An artificial reef is a structure made by people to help underwater life grow. These reefs are often placed in areas with flat, featureless ocean floors to support marine life. They can be built to stop erosion, protect coasts, block ships, stop fishing with large nets, help repair natural reefs, improve fish farming, or make scuba diving and surfing better. The first artificial reefs were made by the Persians and Romans.

An opportunity reef is created using items that were not originally meant for this purpose, such as old oil rigs (through a program called Rigs-to-Reefs), sunken ships, or construction waste. Shipwrecks can also become artificial reefs if they stay on the ocean floor. A conventional artificial reef uses materials like concrete, which can be shaped into special forms, such as reef balls. Green artificial reefs use natural materials like plant fibers and seashells to help the environment by reducing pollution and energy use. In some cases, artificial reefs are designed as art.

Artificial reefs give hard surfaces for algae and sea creatures like barnacles, corals, and oysters to attach to. They also provide hiding spots for fish of different sizes. As marine life grows on the reef, it creates structures and food for groups of fish. The effect of an artificial reef on the environment depends on where it is placed, how it is built, and the types and ages of species living there. While artificial reefs can help corals grow, they may change the ecosystem because different species grow at different rates. Studies show that fast-growing plants, algae, and corals grow differently on artificial reefs compared to natural ones.

Scientists are studying how to build artificial reefs and their effects on the environment. Many older materials used for reefs are no longer considered good choices. A review from 2001 found that about half of the reefs studied met their goals. Long-term planning and regular care are important for success. A recent study from 1990 to 2020 found that artificial reefs can help restore ocean ecosystems if they are carefully designed to fit the needs of their specific location.

History

Artificial reefs have been created for many years. Historian Diodorus Siculus wrote that during the First Punic War around 250 BC, the Romans built an artificial reef to block the harbor of Lilybaeum. They used stones, construction materials, and large timbers with anchors placed in the channels. Similarly, the Persians built an artificial reef to stop Arabian pirates by blocking the mouth of the Tigris River.

Artificial reefs designed to grow fish or algae were used as early as the 17th century in Japan. People placed rubble and rocks in the water to help kelp grow. The first recorded artificial reef in the United States was in the 1830s, when logs from old huts were placed near South Carolina’s coast to improve fishing. In the Philippines, a traditional fishing method called "fish nests" (also known as gango, amatong, or balirong) uses rocks and waterlogged wood to build mounds in shallow tidal areas. These mounds attract fish and crustaceans. During low tide, people surround the mounds with nets and dismantle them piece by piece to harvest fish. After each harvest, the mounds are rebuilt. This method has been used to catch young groupers, which are later used to start aquaculture projects. Fish nests were widely used before 1939.

Before the 1840s, American fishermen used interwoven logs to create artificial reefs. In recent years, items like old refrigerators, shopping carts, abandoned cars, and unused vending machines have been placed in unofficial reefs. Official reef projects have included decommissioned ships, subway cars, battle tanks, armored vehicles, oil rigs, and structures shaped like beehives called reef balls.

Purposes

Artificial reef structures (ARs) serve many purposes, such as protecting, improving, and restoring marine ecosystems. They also help support human activities like fishing, diving, and surfing. Artificial reefs can be used to fix environmental damage, restore habitats like kelp forests and coral reefs, and increase the variety of marine life. In fisheries management, they may help increase the number of fish that are important for recreation and business, improve fishing results, and protect fish populations. They can also shield underwater habitats from harmful fishing practices, stop coastal erosion, and support eco-tourism by encouraging activities like diving and surfing.

The way artificial reefs are designed and built depends on where they are placed and what they are meant to do. A reef made for one purpose might not work well for others. Early artificial reef projects often failed or had limited success. Recent studies from 1990–2020 show that artificial reefs, when carefully planned to match the ecosystem they are placed in, can help restore marine environments. Experts suggest comparing artificial reefs to natural ones before and after construction, monitoring reefs over time, and focusing on the shape and structure of the reef material.

