The concept of keystone species was recognized 50 years ago by Robert Paine, a zoologist who was looking to disrupt the way that science understood nature. Prior to Paine’s pioneering work, scientists looked up the food chain, identifying the impact of disruptions in the lower levels (e.g., plants and small predators) on animals in the higher levels.
Paine turned this thinking on its head (for those of you interested, Kuhn’s work on scientific revolutions explained how these paradigm shifts are a primary mechanism for scientific advancement).
Paine investigated the impact of the apex predator on the environment. The apex predator resides at the top of the food chain, for example, lions, tigers, sharks and, frankly, us. Of course, it is not environmentally conscientious to remove an apex predator from the environment and certainly not possible on a large scale. But Paine found that small tidal pools were ideally suited to this test. He relocated starfish (which are the apex predator of tidal pools) from one tidal pool and left a neighboring tidal pool intact.
To his surprise, removing starfish drastically impacted the biodiversity of the tidal pool. Other tidal pool creatures such as periwinkles, whelks, barnacles, crabs, and sea urchins virtually disappeared as mussels usurped the tidal pool.
The good news, he reintroduced starfish into the tidal pool and eventually the genetic diversity of the tidal pool returned.
This gave birth to the notion of “keystone species.” Keystone species are so crucial to the environment that to eliminate them effectively dismantles its diversity. Starfish are a keystone species in tidal pools.
Since his discovery, scientists began identifying other keystone species. At first, they focused on apex predators such as wolves in the US, panthers in South America, and largemouth bass in streams.
Later they were able to identify keystone species that were not apex predators; for example, Wildebeests in the Serengeti.
Why is this exciting? Well, it means that science has given us a formula for repairing the environment…bring back its keystone species and let nature do its work.
It isn’t a slam dunk, many scientists believe that the concept of keystone species is too simplistic. They believe that nature is too complicated to allow just one species to “make or break” it. But even if that is true (and it probably is); at least the concept of keystone species gives us a place to start.
What does that mean for the Eastern Shore?
Many scientists believe that oysters are a keystone species. And this keystone species is in trouble; wild oysters are down to 1% of their precolonial levels.
If we can reintroduce the oyster population to its earlier levels, our estuaries on the Eastern Shore (for those who don’t know most of our rivers and the Chesapeake Bay are estuaries) will recover.
A single oyster filters fifty gallons of water a day. Other filter feeders such as mussels, clams, sea grapes, parchment worms and even the annoying barnacle live in oyster reefs. The oyster is not only the most effective, but it builds the habitat for the other filter feeders.
Advocacy groups recognize the importance of the oysters and have worked tirelessly to pass legislation, secure funding, monitor our estuaries, educate the public and research our vast Chesapeake Bay estuaries. Their work has led to beneficial legislation, increased funding, an educated population and thousands of acres made available for oyster farming. Without their efforts, I cannot imagine what our estuaries would be now.
The Chesapeake Bay Foundation effectively advocated for a multi-state event to improve the estuaries by creating the Chesapeake Clean Water Blueprint. All states that are part of the Chesapeake Bay watershed have committed to reducing the pollution going into our estuaries.
But without addressing the keystone species it seems like we are effectively rearranging the deck chairs on the Titanic.
Only four Eastern Shore estuaries have been targeted for full scale introduction of oysters: Harris Creek, Little Choptank, Tred Avon and Manokin Rivers.
The results from the 2015 Harris Creek reintroduction are no less than stunning, suggesting that oysters are a keystone species in the Chesapeake Bay region. Over 2 billion oysters were planted in 350 acres. During summer months the entire volume of Harris Creek can be filtered in ten days. Scientists estimate that the oyster reefs in Harris Creek will remove one million pounds of nitrogen from the Chesapeake Bay in a decade. Other filter feeders are getting into the act and mussels and sea squirts living on the reef filter more than 40% of the total load.
First let me emphasize that I am not an expert. It would be extreme hubris for me to claim that I have the answer. Hundreds have dedicated their careers and their lives to studying this problem, they are the experts. I have no doubt that I have oversimplified the issues and the efforts.
But my mind keeps coming back to logic that if oysters are a keystone species, we can’t restore our estuaries without them. It would be akin to Dr. Paine removing the mussels from the tidal pools that don’t have starfish, it might help temporarily, but the permanent solution only occurred when he reintroduced the keystone species.
Reintroducing oysters is fraught with political and financial minefields. Lower salinity levels from higher than average rainfalls have negatively impacted mid shore oysters. Viruses, overharvesting, runoff, and chemicals make it even more challenging. Many reefs have been dredged out of existence and oysters suffocate in the silt.
Very hard choices are required to restore our keystone species.
Solutions to restoring oysters are controversial. (For example, our popular governor vetoed a bill to permanently protect five oyster sanctuaries, fortunately his veto was overridden by the General Assembly.)
Oyster farming is a solution, it addresses the public’s love of oysters and cleans the estuaries. Through their tireless efforts, advocacy groups were able to get Maryland to make available 600,000 acres for oyster farming. However, oyster farming is under attack by residents complaining that the oyster farms are ugly and mar their views.
Two politically untenable solutions involve the harvesting of wild oysters: eliminating oyster dredging and imposing a temporary moratorium.
The only thing that everyone agrees upon is that we cannot restore the oysters on the backs of the watermen. During the moratorium, we need to provide revenue opportunities for watermen, such as building oyster reefs for the next generation.
We could enlist aid from waterfront owners by making it easy (or possible) for them to install artificial (e.g., spat implanted rebar) oyster reefs along their shorelines. One resident trying to pursue this option has been unable to find the right organization to help.
We need to continue to develop species that are immune to viruses that can flourish at lower salinity levels.
In the short term, restoring oyster reefs would involve a lot of work, expense and cause heartache for many.
But science has given us a blueprint to restore the Chesapeake Bay and its estuaries; do we have the courage to use it?
Angela Rieck, a Caroline County native, received her PhD in Mathematical Psychology from the University of Maryland and worked as a scientist at Bell Labs, and other high-tech companies in New Jersey before retiring as a corporate executive. Angela and her dogs divide their time between St Michaels and Key West Florida. Her daughter lives and works in New York City.
Letters to Editor
Bob Moores says
This is a great article, well written and informative for me. I was familiar with the relevance of a keystone species, but did not know that oysters were one, or the role they play in the Bay/estuary ecosystem. Thank you, Dr Rieck.