Oysters are carnivorous invertebrates that can live up to 20 years in captivity. Although there are many varieties of edible oysters, there are only five actual species of oyster: Pacific Oysters, Kumamoto Oysters, Atlantic Oysters, Olympia Oysters and European Flat Oysters.
Oysters have extremely powerful adductor muscles that allow them to close their hard shells tightly when threatened. They feed by filtering water through their gills to extract algae and other microscopic creatures, filtering from 30 to 50 gallons of water a day in the process. By filtering the water in this way, oysters also clean the water, removing polluting toxins and particles. For this reason, they can also retain toxins in their flesh, which makes them sensitive to coastal pollution in their habitats and potentially dangerous for human consumption when harvested from polluted areas.
Prior to European settlement, the island of Manhattan was surrounded by vast beds of oysters. When the Dutch arrived in the 18th century, the prevalence of oysters made them a popular food item for the settlers. In fact, New York Harbor was home to such an immense oyster population that it became the primary source of oysters worldwide. Oysters are a rich source of zinc.