Hurricane Harvey more than doubled the acidity of Texas' Galveston Bay, threatening oyster reefs
Published in Science & Technology News
Most people associate hurricanes with high winds, intense rain and rapid flooding on land. But these storms can also change the chemistry of coastal waters. Such shifts are less visible than damage on land, but they can have dire consequences for marine life and coastal ocean ecosystems.
We are oceanographers who study the effects of ocean acidification, including on organisms like oysters and corals. In a recent study, we examined how stormwater runoff from Hurricane Harvey in 2017 affected the water chemistry of Galveston Bay and the health of the bay’s oyster reefs. We wanted to understand how extreme rainfall and runoff from hurricanes influenced acidification of bay waters, and how long these changes could last.
Our findings were startling. Hurricane Harvey, which generated massive rainfall in the Houston metropolitan area, delivered a huge pulse of fresh water into Galveston Bay. As a result, the bay was two to four times more acidic than normal for at least three weeks after the storm.
This made bay water corrosive enough to damage oyster shells in the estuary. Because oyster growth and recovery rely on many factors, it is hard to tie specific changes to acidification. However, increased acidification certainly would have made it harder for oyster reefs damaged by Hurricane Harvey to recover. And while our study focused on Galveston Bay, we suspect that similar processes may be occurring in other coastal areas.
Scientists predict that climate change will make hurricanes stronger and increase the amount of rain they produce over the next several decades. Changes in ocean chemistry, caused by runoff from these storms, are becoming an increasing threat to many marine ecosystems, especially coastal reefs built by oysters and corals.
Coastal estuaries like Galveston Bay, where rivers meet the sea, are some of the most productive ecosystems in the world. Galveston Bay is the largest bay on the Texas coast and one of the largest in the U.S.; it covers about 600 square miles, roughly half the size of Rhode Island. Its extensive oyster reefs provide about 9% of the national oyster harvest.
Hurricane Harvey, the wettest tropical cyclone in U.S. history, made landfall on the Texas coast as a Category 4 hurricane on Aug. 26, 2017. Harvey stalled at the coast for four days, sitting over both land and ocean.
Maintaining contact with warm Gulf of Mexico waters fueled the storm with both energy and rainfall, allowing it to persist and drop extreme amounts of rain directly onto Houston and surrounding areas – up to 50 inches in four days. All of that rain and floodwater had to go somewhere, and much of it flowed into Galveston Bay.
The ocean acidification issues that we study are a well-known effect related to climate change. Human activities, mainly burning fossil fuel, emit carbon dioxide into the atmosphere. The ocean absorbs about one-third of these emissions, which alters ocean chemistry, making seawater more acidic.
Acidification can harm many forms of marine life. It is especially dangerous for animals that build their shells and skeletons out of calcium carbonate, such as oysters and corals. As seawater becomes more acidic, it makes these structures harder to build and easier to erode.