Texas Treasure Threatened
Whenever something happens in the Gulf of Mexico, people ask Flower Garden Banks National Marine Sanctuary director G.P. Schmahl whether it will affect the Gulf’s coral reefs. Dubbed the “Texas Caribbean” by scuba divers and anglers, the sanctuary’s three sections — the East, West and Stetson banks — protect coral reefs growing atop geologic formations called salt domes near the edge of the continental shelf.
So far, thanks to the sanctuary’s location (roughly 100 miles from the Texas coast), Schmahl usually answers “No.” But coral reefs worldwide face serious threats, some that affect even the Flower Gardens.
“Increase in water temperature is probably one of the biggest impacts in the long term,” Schmahl says. At temperatures above 86 degrees, many species of coral expel their symbiotic algae, which leaves them looking white, a condition known as bleaching. Without food the algae produce by photosynthesis, corals can starve; loss of coral reverberates throughout a reef system.
In 2005, 45 percent of Flower Gardens corals bleached, says sanctuary research coordinator Emma Hickerson, and in 2012, bleaching affected some 7 percent. In October 2016, 46 percent of corals in a study site at the East Bank bleached or paled, an early stage in the process of bleaching. Fortunately, most recovered, with slightly less than 4 percent dying.
Bleaching isn’t the only thing affecting the corals, though. In July 2016, on an area of the East Bank, scientists found dead and dying corals, sea urchins, clams and small crustaceans — essentially anything that couldn’t swim away, says research ecologist Michelle Johnston.
Scientists from the sanctuary and a half-dozen universities stepped up efforts to try to figure out what caused the event. While still crunching numbers, they gathered in February to compare notes. Most agreed that, based on existing data, a low level of dissolved oxygen in waters around the reef was the most likely contributing cause.
One hypothesis suggests that the localized low oxygen resulted from a combination of warmer water, layering of freshwater and saltwater from unusually high levels of river water entering the Gulf, and an algae bloom followed by bacteria feeding on the dying algae, consuming significant amounts of available oxygen in the process. Sanctuary scientists believe the event probably resulted from a combination of these stressors, rather than a single cause.
Increasing fishing intensity throughout the Gulf, and beyond, threatens these reefs as well.
“There is little evidence of a negative impact related to that so far, but over the long term, removing high-level predators such as sharks and groupers from the marine ecosystem in general does have an effect,” Schmahl explains. These predators help maintain the balance of various sizes of fish, ensuring, for example, that algae doesn’t take over a reef.
Another threat comes from land: Two-thirds of the U.S. along with parts of Canada, Mexico and Cuba drain into the Gulf. Runoff from cities, industry and agriculture contains contaminants and chemicals such as fertilizers, which promote overgrowth of algae, called blooms. Every summer, these blooms create a hypoxic area in the Gulf; August 2017 saw the largest, 22,000 square kilometers, about the size of New Jersey. As with the event at the East Bank, anything that can’t swim away from a hypoxic area dies.
Help is on the way, but the process is slow. In an effort to better protect the Flower Gardens, the National Oceanic and Atmospheric Administration proposed adding 15 additional areas covering approximately 383 square miles to the Flower Gardens. The Sanctuary Advisory Council formed a working group that reviewed public comments to a draft environmental impact statement published in June 2016, and recently presented its recommendations on specific boundary configurations. Bleaching and the East Bank event have lent an urgency to the lengthy expansion process.
“More than 99 percent of the Gulf is unprotected,” says oceanographer Sylvia Earle, a board member at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University–Corpus Christi. “Just like a healthy body is more resilient than one that is weak, a healthy reef where everything is protected is more resilient. Throughout the world, ocean systems are weakened and stressed, and the main threats are human pressures.”
Scientists studying the East Bank event suggest increased monitoring and sampling to help them understand it and better prepare for future threats. They recommend more frequent coral monitoring, additional permanent instruments to measure water conditions, and monitoring of the amount and quality of river water flowing into the Gulf.
Recent studies predict increased river flooding in North America during the next 15 years. Hurricane Harvey’s extreme rainfall in August 2017 led to higher levels of freshwater inflow into the Gulf, the effects of which have yet to be thoroughly evaluated. Another hot Texas summer could lead to more coral bleaching or other mortality events.
“The chances of a mortality event happening again are not small,” warns Steve DiMarco, oceanography professor at Texas A&M University.
Coral reefs like those in the sanctuary provide habitat, protection and food that support at least a quarter of all marine life. Many large, ocean-going animals gather around reefs to spawn or feed. These structures provide significant coastal protection around the world. Reefs also support commercial and recreational fishing and tourism industries, with the latter alone generating $36 billion globally every year.
In other words, what happens in the Gulf of Mexico and the Flower Gardens reverberates well beyond these waters. This Texas treasure is worth saving.
More in our reef series:Deep in the Gulf | Building More Reefs | Life at an Artificial Reef | Swimming with Sharks | Roar of the Lionfish
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