Red Tide "As Predictable as the Weather"
By Victoria Parsons
If a senior scientist with unlimited power had set the stage for showing human beings how little we know about red tide, he probably would have created scenarios like those we’ve seen off the west coast of Florida over the last two years.
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Photo courtesy Tampa Tribune.
Thousands of fish died last July when one of the worst red tide outbreaks in memory struck Tampa Bay.
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In 2005, one of the worst outbreaks ever began with visible blooms in early January, months before the traditional August to September season. Some researchers attributed the early and strong bloom to the four hurricanes that crisscrossed the state in 2004, dumping nearly twice as much rain as normal.
This year, blooms were minimal until late in the season, in spite of a record-setting number of hurricanes in 2005 and high levels of African dust in July, another anticipated boost for red tide. Then, just as the season should have been getting ready to settle down, red tide rebounded. “It’s about as predictable as the weather,” says Luiz Barbieri, head of marine fisheries research at the Florida Fish and Wildlife Research Institute. “There are so many factors involved that it’s difficult to predict much further than the very short term.”
Caused by the explosive growth of a tiny dinoflagellate named Karenia brevis in concentrations of up to 320 million phenomenon. Spanish explorers described “red waters” and the death of fish and birds in the 16th century. A 1947 outbreak nearly destroyed the commercial fishing industry and sponge beds near Tarpon Springs. The longest-ever red tide began in 1994, running two years before taking a brief break and returning in January 1996 with a bloom that stretched from Pinellas County to Key West and was blamed for the death of 238 manatees. Red tide has been present in the Gulf of Mexico annually since 1998, although the outbreaks range significantly in terms of size and intensity.
It affects almost every living creature, from fish, dolphins, birds, manatees, bottomdwelling benthos and human beings to other phytoplankton it crowds out as it bursts into a toxic monoculture.
A Front-Row Seat
Sue Barbieri has had a front-row seat on the devastating impact of red tide in Tampa Bay. A researcher specializing in spotted seatrout, she had been tracking the estuarine fish for the last five years. Last year should have been the culmination of those efforts. She and her team had a series of acoustic recorders in place at the most active spawning sites in the bay, and 31 male seatrout implanted with ultrasonic tags.
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The red tide outbreak in 2005 was so intense that it could be seen from the air, stretching from Key West north to Pasco County. Along with the visible victims that washed ashore, scientists and sportsmen report severe damage to both soft- and hard-bottom reefs offshore from Tarpon Springs to Sarasota. It appears that a layer of cooler water trapped the K. brevis cells on the bottom, killing benthic creatures including sponges, corals, worms, mollusks, crabs, sea urchins and starfish. A similar, but smaller, reef die-off occurred in the summer of 1971. FWRI researchers tracking that event reported that recolonization of reef fishes was seemingly complete within 18 to 24 months and that fish species composition was basically identical five years later.
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“Seatrout spend their whole lifecycle in the estuary and we were doing fisheries research, trying to learn where, when and how many fish were doing what,” she said. Although salmon are the only fish known to return to the spot they were born to spawn as adults, Barbieri was building a database that indicated seatrout may also have the same trait. “We were seeing male seatrout coming back repeatedly to the same site to spawn,” she said. Acoustic recorders in place since 2003 at a pass in lower Tampa Bay showed the expected increase as male fish returned to spawning sites last year beginning in mid-May.
“In June there were so many fish out there, we couldn’t differentiate them on the recorder,” she said. “By mid-July, we were down to two or three fish – it was like someone had turned off the sound.” All of the fish implanted with recorders – and tracked back to their favorite spawning site several times between May and early July – disappeared on July 14.
“It was a real shocker,” she said. “They were probably all killed because we never saw them again, even after the red tide receded and in spite of the fact that spawning season should have continued through September.
No one knows how long it will take for spotted seatrout populations in lower Tampa Bay to recover. This year started off so badly Barbieri’s team couldn’t catch enough fish to implant even after multiple tries with a gill net. In 2005, before the red tide struck, they caught an average of 10.6 fish per net set; this year, they caught 0.1 per run. When spawning season started in May, only a trickle of fish showed up in what was once Tampa Bay’s prime location. Then, about the time other fish discovered that the site was available and the acoustic recorders started sounding again, red tide came back too.
