Artificial reefs

An artificial reef (AR) is a human-created freshwater or marine benthic structure. Typically built in areas with a generally featureless bottom to promote marine life, it may be intended to control erosion, protect coastal areas, block ship passage, block the use of trawling nets, support reef restoration, improve aquaculture, or enhance scuba diving and surfing. Early artificial reefs were built by the Persians and the Romans.

An opportunity artificial reef is built from objects that were intended for other purposes, such as sinking oil rigs (through the Rigs-to-Reefs program), scuttling ships, or by deploying rubble or construction debris. Shipwrecks may become artificial reefs when preserved on the seafloor. A conventional artificial reef uses materials such as concrete, which can be molded into specialized forms (e.g. reef balls). Green artificial reefs incorporate renewable and organic materials such as vegetable fibres and seashells to improve sustainability and reduce energy consumption, pollution, and greenhouse gas emissions. In some cases, artificial reefs have been developed as artworks.

Artificial reefs generally provide hard surfaces where algae and invertebrates such as barnacles, corals, and oysters attach and spaces where different sizes of fishes can hide. The accumulation of attached marine life in turn provides intricate structures and food for assemblages of fish. The ecological impact of an artificial reef depends on multiple factors including where it is situated, how it is constructed, and the ages and types of species involved. While the artificial reefs allow for coral growth, it changes the ecosystem as the relative growth for different species is not always the same. Studies have found that macroalgal, cyanobacterial groups, and coral that are fast growing, grow in artificial reefs at different rates than they would grow in natural reefs.

Considerable research is being done into construction methods and the effects of artificial reefs. Many of the materials used early on are now considered undesirable. A 2001 literature review suggested that about half of the reefs studied met their objectives. Long-term planning and ongoing management were identified as essential factors in success. A more recent analysis of reefs world wide between 1990 and 2020 concludes that artificial reefs can be useful tools for restoring marine ecosystems if they are strategically designed to suit their specific location and its resource needs.