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Date of Issue: August 23, 2007

Red tide report: much work done, more needed

A comprehensive study of red tide that details the environmental, scientific, economic and social impacts of the water-borne problem has been released by Mote Marine Laboratory’s fledgling Marine Policy Institute.

In short, the assessment “calls for scientists, policymakers, stakeholders and the public to move beyond polarizing debate surround red tide research and focus on a more comprehensive red tide response strategy.”

“What we want to do is better connect science to society,” said MPI director Frank Alcock. He is a New College professor who joined with Mote last year to start the agency, which lists as its goal “to strengthen the scientific basis of public policy and societal decision-making for economic development and sustainability of our oceans and coastal ecosystems.”

But on to red tide.

In Southwest Florida, Karenia brevis is a type of plant that is always evident in the waters of the Gulf of Mexico and bays. At times, the plant “blooms,” and can cause fish kills, marine mammal deaths and harm to humans along the shore who breathe the itchy, scratchy, throat-irritating fumes of red tide.

As the report states, “Southwest Florida has endured red tide blooms on a near-annual basis over the past two decades, and the 2005 bloom was one of the most severe on record. However, Florida red tide blooms of similar intensity and duration have been confirmed as far back as 1948-49, and anecdotal evidence suggests that severe blooms have scourged the region for hundreds, if not thousands, of years.”

There has been some discussion of late regarding the impact of nutrient-rich stormwater runoff spurring the creation of red tides off the coast. The MPI report attempts to diffuse the discussion.

“Coastal pollution has been a focal point of contention between some scientists and stakeholder groups,” Alcock writes in his red tide assessment. “Some have expressed doubts over the importance of terrestrial nutrient sources in explaining red tide blooms, and others believe them to be a major contributing factor.... This debate, at times quite tense, can evolve into a more constructive dialogue as both sides better understand and acknowledge the reasons for contending viewpoints.”

The report continues by stating that, “Most scientists agree that red tide blooms initiate offshore before being transported inshore by wind and ocean currents. They express skepticism that terrestrial nutrients affect the early stages of a bloom. However, when a bloom moves inshore, most acknowledge that runoff can help maintain the life of a bloom or affect its growth.”

The assessment report then flatly states, “Florida needs to reduce nutrient loads to its watersheds for reasons that go beyond red tide, and it needs to develop a comprehensive management strategy for red tides that goes beyond reducing coastal pollution.”

Economic impacts

The “dollars-and-cents” hardship to coastal areas such as Anna Maria Island are not really quantifiable, the report states. In short, the figures widely vary.

One study quoted in the assessment report comes up with annual U.S. harmful algae blooms costing $82 million. The St. Petersburg/Clearwater Visitors and Area Convention Bureau pegged the financial hit in 2005 in that region alone at $240 million for the year-long outbreak.

As the report sums up the money loss, “The $240 million estimate of Tampa-area losses from the 2005 red tide event may be excessive, but the conservative averaged in the national [assessments] are likely too low.”

Health impacts

Red tide can make a day at the shore miserable for beachgoers. It can also be deadly for marine life.

Alcock explains that red tide produces a set of neurotoxins called brevetoxins. That chemical cocktail can kill fish, which can then create oxygen-deficient water, killing more marine life.

Red tide can also be deadly to marine mammals. In 1996, 149 manatees were killed by brevetoxins, Alcock reports. In 2004, 107 bottlenose dolphin deaths were reported after a red tide outbreak.

Shellfish, as filter feeders, can really pack in the toxic stuff, but survive. Humans, who eat the toxic oysters, clams or other shellfish, aren’t as lucky, but thanks to a quick response by state regulatory agencies in closing shellfish harvesting areas when a red tide is reported, no human ingestion problems have been reported.


So how can red tide outbreaks be stopped, or at least slowed?

The assessment report breaks it down into three elements, based on a National Oceanic and Atmospheric Administration plan:

“Preventive measures attempt to stop blooms from occurring, minimize their incidence or limit their extent. Control measures focus on limiting impacts by killing or neutralizing the toxicity of the causative organisms and/or removing the organisms and their toxins from the water column. Mitigation measures seek to limit the impact of the blooms without dealing directly with the causative organisms themselves.”

The report details a slew of possible measures to deal with red tide, many of which are successful elsewhere in the world, some of which could work here, all of which need further study.

To view a copy of the full report, go to, then to the science section of the Web page, then go to the Marine Policy Institute area and its report, “An Assessment of Florida Red Tide.”