Near record ‘dead zone’ predicted for Gulf of Mexico. What’s that mean for red tide?

The National Oceanic Atmospheric Administration is predicting a near-record “dead zone” for the Gulf of Mexico this summer due to abnormally heavy rains in states across the Mississippi River watershed and the flooding that will ultimately spill hundreds of thousands of tons of nutrient-rich sediments into the Gulf.

The 2019 forecast is predicted to be 7,829 square miles — roughly the size of Massachusetts — where oxygen levels are expected to drop to levels unable to sustain marine life. It would be the biggest such area since 2017.

Scientists don’t believe 2017’s record dead zone had much to do with the onset that year of one of Florida’s longest and most intense blooms of red tide. The bloom started in October 2017 and by August 2018 was devastating beaches and inland waterways in Manatee County.

Cindy Heil, director of Mote Marine Laboratory’s new Red Tide Institute, said it isn’t likely NOAA’s forecast means red tide will return. Heil did say that the signs of what occurred in the Mississippi River are already showing up off the Manatee County shoreline.

“We just came back from off the water,” Heil said. “You can see where those nutrients are piling up but they are so salient at this point. I don’t believe the dead zone will have an effect on red tide along Southwest Florida. However, if [red tide] was to move up into the Panhandle, and then move west toward the dead zone, it could have an impact.”

Predictions of the dead zone are based on the annual U.S. Geological Survey of river flow and nutrient data.

This year’s prediction is for a dead zone larger than the five-year average. The dead zone — or hypoxic zone — is caused by excess nutrient pollution from the Mississippi River watershed, which flows into the Gulf.

NOAA nutrient map.jpg

The Gulf of Mexico, home to the world’s largest dead zone each year, is one of the only U.S. bodies of water that is not seeing a reduction in nutrient pollution runoff, according to Don Cline, associate director for the USGS Water Resources Mission Area.

“Long-term monitoring of the country’s streams and rivers by the USGS has shown that while nitrogen loading into some of the other coastal estuaries has been decreasing, that is not the case in the Gulf of the Mexico,” Cline said in a recent USGS report on the dead zone prediction.

What happens within the dead zone is the nutrients stimulate algae growth, the algae dies and then sinks to the bottom, lowering the amount of oxygen to levels below what is needed to support to marine life.

This past May’s deluge of rain across the Midwest led to discharges in the Mississippi and Atchafalaya rivers that were 67 percent above the long-term average.

USGS estimates the larger-than-average discharge carried 156,000 metric tons of phosphorus into the Gulf of Mexico in May alone.

Though Mote’s Red Tide Institute is fairly new, the effort to mitigate red tide is not.

Heil said the implementation of the institute is expediting that effort, “But we’re not there yet. We’re getting closer, but there is no single cure. What we do have is a toolbox growing with the number of tools we need.”

Heil said her research team has identified more than 13 different sources of nutrients that Karenia brevis — the organism responsible for red tide — uses as it forms offshore and moves toward the coast.

As to the nutrients that are capable of feeding and sustaining a prolonged outbreak, Heil said they also vary, depending on ocean conditions.

“So at any given time, looking at them is a complex endeavor,” she said. “Regardless, reducing human-contributed, near-shore nutrients should be implemented for the health of our environment and economy. This research might reduce red tide severity at the local level, but it is not expected to stop red tide entirely.”

Though many scientists agree that the blue-green algae released from Lake Okeechobee are certainly not helping the red tide situation on the coast, Heil said that organism — Microcystis — competes with Karenia brevis, and does not enhance it.

“However, our research suggests that a small part of last summer’s red tide bloom could have been supported by decay of the Microcystis bloom coming from the Caloosahatchee, which flows from Lake Okeechobee,” she said.

Heil said there is too much evidence that Lake Okeechobee’s flows don’t always correlate with bad years of red tide and don’t explain why the recent bloom was so, “lengthy and intense.”

Identifying which nutrients specifically could be playing a role in red tide is what Heil said her team is investigating, as well as how to kill it in the future.

Heil, who spoke Wednesday at a Manatee Chamber of Commerce meeting, said Mote has been experimenting on small levels with molecular, biological and chemical techniques that show promise for prevention when there are low concentrations. Scientists now have an understanding of where and how red tide forms in the Gulf and there is a legitimate possibility scientists one day can take the battle to red tide instead of the other way around.

Those methods include living reefs with filter feeding organisms at a red tide source. As to using other methods, Heil said, “So far we are testing 50 compounds and a lot of them can kill the algae, but only about 10 percent of those will also destroy the toxins, which is important.”

The utmost importance, Heil said, is to continue to determine which method, or combination of methods, “will not do further harm to the ecosystem than what red tide has already done.”