[Editor's note: The following post was written by Philine zu Ermgassen, a research fellow based in Cambridge, England. She works with the Conservancy’s Global Marine Team]
Oysters. Famous for being a delicious morsel, with a succulent, creamy texture. Less famous for being an ecological cornerstone in our estuaries.
But that’s exactly what they are. While sitting quietly on the ocean floor, a single oyster can vacuum up to 50 gallons of water a day through its little bivalve body. Which means those little guys can make a big difference.
When oysters filter water they remove particles, which they then either eat or deposit on the sediment. Either way, the water becomes clearer. And clearer water means more chance for seagrass and other vegetation to grow on the sea-bed, bringing a cascade of benefits for nature and for people.
Clear waters also mean better recreation for swimming, boating and fishing, and fewer toxic blooms and hypoxic events.
Great, right? It would be if we still had our wild oyster reefs left… which we almost don’t.
The catastrophic declines in oyster abundance across the U.S. are well documented. Less well known is the associated loss of benefits, such as clearer waters and more juvenile fish. Until now.
A study published this week sheds light on just how important water filtration by oysters used to be. And the results bring a clarity second only to, well, the oysters themselves.
Oysters today filter only a fraction of the water they used to. For example, 100 years ago oysters in Matagorda Bay filtered enough water to fill 320 Fenway Park stadiums every hour. Today this has dropped to just two.
At first glance this seems to be one more dire statistic, but the study also has two positive messages. First, well managed estuaries can still have thriving oyster fisheries and oyster populations today. This is evident in Florida’s Apalachicola Bay, where oysters are now more abundant there than historically. Second, this study provides a much-needed baseline to answer the important question “how much restoration is enough?”
That coastal restoration works and is needed there is no doubt. We know we want to improve on what we have. The issue is that in the marine world we have little or no idea of how things used to look. It is therefore difficult to determine any ultimate goal.
Restoration isn’t simply about rewinding the clock: restored habitats need to fit in alongside the many changing features of our coastline. In some cases it may no longer be feasible or desirable to restore oyster populations back to their pre-industrial abundance, before U.S. estuaries were developed as regions of industry and urban centers. After all, ships used to run aground on oyster reefs in the Chesapeake Bay and Charles River. The challenge is to assess what restoration should seek to achieve against this modern backdrop; that is exactly what Nature Conservancy scientists are trying to work out.
This study provides a framework for assessing estuaries, and for estimating how much restoration is necessary before oysters once more benefit our coastal waters on a large scale. Oysters alone are not going to clean our dirty estuaries, but in combination with better controls on pollution oyster restoration can make an important contribution – if we restore enough of them.
The good news here, is that oyster restoration works. Restoration successes are becoming commonplace from the West Coast, through the Gulf of Mexico to the North Atlantic. The success stories are remarkable, and the ambition and enthusiasm of those involved is seemingly boundless.
Even with modest increases of 15 adult and 15 young oysters per square meter, a single hectare of restoration can filter 20 Olympic swimming pools a day.
This work is a game changer. It illustrates that we can and are making a difference, and that while the need is great, if we play our cards right, and if we keep at the long road towards restoring our estuaries, we can succeed.
[Image: Chesapeake Bay oysters. Image source: Mark Godfrey/TNC]