exactly what causes Karenia brevis to go from normal to deadly levels. Upward of 236 manatees were killed in Lee County by a red tide outbreak in 2013. Causes of death for some animals were undetermined but thought to be related to the red tide bloom. It occurs throughout the Gulf of Mexico but is most problematic in Southwest Florida.

"One of the most interesting things that hadn't previously been taken into account is the organism's ability to not just use sunlight, like plants, but also consume other single-celled organisms as a nutrient source," researcher Judith O'Neil, a University of Maryland environmental sciences professor, wrote.

Other nutrient sources listed in the report include: bacteria transforming nitrogen in the water into more useful forms, decay of Trichodesmium blooms (identified as a long-term source) and nitrogen from the air.

"The things I hadn't heard about red tide consuming before were small phytoplankton other than Trichodesmium and Synechococcus," said Rick Bartleson, a water quality scientist at the Sanibel-Captiva Conservation Foundation. "The fact that they can consume organic matter was known, but what species they are consuming was not."

The Florida Fish and Wildlife Conservation Commission, the state agency that tracks red tide, reported Friday that low to medium concentrations were found at the north end of Captiva, Boca Grande Pass and the north end of Pine Island Sound and a large patch offshore of Bonita Beach, Naples and Marco Island.

Previously known sources include stormwater run-off, septic tanks, and excess nutrients from the upstream water management system, which starts south of Orlando and includes Lake Okeechobee.

The current bloom is mostly offshore of Lee and Collier County beaches and is 60 miles long and about 15 miles wide, FWC reports. Bartleson, who takes water quality samples at the Sanibel Causeway, Sanibel, Captiva and Pine Island Sound, said high concentrations were found last week in Pine Island Sound and at the Sanibel Causeway.

"It started offshore and came into the passes, like Redfish and Boca Grande," he said. "Concentrations are still higher in the north part of Pine Island Sound."

Bartleson said he wasn't surprised that red tide can subsist on a variety of nutrients, most of which are too small to be seen by the naked eye.

"I can see how they would discriminate based on particle size," Bartleson said. "It's not like they have brains and eyes to see what they're eating.

Connect with this reporter: ChadGillisNP on twitter.

Karenia brevis in cells per liter

 Background: 1,000 or less

 Very low: 1,000 to 10,000

 Low: 10,000 to 100,000

 Medium: 100,000 to 1 million

 High: 1 million and above

Source: Florida Fish and Wildlife Conservation Commission