Currents may carry them upward into water that is too fresh, or outward into the salty Gulf where they will perish. Many organisms feed upon the larvae or produce substances which poison them. Pollution from industrial waste may cause larval death. However, that small percentage can result in tremendous numbers of tiny oysters. Spat will set upon many different materials, such as bricks, bottles, cans, tires, even crabs and turtles.
Oyster spat are gregarious, that is, they tend to settle where some spat are already present.
When spat are plentiful, overcrowding may occur but this tendency helps to maintain the oyster population on established reefs and is a means by which new reefs may evolve. Upon setting, the tiny spat begins to secrete new shell in successive layers, expanding in all dimensions. Special cells in the mantle covering secrete most of the shell material, although it can also be deposited by mantle cells within the valves. The oyster can, in effect, patch up its old home while building an addition to it. Sometimes, sand grains, shell fragments or other particles become lodged within the mantle tissue.