On artificial reefs meant to improve ecosystems, marine life tends to develop in predictable stages. First, ocean currents can create areas rich in plankton near vertical structures, attracting small fish like sardines and minnows, which in turn draw larger fish like tuna and sharks. Later, fish that need shelter, such as grouper and eels, move in. Over time, the reef becomes covered with algae, corals, and sponges.

An electrified reef uses a small electric charge on a metal frame underwater to help limestone form, allowing coral to attach and grow faster.

3D printing has been used to create molds for artificial reefs and to make reefs directly from materials like ceramic and concrete. Scientists are also developing eco-friendly materials, such as Archireef’s 3D-printed terracotta tiles. These tiles are safe for marine life, break down naturally, and match the pH level of coral. A project in Hong Kong found that 95% of corals survived on these tiles after three years, which is much better than older methods.

Restoration efforts on artificial reefs include moving corals, releasing coral larvae, and growing corals in nurseries. For example, the Coral Restoration Foundation in Florida grows important coral species and replants them on damaged reefs. A 2023 review says artificial reefs can help restore marine ecosystems if they are designed properly for each location.

There is interest in using artificial reefs to store carbon and fight climate change. Coastal plants, algae, and phytoplankton are known to absorb carbon from the air. Scientists hope artificial reefs can add to this by increasing marine life that stores carbon.

RGV Reef, a large artificial reef in the Gulf of Mexico, is being studied for its ability to capture carbon. Another area near Juehua Island in China is also being tested. Scientists say factors like water movement, marine life, and technology must be considered when measuring carbon storage. Near Juehua Island, M-shaped reefs helped improve water conditions for carbon storage, but local marine life was limited. Experts suggest introducing the right species to improve results.

In the Caribbean, researchers found that placing artificial reefs near seagrass meadows can create a cycle where reefs attract fish, and the fish help seagrass grow. This improves seagrass productivity and provides food and shelter for marine life. Studies suggest seagrass beds in the Caribbean could store large amounts of carbon.

Some artificial reefs are built to stop coastal erosion. Their shape and how they affect water movement are important for reducing erosion. Some reefs are designed to absorb wave energy before it hits the shore, while others trap sand to build up beaches. Reefs are often custom-made for each area and may support specific types of marine life.

Some artificial reefs, like those for surfing, are not focused on improving ecosystems. An early surfing reef called Hoppy’s Reef near California failed in 1971. Later projects include Cable Station Reef in Australia (1999), Narrowneck Reef in Australia (2000), Chevron Reef in California (2000, removed 2008), and Boscombe Surf Reef in England (2009, closed 2011).

Artificial surfing reefs are made from materials like concrete, rocks, and sand-filled bags. These materials last different amounts of time, with some degrading faster than expected. Some experts say sand-filled bags are not reliable. Using rocks has raised safety concerns for surfers, but others think rocks are better for structural strength.

Besides improving surfing, artificial reefs may also help protect coasts, support research, and sometimes improve habitats. However, different materials are used for surfing reefs compared to reefs meant to help ecosystems.

A 2012 study found that artificial surfing reefs often did not meet their goals, such as improving surfing conditions. For example, Chevron Reef (Pratte’s Reef) did not achieve its intended purpose.

Environmental concerns

Environmental concerns about artificial reefs include the risk of damaging natural areas during installation. These reefs might change how marine life lives by bringing in non-native species or drawing fish, eggs, and larvae from nearby natural habitats. They could also gather fish in one place, making it easier to catch them and leading to overfishing and harm to fish populations over time. Materials used in artificial reefs might break down or release harmful substances like paint, oil, and plastics, which can hurt natural habitats. Broken parts of the reefs might become ocean waste or wash up on natural reefs and beaches.

Many marine animals move frequently. The types of fish found near artificial reefs depend on the reef's age, size, and structure. Different species and life stages of the same species prefer different habitats. For example, young Red Snapper (Lutjanus campechanus) are more likely to live on vertical artificial reef structures, but older Red Snapper return to muddy or sandy areas as adults. Understanding how marine organisms interact with their environment is important for managing marine resources and studying how artificial reefs affect ecosystems. When placing artificial reefs, planners should consider existing natural habitats and the needs of species at all life stages, including areas where they reproduce or grow.

