Secondary use material consists of natural material such as shells and rocks. According to the Guidelines for Marine Artificial Reef Materials, "over 80 percent of artificial reefs in the United States have been created using secondary use materials." One rock, however, doesn't make a reef. Suitable locations for artificial reefs are rock-lined shelves less than 80 feet under water. That's a lot of rock or shell to find, remove and transport. Rock, however, has no manmade substances, which lessens the impact on the fish living in the area before reef creation.
Sometimes companies produce formed concrete that simulates the base structure of reefs. It provides suitable habitat for fish and crustaceans that resembles reel reef bases as it erodes over time. The need for environmentally safe artificial reef spawned the creation of a special concrete mix consisting of cement, sand and other materials for a long life span. This style of artificial reef exists in Sarasota Bay, Florida.
Some states and groups resorted to dropping manmade structures into the ocean as a cost effective way to get an artificial reef. Old subway cars, automobiles, and old ships are dropped into the ocean to change the barren sea floor into a fisherman's favorite spot. Artificial reefs made of subway cars exist off the coast of Delaware, Maryland, Virginia and New Jersey. Using manmade structures that are past their usefulness has one problem. Many of the old items contain harmful chemicals such as asbestos embedded in the walls or even the glue which held the item together. Finding the right item in large enough quantities to form a reef takes patience and a firm eye for details. It may delay the process.
