At East Flower Garden reef about 100 miles off the coast of Texas, Emma Hickerson, sanctuary research coordinator for the Flower Garden Banks at the National Oceanic and Atmospheric Association (NOAA), descended into the depths of the Gulf of Mexico.
She saw something she had never seen before.
The water around Hickerson was green and hazy, with specs of white floating in it.
Something wasn’t right.
When she got to the reef, she found the corals, sponges and other invertebrate organisms dead or dying, covered in white bacterial mats and shedding their tissues in decay. When she went to collect samples of the dead organisms, they disintegrated in her hands.
“It was rather shocking,” she said. “Everything underneath the ledges of the corals were dead, the bivalves, the sponges, the algae, all the invertebrates — there was nothing living in that area, so whatever it was, it was very toxic and, to tell you the truth, we don’t know the cause.”
Hickerson’s initial visit to the devastated reef came on July 27 following reports of white mats, dead organisms and hazy green water, which came from a commercial diving vessel known as the M/V Fling.
The vessel discovered the die-off when it took divers to a dive spot at buoy number four, just 900 feet away.
After seeing the reef’s condition and collecting initial samples, the NOAA reached out to the research community. Researchers, including scientists and universities across the world, have been offering assistance.
Initially, two response cruises involving partners at Texas A&M, Rice University, UNC-Wilmington and UNC-Chapel Hill took place. Since then, partners such as USF have joined the research team.
So far, the cause of the event is still unknown, although many theories offer up links to freshwater or to a possible hypersaline event caused by the reef’s location atop domes of salt and minerals.
One such theory comes from USF marine biology professor Frank Muller-Karger. USF’s main source of data is from satellite images, which the university has records of dating back to the ‘70s and ‘80s.
His theory links the die-off to water coming in from the coastline and the Mississippi River, which may have pushed freshwater to the banks. The influx of freshwater shown in the satellite imagery was confirmed by research from Steve DiMarco and other Texas A&M researchers through water sampling.
“Especially in the last 17 years, we have not seen anything like this (in the satellite images),” Muller-Karger said.
While water quality sampling has provided useful information, it still hasn’t explained the reason behind the event or its localization. Biological samples are being collected and analyzed.
USF researchers are also out in the reef, in the water with teams from the sanctuary.
The East Flower Garden reef is part of the larger Flower Garden Banks sanctuary, which contains the West Flower Garden reef and several deep-water habitats. These deep-water habitats, as well as the west reef, were not affected by the die-off.
Current estimates based on the NOAA’s response to the mass mortality event estimate a 20 percent mortality of the reef’s coral cover, with up to 70 percent in some places within the 6.5 acres of affected reef.
No dead fish were found so the NOAA believes the fish have all but left the affected area, according to Hickerson, and many of the dead corals will not be able to recover.
“That’s the shocking part of it,” Hickerson said. “It was just a very immediate death to these organisms, and very localized.”
Another theory comes from Nancy Rabalais, distinguished research professor with the Louisiana Universities Marine Consortium, who thinks that freshwater from flooding in Texas — river flow from the Atchafalaya — and winds pushing water from west to east are the culprits, causing bottom water hypoxia, which means low oxygen levels in deeper water. She said she has seen phenomenon that would bring low oxygen to depths such as the Flower Garden Banks.
Her university hasn’t been involved in the research efforts, but involvement in the area is something Rabalais said she has been encouraging.
Muller-Karger said he isn’t too concerned about the incident at the reef spreading and affecting other nearby reefs. The satellite data is being monitored, especially as heavy rain continues to come down in Texas and Louisiana, but whether or not this will have effects on the reefs or other areas of the Gulf of Mexico can’t be said.
“It’s impossible to predict right now,” he said.
However, the uncertainty over a cause does leave Hickerson feeling uncomfortable about the possibility of the die-off spreading, but she said the dying seems to have stopped, with a few isolated areas being the exception.
“We’re crossing our fingers that that’s the case, that it has stopped and it’s not something like a pathogen that’s going to perpetuate across the reef or even be spread,” she said.
At first, the NOAA discouraged diving, fishing and other activities in the affected area, but Hickerson said as of now those advisories have been lifted.
The research currently being conducted is not scheduled to stop anytime soon, with Muller-Karger expecting USF to analyze and monitor satellite data dating back to the 1980s for the next two to three years. The effort to find an answer is important, Hickerson said, because this wasn’t an event like the bleaching that sometimes happens to reefs, so the effects are lasting.
“So right now we’re in the process of identifying funds and getting partners to collaborate with the processing of (collected) samples to … look at things like pathogens or any toxins or bacterial components that may give us an indication of what happened to these corals because the corals died,” Hickerson said.
This type of event is important, according to Rabalais, because the event may not be a one-time thing.
“We’re having more 500- and 1,000-year floods,” she said. “If that’s the direction of climate change for this area then freshwater influence and hypoxia may not be just a one-time event but may be — I wouldn’t say recurring — but more likely to happen in the future.”
Operating in a vast sea of uncertainties, the hope is to find the cause of the sudden and mysterious event that turned one of the healthiest reefs in the Gulf of Mexico into a coral graveyard sitting amid the green haze.