Using shipwrecks or oil rigs as artificial reefs creates a new structure for local ecosystems. Artificial and natural reefs often have different types of life. Unless artificial reefs are built to look like natural ones, they may not support the same variety of life over time. For example, the Sint Eustatius reef, which is about 200 years old, has a healthy ecosystem but has fewer and different coral species than a nearby natural reef.

Artificial reefs can sometimes harm natural ecosystems by bringing in non-native species that disrupt local life. In 2008, at Palmyra Atoll near Hawaii, iron from a shipwreck caused an increase in algae and a type of sea anemone, which covered and damaged coral, creating a "black reef."

Artificial reefs can quickly increase local fish and algae populations. However, scientists debate whether these increases happen because fish are drawn from nearby areas or because the reef itself supports more life. Some researchers argue that artificial reefs do not increase fish numbers but act like fishing tools that attract fish from other places. Others suggest artificial reefs can also create new life. A 2022 review said that whether artificial reefs support life or just attract it depends on each reef's specific situation and must be studied after installation.

Gathering fish in one place makes fishing easier. This can lead to overfishing and harm to fish populations, affecting both small-scale and large-scale fishing practices.

There are concerns that artificial reefs might be misused as a way to dump waste in the ocean. Rules have been created to prevent this, but they may not fully protect the environment.

Some artificial reefs are less stable than expected, breaking apart and becoming ocean waste. In the 1970s, waste tires were used to build artificial reefs, but tropical storms later caused the tires to wash onto beaches, damaging coral reefs and stopping new coral growth. At Osborne Reef near Fort Lauderdale, Florida, storms broke the straps holding tires together. By November 2019, 250,000 of about 700,000 tires had been removed. France has also started removing its tire reefs. The Ocean Conservancy now includes tire cleanup in its annual International Coastal Cleanup in September. Since 2021, 4Ocean has added tire removal to its cleanup efforts.

Some artificial surfing reefs have also caused problems. Early projects used sand-filled bags that broke down faster than expected. Examples like Pratte's Reef in California and Mount Reef in New Zealand required costly cleanup work. Some cleanup costs were higher than the original reef construction. Critics say this method of building reefs is flawed.

Artificial reefs, especially those made from materials not meant for the ocean, can break down and harm natural habitats. If the wrong materials are used, they might stop algae from growing, which is important for coral survival.

Materials like plastics, oil, paint, asbestos, and rusting metals can release harmful chemicals, such as PCBs and heavy metals, into the environment. These chemicals can enter the food chain and affect fish and humans. However, eating seafood from artificial reefs or shipwrecks is unlikely to harm humans at normal consumption levels, except for urchins and other shellfish that should be avoided.

International guidelines recommend using non-toxic materials for artificial reefs. The 2009 "Specific Guidelines for Assessment of Inert, Inorganic Geological Material" from the London Convention and Protocol/UNEP state that inert materials should not cause pollution through leaching, breakdown, or biological activity.

Scientists continue to test materials that can be safely used in artificial reefs. For example, oil and coal fly ash have been mixed with cement and lime to create experimental reef blocks. However, like tire reefs, these materials still raise concerns about possible chemical leaks.

In the United States, best practices for preparing ships to be used as artificial reefs include removing all harmful materials, such as PCBs, and ensuring the vessel is safe for divers. If removing harmful materials is too difficult, the EPA may allow it, as was the case with the ex-USS Oriskany.

Examples

Florida has many artificial reefs. Some of these reefs were made by intentionally sinking ships, such as Coast Guard cutters Duane and Bibb and the U.S. Navy landing ship Spiegel Grove.

In the early 1970s, over 2,000,000 used vehicle tires were placed off the coast of Fort Lauderdale, Florida, to form an artificial reef. However, the tires were not properly secured to the reef structures. Ocean currents broke them loose, sending them crashing into the developing reef and its natural neighbors.

