An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets, or improve surfing.
Many reefs are built using objects that were built for other purposes, for example by sinking oil rigs (through the Rigs-to-Reefs program), scuttling ships, or by deploying rubble or construction debris. Other artificial reefs are purpose built (e.g. the reef balls) from PVC or concrete. Shipwrecks may become artificial reefs when preserved on the sea floor. Regardless of construction method, artificial reefs generally provide hard surfaces where algae and invertebrates such as barnacles, corals, and oysters attach; the accumulation of attached marine life in turn provides intricate structure and food for assemblages of fish.
The construction of artificial reefs began in ancient times. Persians blocked the mouth of the Tigris River to thwart Arabian pirates by building an artificial reef and during the First Punic War the Romans built a reef across the mouth of the Carthaginian harbor in Sicily to trap enemy ships within and assist in driving the Carthaginians from the island.
Artificial reefs to increase fish yields or for algaculture began no later than 17th-century Japan, when rubble and rocks were used to grow kelp. The earliest recorded artificial reef in the United States is from the 1830s, when logs from huts were used off the coast of South Carolina to improve fishing.
Beginning before the 1840s, US fishermen used interlaced logs to build artificial reefs. More recently, refuse such as old refrigerators, shopping carts, ditched cars and out-of-service vending machines replaced the logs in ad hoc reefs. Officially sanctioned projects have incorporated decommissioned ships, subway cars, battle tanks, armored personnel carriers, oil drilling rigs and beehive-like reef balls.
A newly constructed electric reef set up by Gili Eco Trust in Indonesia.
Human-created objects provide hiding places for marine life, like this Sarcastic fringehead
Artificial reefs tend to develop in more or less predictable stages. First, where an ocean current encounters a vertical structure, it can create a plankton-rich up-welling that provides a reliable feeding spot for small fish such as sardines and minnows, which draw in pelagic predators such as tuna and sharks.
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Next come creatures seeking protection from the ocean’s lethal openness—hole and crevice dwellers such as grouper, snapper, squirrelfish, eels and triggerfish. Opportunistic predators such as jack and barracuda also appear. Over months and years the reef structure becomes encrusted with algae, tunicates, hard and soft corals and sponges.
3D printing technology has been employed both to create molds for cast ceramic and concrete artificial reefs, and to directly create artificial reefs, also through the use of environmentally friendly materials.
An electric reef is an artificial reef where an small low voltage electric charge is applied to a sub-sea metallic structures that causes limestone to precipitate onto a metal frame onto which coral planulae can then attach and grow; the process also speeds up post-attachment growth.
Artificial reefs can show quick increases in local fish population rehabilitation, coral reef and algae growth. However, far more than half the amount of biomass found on artificial reefs is attracted from other areas rather than developing there. James Bohnsack, a biologist with the National Marine Fisheries Service (NMFS) concluded artificial reefs do not increase fish populations. Instead they operate as fish aggregating devices (FADs) bringing in fish from other reefs. Concentrating fish on a reef also makes for easier fishing. Research continues.
The fish attracted to artificial reef zones vary from reef to reef depending on its age, size and structure. Large reef structures such as large sunken ships attract larger fish.
The use of shipwrecks in rocky zones creates a new tropic structure for the local ecosystem. They become the home for certain species and many nearby animals migrate to the shipwreck. This unbalances the natural ecosystem and alters many other habitats.
Florida has one of the most active artificial reef programs among the 15 Gulf and Atlantic coastal states involved in artificial reef development. Since the 1940s, more than 3,750 planned public artificial reefs have been placed in state and federal waters off Florida’s coast. The FWC Artificial Reef Program provides financial and technical assistance to coastal local governments, nonprofit corporations and state universities to construct, monitor and assess artificial reefs.