Energy & Environment

Flooding From Hurricane Harvey Polluted Coral Reefs More Than 100 Miles Offshore

The research shows just how far Houston’s flooding problems go.

Flower Garden Banks - NOAA
An abundance of sea life inhabits the Flower Garden Banks National Marine Sanctuary. Researchers found pollution from flood runoff reached the marine sanctuary.

Flooding from major storms like Hurricane Harvey polluted coral reefs more than 100 miles offshore, according to a new study by researchers at local universities, including Rice and Texas A&M.

"Those are not the reefs that we typically would think are in danger of being affected by floodwaters from the land," said Rice University researcher Adrienne Correa. "It was a big surprise."

Recreational divers were the first to notice that something was wrong a few months after Houston's 2016 Tax Day Flood, during which 240 billion gallons of rainwater fell on Harris County, Correa said.

The divers were at the Flower Garden Banks National Marine Sanctuary, which is known for its clear waters and colorful coral reefs. But they said when they arrived, the water was murky and green.

"They saw that organisms had this white bacterial matte on top of them and they were just disintegrating," Correa said. "Sponges were falling apart, corals were falling apart, fish were swimming away, and lobsters were doing things like climbing on top of coral colonies where you don't usually see them."

Correa said about 80% of the corals and organisms in the area were dying.

The team of researchers then took samples of sponges, which act as natural water filters, and found bacteria from human wastewater.

Giant barrel sponges were studied by marine biologists investigating the impact of extreme storms on coral reefs in the Flower Garden Banks National Marine Sanctuary.

"That was when we made this initial jolting connection that floodwaters could make it out that far," she said.

They found the same thing again after Hurricane Harvey, during which upwards of 31 million gallons of raw sewage spilled across southeast Texas.

"We were able to see bacteria associated with human feces out on the reef in sponges that were 60 feet below, on the bottom of the seafloor," she said.

The Flower Garden Banks National Marine Sanctuary recently tripled in size to protect an additional 14 reefs. The sanctuary is an important marine habitat for a range of species, including threatened or endangered manta rays, sea turtles and corals.

Marine life at Flower Garden Banks was less impacted during Hurricane Harvey than during the Tax Day Flood. That’s because ocean currents carried more of the pollution down the coast instead, Correa said.

The team also took samples of sponges during years without major flood events for comparison and didn't find fecal bacteria then.

Previously, research has been focused on the impact of floodwaters on ecosystems closer to shore. A study by the Galveston Bay Dolphin Research Program, for example, found that dolphins in upper Galveston Bay developed skin lesions after flooding from Hurricane Harvey impacted water quality.

Correa said given that climate change is increasing the intensity of storms, it worries her that polluted floodwaters can reach marine areas farther away than previously thought.

"There is the potential that we could have more flooding and more significant runoff events, leading to problems out on the reef," she said.

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