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Oysters and Ecology: An Overview

Liz Clift

Recently, I wrote about the tradition of oyster stuffing—and the reality that some people eat oysters at all (not to yuck your yum, as the youth I used to work with would say, but it bears repeating: ew!).

In this blog, which is part of a series on bivalves, I’m going to focus more on the ecology of oysters. We’ll start again in New York. In the last blog, you’ll remember me saying that oyster production in New York peaked between 1880 and 1910, which was part of the “progressive era” in American history—a time categorized by historians as a period of modernization of natural resource management (among other things). However, this wouldn’t help oysters.

As oyster populations decreased, the bivalves were no longer able to filter all the water in New York Harbor (an adult oyster can filter about 40-50 gallons of water a day), and toxicity became a concern. By 1927, the last oyster bed in New York was closed due to health concerns, and there weren’t any improvements in the health of oyster beds until the 1972 Clean Water Act (CWA). Nearly 45 years later, however, the oysters of New York Harbor are still too polluted to eat and dredging can further complicate oyster health by stirring up centuries worth of pollution that has settled onto the harbor floor.

Overharvesting and high levels of pollutants aren’t the only threat to oysters. Warmer ocean temperatures are leading to ocean acidification—higher levels of carbon dioxide (CO2) are present in the water—which can prevent the shells of young oysters from solidifying. In the previous blog, I talked about pathogens which also impact oysters—including Vibrio, MSX, and dermo—so I won’t rehash that here, but warmer waters can mean that these diseases are spreading beyond their historical presence. In addition, oysters still have to deal with their natural predators, which in addition to people include:

  • Fish (especially for young oysters);
  • Birds;
  • Blue crabs;
  • Sea otters;
  • Sea stars (which use pressure* to force open the oyster’s shell); and
  • Snails, such as the Atlantic oyster drill.

The plight of oyster is so bad that portions of the East Coast only have 1% of their historic natural oyster population—despite efforts to repopulate oysters. Fortunately, New York and many other areas are taking oyster repopulation serious. This is good because oyster reef abundance has decreased approximately 85% globally in the past century. Oysters help filter pollutants from water (though they can do nothing about heavy metals and PCBs, except absorb them into their bodies, which can render them dangerous to humans). Oyster reefs can also help stabilize sediments and slow wave-induced erosion, which can make a big difference in areas where coastal loss is a problem.

Although restoration efforts are underway up and down the East Coast and in other parts of the world, it will likely be years before oyster populations are restored enough to provide the same level of various ecosystem services that they once provided—and that’s assuming oyster harvesting is well-managed, and that diseases that can affect oysters don’t boom alongside these restoration efforts.

These restoration efforts, like all restoration efforts, should also include monitoring. This can help evaluate the state of the habitat, detect recruitment and survival rates, understand how the ecosystem is functioning, and recognize the interaction of species in and near the reefs.

*This video shows mussels, not oysters, but you get the idea.

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