Why are the oyster reefs in trouble?

by Nancy Hadley

I have devoted 30+ years to oysters.  You might wonder how that is even possible.  What can you do with, for, or to oysters for 30 years?

My first endeavors were to figure out why oysters spit. Esoteric but intriguing. However, I couldn’t crack that nut which has puzzled better scientists than me. Later I was part of a team studying oyster reef ecology.  The oyster reef community is diverse, fascinating, and very hard to sample.  So the work goes on and on and on.

Oyster reefs are in trouble
Fish kill. Photo from the U.S. Geological Survey. Public domain image. https://pubs.usgs.gov/fs/fs12497/
Fish kill. Photo from the U.S. Geological Survey. Public domain image. https://pubs.usgs.gov/fs/fs12497/

At some point I became less interested in asking questions and more interested in taking some ACTION to help oyster reefs.  When you look at a South Carolina estuary or tidal creek, you might think there are oysters everywhere.  But the fact is that our oyster reefs are in trouble.

You probably immediately jumped to the conclusion that they are over-harvested, probably by unconscionable fishermen who just want to make a buck. That isn’t the answer though, or at least not the whole answer.  It’s a lot more complicated than that.

It’s infinitely sad, because oyster reefs should be self-sustaining.  After all thousands, perhaps millions, of new oysters move into the community every year.  We need oyster reefs in our ecosystem because they are a KEYSTONE SPECIES.  If we lose our oyster reefs, the entire ecosystem will change.

The consequences of fewer oysters

This has happened in the Chesapeake Bay, where oysters were all but wiped out due to overfishing and disease.  Without reefs, fish and other mobile fauna move on, looking for structure.  Without oyster reefs to filter the water, algae blooms out of control.  These algal blooms are toxic or simply use up all the oxygen, causing fish kills.

Without oyster reefs, food chains are disrupted.  Oyster waste is an important component of the food chain for bottom residents and bottom feeders. Without oyster reefs, boat wakes and wind-driven waves cause rapid erosion of fragile saltmarshes lining tidal creeks.

Coastal Development of Horlbeck Creek in Charleston Country
Image from NAIP Images. Public Domain.
Oysters are stuck, literally

So what is threatening our oyster reefs?  The short answer is too many people living on the coast.

Coastal development inevitably involves an increase in impervious surfaces (pavement, houses) and a decrease in vegetated land.  Rain runs off faster. It isn’t filtered. It’s full of pollutants and silt.

Silt is a big problem for oysters. Because they are stuck, literally.  Adult oysters are cemented in place. They cannot relocate if silt builds up around them.  They just smother.

Slow: No Wake Zone!

People move to the coast to be on the water.  This means they have boats.  In fact, South Carolina has the 4th highest number of boats per capita of US states.  And one of the biggest threats to oyster reefs is boat wakes.

Boat wakes are different than waves, and they are more destructive.  If you are operating a boat in tidal creeks, please watch your wake. Literally. Learn how your wake behaves, how it changes with your speed, and what it does to the shoreline. And now that you know, please adjust your boat handling to minimize the impact of your boat wake. It can be done.

Fewer oysters for us or more oyster reefs?
Marsh erosion due to boat wakes. Rockville, SC. Photo courtesy of Coastal Conservation League.
Marsh erosion due to boat wakes. Rockville, SC. Photo courtesy of Coastal Conservation League.

And then there is overharvesting.  Or more accurately, unsustainable harvesting.  The number of harvesters, and the number of oysters they harvest, really hasn’t changed. But if you have fewer oysters, and you take just as many, you are having a greater impact on the oyster reef.

We need to either harvest fewer oysters or build more oyster reef!  And that’s where the Department of Natural Resources comes in.

You can read the first part of this series, The Mystery of the Spitting Oysters.  Nancy Hadley is a marine biologist with the SC Department of Natural Resources where she heads up the Shellfish Management Program.