“One of the things we wished we had had last year was water samples, so we started sampling immediately,” she said. “Even at counts of 100,000 (K. brevis cells per liter), we were still catching some fish.”Wrong Place, Wrong TimeThe impact of red tide on different species clearly shows how important habitat is to fish populations. Seatrout and red drum – both members of the croaker family – were spawning in areas where red tide was concentrated. Snook, which tend to prefer lower-salinity waters, were only slightly affected as either adults or juveniles and adult sheepshead populations in Tampa Bay actually increased although juvenile counts declined sharply. “We saw massive mortality among the spotted seatrout and the red drum were hit pretty hard,” Luiz Barbieri said. “We’re very fortunate that the seatrout are likely to rebound quickly – generally speaking, the available habitat limits population growth.” But in upper Tampa Bay, where salinities are lower and red tide was not as concentrated, spotted seatrout populations only slightly declined. “Some fish were just in the wrong place at the wrong time,” Barbieri said.
More Questions Than Answers?
Like many natural phenomena, the more scientists learn, the more questions they raise – but answers may come soon. Florida already leads the world in red tide research with a forecasting system that combines data from multiple sources including images from commercial and government satellites, meteorological data from buoy- and land-based stations, and field data collected by state and university monitoring programs. For the first time ever, this year scientists had access to continuous, real-time information before, during and – eventually – after red tide conditions. Tests on potential methods to control red tide are currently focused on their overall impact in the ecosystem. “Lots of chemicals kill red tide, but it’s not always a good idea,” notes Richard Pierce, director of Mote Marine Laboratory’s Center for Ecotoxicity. For instance, copper sulfate was used to kill red tide in the 1940s. It worked, but it killed fish and birds too. Safer options being considered now include clay and ozone, but further work is necessary to ensure they don’t harm other animals. Constant monitoring also will be critical, he told a standing-room-only crowd at a seminar on red tide earlier this year. “The first satellite image we saw on January 9, 2005 showed a bloom about 40 miles long and 20 miles wide – about 800 square miles. A month later, it was 8,000 square miles.” If either clay or ozone prove to be effective at 1 part per million – about a teaspoon in a swimming pool – treating even the 800-square-mile bloom would require 8.4 million gallons and take 9.8 months to apply, he added.
An Ounce of Prevention
Preventing a natural phenomenon requires that scientists understand more about what causes it. Some believe that nutrients from stormwater have made outbreaks close to shore more frequent and intense, but others say that the data available now doesn’t support that theory. “There isn’t a smoking gun,” says Gabe Vargo, a biological oceanographer at the University of South Florida’s College of Marine Science. “It’s basic science that if you add nutrients to a system the biomass increases, but the evidence is very good that red tide starts offshore and is transported to shore.” The efforts to track those nutrients and measure their impact on red tide were boosted in October with a five-year $4.7 million grant from the National Oceanic and Atmospheric Administration. The new research, to be conducted by FWRI and Mote, will combine biological, chemical and physical measurements with predictive modeling efforts, as well as retrospective data analysis.
The new research may show that red tide starts offshore but that inshore nutrients fuel and maintain its growth once it gets close to land, Vargo adds. “If that’s the case, then there is something we can do about it. But we already know that nutrients in runoff cause algal blooms in many lakes and many people don’t seem to understand the impact of their actions. I sometimes wonder that if they truly understood what they’re doing — would they continue to do it?”
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The Role of African Dust
Luckily for Floridians, neither red tide nor hurricanes caused the havoc they could have created this summer. Ironically, African dust may play a role in both natural occurrences. A team of scientists working at the University of Wisconsin reported fewer hurricanes in years with higher levels of African dust – and dust in 2006 was among the highest ever recorded.
The same phenomenon, however, is more likely to increase the possibility of significant red tide outbreaks. Iron, a common component in the African dust, feeds the growth of a plant-like bacteria called Trichodesmium that ‘fixes’ nitrogen in the water making it biologically available to other organisms like K. brevis.
Sailors sometimes refer to Trichodesmium as sea sawdust, because it forms colonies that can be quite large and is visible to the naked eye. One theory is that blooms of Trichodesmium provide key nutrition that K. brevis needs to form its own bloom, but at this point, why Trichodesmium blooms occur and how they affect K. brevis is something scientists are still trying to understand.
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