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This extreme acidification lasted for more than three weeks. Bay waters became corrosive not only to more sensitive larval and juvenile oyster shells, but to adult oyster shells as well. Scientists had predicted that increasing CO₂ could cause this scale of coastal acidification but did not expect to see it until around the year 2100.
The fresh water from Harvey also caused a severe oyster die-off in the bay because oysters need slightly salty water to survive. Harvey struck in the middle of oyster spawning season, and acidification may have slowed reef recovery by making it harder for young oysters to form new shells. Officials at the Texas Parks and Wildlife Department have told us that four years later, in late 2021, some Galveston Bay oyster reefs still showed very low additions of new oysters.
Other coastal areas at risk
Only a few studies, including ours, have analyzed how tropical cyclones affect coastal acidification. In our view, however, it is highly possible that other storms have caused the kind of extreme acidification that we detected in the wake of Harvey.
We reviewed the 10 wettest tropical cyclones in the U.S. since 1900 and found that nine, including Harvey, caused large amounts of rain and flooding in coastal areas with bay or estuary ecosystems. Other storms didn’t produce as much rainfall as Harvey, but some of the affected bays were much smaller than Galveston Bay, so less rain would have been needed to replace seawater in the bay and cause a similar level of acidification to what Harvey produced.
We think that this likely has already occurred in other places struck by hurricanes but went unrecorded because scientists weren’t able to measure acidification before and after the storms. As climate change continues to make tropical cyclones larger and wetter, we see storm-induced acidification as a significant threat to coastal ecosystems.
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