Spat: How a Drifting Oyster Larva Becomes a Reef

An oyster starts life as a drifter. The tiny larvae swim freely through the water until they find a suitable place with a structure to settle on. The moment a larva attaches itself permanently to a surface, it has a new name: spat. And spat, generation after generation, is how oyster reefs are built.

An oyster bed, with spat shown in the inset. As generations of spat grow into adult oysters, they form dense clusters called oyster reefs or beds. Credit: NOAA.

Where oysters live

Oysters are a kind of shellfish found in brackish and salt water bays, estuaries and tidal creeks.

Farming oysters

Oysters are often cultivated, for food and for pearls. Oyster and shellfish farming depends on getting larvae to settle successfully onto a chosen surface — usually other oyster shells or ceramic tiles — in a hatchery or in the wild. The tiles or shells carrying spat are fixed to frames or placed in cages and sunk along an intertidal area, or hung from a long line. From then on, the oysters look after themselves, filtering all the nutrients they need from the surrounding water.

Why oyster reefs matter

• Cleaner water. Oysters are filter feeders, so they help keep the water clean. That helps underwater grasses such as wild celery grow, and those grasses are important habitat for other species.
• Shelter. Oyster beds form large, complex structures where fish, crabs and other aquatic animals hunt for food and hide from predators.

Sources

Based on "What is spat?" from NOAA's National Ocean Service, a work of the United States government in the public domain.