A man-made marine habitat constructed for the purpose of encouraging the growth of sea life. Some artificial reefs can also be used to control coastal erosion. Generally, the artificial reef provides a surface for invertebrates to go–including algae, corals, barnacles and oysters, whose presence promotes life for other types of fish. Artificial reefs come in many forms. Sinking oil rigs, deploying rubble and constructing concrete or PVC structures underwater are some examples. Old or modern shipwrecks turn out to serve as artificial reefs when preserved on the sea bed.