For Oysters, Climate Change Means More Flooding and A Harsh Environment

“And this,” my uncle told me, “is the best food to ever exist.” He spun the icy plate around, with its small dishes of cocktail sauce and horseradish, it’s wedges of lemon, and presented me half of a glistening shell containing a small lump of briny meat. “It’s local,” he informed me.

An oyster. Raw. As a kid who grew up in the Midwest, tipping my head back for the first time to let that gray lump, the salty brine, and a few chips of dislodged shell past my teeth felt… exhilaratingly alien. That little creature, all in a few seconds, gave me a window in to my new home. The culture; the history; the cuisine; the economy; the ecology were all soaked into that little bivalve. All of the region’s inhabitants, from the earliest humans to the modern denizens, have enjoyed this unique pleasure. And now, so had I.

The Chesapeake Bay’s oysters play an important role in Maryland; both on our plates and for the health of the bay. They’re cherished, but they also face adversity. “Oysters are very sensitive and responsive to environmental changes,” Matthew Gray tells me; his voice crackling through the speaker on my desk phone. Gray studies how changes in the environment impact the bay’s oysters at the University of Maryland’s Center for Environmental Studies.

For Gray and other ecologists, human-caused impacts like climate change and agricultural pollution are cause for concern. One such consequence of a warming climate is increasingly powerful storms that dump higher volumes of rain faster than before; warmer air can hold more water. As these torrents fall, rain water can enter salty rivers so fast that they can actually start to run fresh. That can stress oysters.

“Feeding rates are salinity dependent,” Gray tells me. “Outside of their optimum, feeding rates decline and will generally cease at very low levels.” If that happens, entire areas can experience oyster die-offs. “They may still expend energy to respire, but they aren’t taking in any more food and are likely headed towards a moribund state.” After about a week of extreme salinity stress, they may die.

These events are a threat to oysters that likely won’t lessen anytime soon; as much because of changes up on land as ones in the atmosphere. As rain from these intensified, short duration storms increase, it’s falling on an increasing amount of cement, asphalt, and compacted earth from urban development. With the sprawl of our communities, we have unintentionally removed the typical roadblocks that would slow fresh rain water as it runs into salty rivers, bays, and oceans.

Beyond negatively impacting oysters, this bum rush of unimpeded rain water can have disastrous impacts on humans directly. In May of 2018, heavy rains in Ellicott City, Maryland turned roads into surging rivers and left potentially hundreds of millions of dollars of damage. The grand total is still being tallied. It was declared a once-in-a-thousand-year flood.

Except for one thing. The same situation had played out almost identically two years before. Then, as now, many observers pointed to a lack of proper flood planning, an over-abundance of impermeable surfaces, and the effects of climate change.

This kind of climate-change-super-charged, impermeable-surface-driven, oyster-killing event was also seen recently in Texas. The oysters of Galveston Bay experienced an extended period of effectively zero salinity in 2017 after record breaking rains from hurricane Harvey surged into their habitat. The total effect is still being assessed, but there is fear of low oyster harvests for the next few years. A similar situation lead to an oyster die-off in the spring of 2011 when heavy rains killed upwards of 80% of oysters in the northern Chesapeake Bay.

These storms also present dangers for marine animals beyond just a lack of salt water. Powerful storms can also pull more pollutants from human activities on land into the oyster’s environment. As nitrogen and phosphorous from agricultural fertilizers and other sources are washed off human-altered surfaces and into the watershed, they can cause a spike in algae growth; otherwise known as a “bloom.” While these blooms are active, they can blot out sunlight from reaching other aquatic plants like the Chesapeake Bay’s all-important sea grass. But once the algae die, they are broken down by bacteria which consume a large portion of available oxygen and spit out carbon dioxide as they feast. The result is a dead zone which can affect surrounding ocean life in two ways.

First, the lack of oxygen in the water makes it difficult or impossible for many animals to exist there. Fish, for instance, will either evacuate or effectively suffocate when a dead zone forms. The oyster, unfortunately, can’t leave these dead zones.

The second effect is the spike in carbon dioxide which forms carbonic acid and creates more acidic water. This rising acidity can stress oysters and damage their calcium carbonate-based shells. For context, the corrosion of calcium-based structures by carbonic acid is why your dentist tells you to avoid soda; the high amount of dissolved CO₂ in soft drinks is what makes them so acidic and damaging to teeth.

Ocean acidification is also driven by higher levels of carbon dioxide in the air; an effect of climate change more broadly. As the oceans absorb more and more CO₂ from the atmosphere, it creates more acidic conditions everywhere. Warmer water, yet another climate symptom, can also stress oysters; especially in shallow waters.

When you combine all of these factors, it creates a future that is increasingly harsh on one of Maryland’s most iconic harvests. Not to mention putting the health of those who enjoy them at risk. There is also the recent finding that broken-down pieces of plastic are finding their way on to our plates through mussels and oysters, but that’s a story for another day.

With the pressures of climate change and other human impacts, it’s unclear what kind of future the Chesapeake Bay oyster will find itself in. Whether through desalination, rising water temperatures, polluted run-off, dead zones, over-harvest, urbanization, or acidification; human activity is having a negative impact on a food held so dear by so many.

For those people, the oyster is a symbol. Of history and culture. Of belonging and freedom. Of the sea. It’s a food that connects people to their community and their ecosystem. Tragically, our actions are damaging these connections. But we know what we can do to preserve this curious, shelled creature. As usual, it’s a battle with ourselves to make meaningful changes.

I can still conjure up the emotion of that first oyster, with its tangy finish, as it slid past my tongue. Hopefully, far into the future, that memory won’t give away my age.

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