Hurricane Harvey May Have Hurt the Gulf’s Already Stressed Coral Reefs

Coral reefs in the Gulf of Mexico that suffered losses in 2016 may face a new threat from the freshwater runoff that followed Hurricane Harvey, scientists who study the reefs warn.

The Flower Garden Banks, a protected reef off the coast of Texas, suffered a still-unexplained “mass mortality event” last summer. It also suffered from bleaching in high water temperatures in the fall. And data collected after Harvey may yield clues about last year’s event, said Adrienne Correa, a marine ecologist at Rice University.

Researchers at Texas universities sounded a new alarm after Harvey dumped 50 inches of rain on parts of Houston in late August, inundating the fourth-largest US city. Trillions of gallons of water flowed into the Gulf afterward, leading to a 10 percent drop in salinity in the water around the reefs, Correa told Seeker.

A hastily organized expedition found no evidence of a mass die-off, but some corals appeared to have unusual “blotchy” markings, she said. And the huge amount of fresh water still mixing with seawater along the Texas coast may pose a threat into November, she said.

“We didn’t immediately see an ocean floor of white or something that would indicate organisms were sloughing their tissue off en masse,” Correa said. “We did see some corals and sponges that sort of had slightly strange coloration patterns. So we sampled those, as well as organisms that appeared to completely healthy.”

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When the amount of salt in seawater falls below a certain point, coral tissues can swell and suffer damage. Fresher water could also introduce unfamiliar microbes into the reef ecosystem, or a layer of fresh water atop heavier salt water can prevent oxygen from reaching deeper water.

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Correa said new samples will be tested for microbial activity, proteins, and genetic markers to look for signs of damage that may not be fatal, but could stress or weaken the organisms. And scientists will be looking at the data for insights into last year’s losses, she said.

“We can look at all of this together in what appear to be healthy organisms and organisms that may have been stressed, and compare everything and see what exactly might cause a problem in this type of situation,” Correa said. “And we can also compare it back to the 2016 mortality event and see if there are any commonalities between those two.”

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In July 2016, recreational divers discovered a stretch of dead coral on the eastern portion of the reefs, which lie in a 56-square-mile national marine sanctuary. About 6 percent of the coral and thousands of marine creatures that lived among them were dead.

The find came three months after a wave of storms that dumped a foot and a half of rain on Houston in a single day. But cause was still under investigation when the reefs experienced bleaching in the fall, when water temperatures in the Gulf hovered around 30 degrees Celsius (86 degrees Fahrenheit), complicating the study. But Correa said that with new data, “We should be able to get much closer to an answer to that question.”

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