Eastern Oysters on the Boston Harbor Islands: Filter Feeders Under Pressure

Eastern oysters. NOAA Fisheries.

An imagined interview

The Boston Harbor Islands series "Island Interviews" imagines conversations with the islands' non-human residents to show how people and ecosystems interact. In this one, a park ranger picks a careful path across a tidal flat on Spectacle Island to "talk" with an eastern oyster (Crassostrea virginica) — a mollusk well known on dinner plates, but whose life is far less familiar.

Life between the tides

Oysters live in the intertidal zone, underwater at high tide and exposed at low tide. They close up when the tide goes out — a break from eating. (Watch your step: they don't like being trodden on.)

Filter feeding

An oyster is a filter feeder: it draws water in over its gills, keeps the bits of food and pushes the water back out. In doing so it also removes nutrients such as nitrogen, which matters because:

• too much nitrogen can set off algae blooms;
• when the blooms die, they can use up much, or all, of the water's oxygen.

By filtering, oysters help prevent that loss and keep water clean for other species. On a good day, one oyster can filter almost 50 gallons, storing some of the nitrogen in its shell.

Shells and acid

Oysters can swim — but only as tiny larvae. Then they build a shell of calcium carbonate, the same substance used in stomach medicine to neutralize acid. That makes ocean acidification a real threat: seawater is much more acidic than before the Industrial Revolution, and climate change looks set to push it further.

How to help

• Cut carbon emissions.
• Get to know oysters: join a participatory science project such as Bivalve Quest and help scientists learn how to protect them and other marine species — while the oysters keep the water clean in return.

Sources

Based on "Island Interviews: Eastern Oyster," Boston Harbor Islands National Recreation Area, National Park Service; a work of the United States government in the public domain.