Neptune Memorial Reef was originally planned as an art project called The Atlantis Reef Project. It was envisioned and created by Gary Levine and Kim Brandell. Burial at sea became a way of financing the project. As of 2011, about 200 "placements" had occurred. Cremated remains are mixed with concrete and either encased in columns or molded into sea-star, brain-coral, 15 feet (4.6 m) castings of lions or other shapes before entering the water.

In 1921, the U.S. battleship Massachusetts was sunk intentionally in shallow water off the coast of Pensacola, Florida, and then used as a target for experimental artillery. In 1956, the ship became the property of the state of Florida by the Florida Supreme Court. Since 1993, the wreck has been a Florida Underwater Archaeological Preserve and is included in the National Register of Historic Places. It serves as an artificial reef and recreational dive site.

The world’s largest artificial reef was created by sinking the 44,000-ton aircraft carrier USS Oriskany off the coast of Pensacola, Florida, in 2006.

The second-largest artificial reef is the USNS Hoyt S. Vandenberg, a former World War II-era troop transport that served as a spacecraft-tracking ship after the war. Hoyt S. Vandenberg was sunk seven miles off Key West on May 27, 2009, in 140 feet (43 m) of clear water. Supporters expected the ship to draw recreational divers away from natural reefs, allowing those reefs to recover from damage caused by overuse.

The ex-USS Spiegel Grove is located on Dixie Shoal, 6 miles (9.7 km) off the Florida Keys in the Florida Keys National Marine Sanctuary. Her location is 25°04′00″N 80°18′01″W / 25.06667°N 80.30028°W.

The ocean liner SS United States is currently planned to be sunk off the coast of Destin and Fort Walton Beach in Okaloosa County, Florida. Once sunk, it will surpass the USS Oriskany as the world’s largest artificial reef. It will be visible as high as 60 feet and as low as 180 feet, with its funnels removed. The SS United States is currently in Mobile, Alabama, to be stripped of any hazardous materials and valuable items.

In 1970, the Georgia Department of Natural Resources (DNR) began building a network of artificial reefs to provide habitats for game fish. Georgia generally lacks natural coral reefs because the ocean floor off the coast is too sandy and too low-sloping to promote coral growth. These artificial reefs attract a huge variety of organisms. According to a marine ecologist from Georgia Southern University, "the diversity rivals natural coral reefs."

L Reef was established in 1976. It is located roughly 23 nautical miles (43 km; 26 mi) east of Ossabaw Island and is 55–65 feet (17–20 m) below the ocean’s surface. It contains a variety of different debris, including New York City subway cars, M-60 tanks formerly used by the United States Army, and concrete culverts. In 2023, on December 21, the DNR unloaded two retired railcars from the Metro Atlanta Rapid Transit Authority. In August 2024, divers discovered soft coral growing on the railcars and counted nine species of game fish.

USS Yancey was sunk as an artificial reef off Morehead City, North Carolina, in 1990, as AR-302. It is lying on its starboard side at a depth of 160 ft (49 m).

USCGC Spar was scuttled in June 2004 by Captain Tim Mullane in 108 feet (33 m) of water, 30 miles (48 km) off Morehead City, North Carolina, where it serves as an artificial reef.

USS Indra was sunk as an artificial reef on August 4, 1992, in 60 feet (18 m) of water. Its coordinates are 34°33′55″N 76°58′30″W / 34.56528°N 76.97500°W.

USS Aeolus was sunk to form an artificial reef in August 1988 as AR-305. The ex-Aeolus is located 18.3 nautical miles from Beaufort Inlet Sea Buoy in 104 feet (30 m) of water.

In the late 2000s, the New York City Transit Authority decided to retire an outdated fleet of subway cars to make room for new R142 and R142A trains. The obsolete subway cars, nicknamed "Redbirds," had run on the A Division (former Interborough Rapid Transit Company routes) of the New York City Subway system for 40 years. Each car was stripped, decontaminated, loaded on a barge, and sunk in the Atlantic Ocean off the coasts of Delaware, Virginia, South Carolina, Georgia, and Florida. Some cars had number plates removed because of rust, which were then auctioned off on eBay. A total of 1,200 subway cars were sunk for this project.

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