Artificial reefs are human-made structures that are either deliberately or unintentionally submerged underwater, commonly with the result of mimicking some characteristics of a natural reef. Artificial reefs alter local habitat by providing hard substrate and complex vertical relief where typically none previously existed (Bohnsack and Sutherland 1985, Sheehy and Vik 1992, Sheehy and Vik 2010). They may be created from a variety of sources and materials including the intentional sinking of ships and barges, rubble, concrete, rocks, stone, boulders, steel, and metal, etc. (Baine 2001). They may also be created through unintentional means (e.g., shipwrecks that can become historical in nature) and through structures built for other purposes (e.g., decommissioned oil and gas platforms, breakwaters1 , jetties, bridges, offshore lighthouses, air force towers, navigational aids, marine data buoys, etc.). These various materials have benefits and drawbacks when used in artificial reef construction (see Table 1 for examples).
The establishment of an artificial structure influences the surrounding underwater ecosystem by creating new habitat that can potentially change the abundance and distribution of living resources. Artificial structures can provide similar ecological functions as natural habitat, including developing epibiotic communities that create microhabitat for motile species, locally concentrate planktonic and pelagic food resources, alter current flows to provide sheltered areas, provide visual reference points, and create spawning sites (Bohnsack and Sutherland 1985, Sheehy and Vik 2010). Because of their ability to create habitat for a variety of marine life they are often popular destinations for divers, snorkelers, and fishermen. Therefore, their creation can also alter human use by shifting recreational diving and fishing patterns (Leeworthy et al. 2006, Leeworthy 2011).
General agreement exists in the scientific community that artificial reefs can effectively accumulate fish and other organisms (Bohnsack and Sutherland 1985). Somewhat less understood are the effects of artificial reefs on living resource production, their ability to act as stepping-stones that facilitate native and non-native species dispersal, how they affect disease frequency in fish and invertebrates, toxicological impacts, their long-term structural integrity, and changes to the socioeconomic conditions of adjacent coastal communities. The purpose of this paper is to summarize the scientific literature and findings on these subjects.