Coral aquaculture, also called coral farming or coral gardening, is the process of growing corals for commercial use or to help repair damaged coral reefs. This method helps protect young corals when they are most likely to die. Small corals are grown in special nurseries and later placed back onto the reef.

Scientists also grow corals for research, businesses use them for selling live or decorative corals, and some people keep them in home aquariums.

Coral farming begins by taking a piece of a coral colony or tiny coral babies from a reef. These are grown in a nursery until they are strong enough to be planted back on the reef. This method is often called the "gardening method" and is similar to tree farming, which also mimics natural ecosystems.

Adult corals can be moved to a reef, usually in areas that have been damaged. Coral farming is used to help protect reefs in countries like the Philippines, Israel, Solomon Islands, Palau, Fiji, Marshall Islands, and Japan. In North America and Europe, corals are also farmed in public aquariums on land.

Benefits of healthy reefs

A healthy reef has many different types of plants and animals, including many kinds of corals. It needs herbivores, such as parrotfish and collector urchins, to eat algae that grow too much. Most corals need water that is clear and has few nutrients. Corals get food from zooxanthellae, which are symbiotic algae, as well as from plankton and tiny floating particles. Zooxanthellae need a mix of white and blue light to grow inside the coral, depending on the type of coral. Some corals, like the orange cup coral, do not need light and instead get food from plankton or floating nutrients.

Coral reefs help protect coastlines from erosion and storm damage. They are important foundation species that support many other sea life by providing homes and nursery areas for nearly one-third of saltwater fish species. These include 10% of all fish caught by humans for food, even though coral reefs cover less than 1% of the ocean’s surface.

Reefs in decline

Coral reefs are harmed by many factors, such as strong weather events like cyclones, water temperatures that are 1–2 degrees higher or lower than normal for several weeks, predation by crown of thorns starfish, and competition with other important species like algae for space. Algae can grow too much in coral reef areas when water has too many nutrients, such as nitrogen and phosphorus, or when there are not enough herbivorous fish to eat the algae because fishing has reduced their numbers.

Corals can remove algae from their surfaces using their polyps. However, when corals are in poor conditions, they struggle to protect themselves from algae, diseases, and other problems. This use of energy for survival instead of growth puts corals at risk. Coral bleaching happens when corals lose their vital zooxanthellae, which can be caused by any of these stressors. Corals push out their symbionts to remove sources of stress. Corals can live for up to one week without zooxanthellae, but this is very difficult. Corals may recover from bleaching and regain zooxanthellae if conditions improve and stressors decrease.

Natural challenges to coral reefs are made worse by human activities. Human-caused stressors, such as runoff, coastal development, dynamite fishing, cyanide fishing, overuse of resources, and marine pollution, threaten 58% of the world’s reefs as of 2009. For example, in Indonesia, mushroom coral is harvested to provide materials for jewelry and souvenirs. The removal of living reef organisms, including coral, is increasing globally. Coral is often overharvested to meet growing demand. Overharvesting weakens reefs’ ability to recover after other harmful events.

Reef restoration

Coral propagation can help increase the amount of coral, the variety of life on a reef, and the different ways the reef is built. Success has been seen with fire coral, Pocillopora verrucosa, and Acropora hemprichii. A restored reef supports animals that live on the reef, like reef fish.

Reefs are fragile and complex ecosystems. It is hard to recreate how a reef looked before it was damaged. Most coral farms used to help fix damage can only grow fast-growing corals that are easier to care for. Slow-growing corals are costly to grow and are not fast-growing, which is important when damage happens. Most coral reefs may take many years to return to their original condition. Corals grown in nurseries help reefs stay strong by adding young coral animals to the environment. This could help new corals grow if the transplanted corals are placed just before young coral animals are released into the water.

Oceanographer Baruch Rinkevich created the term "active restoration" to describe growing corals in farms, compared to "passive restoration" methods that focus on reducing harm by actions like creating marine protected areas (MPAs). Coral reefs are often placed in MPAs to help them recover by limiting human activities.

Aquarium trade

Many people like to create coral displays in their home aquariums. To meet this need, businesses raise coral in special farms. Some companies grow coral in sunlit greenhouses rather than using artificial lights in aquariums. At the 1999 Hawaii Marine Ornamentals Conference, experts recommended giving top priority to projects that improve the raising of marine ornamental corals and protect coral reefs. They emphasized the importance of encouraging hobbyists to buy coral only from farms to reduce the taking of too many corals from the wild. They also suggested efforts to teach consumers that corals raised in farms are a more sustainable and better choice than corals taken directly from reefs.

Methods

The process of farming for reef restoration includes several steps: collecting coral polyps or larvae, growing them in tanks, moving them to sea nurseries for more growth, and then re-transplanting them onto the reef.

Coral can reproduce without sex by budding or with sex by spawning.

Collecting coral polyps from existing reef colonies or fragments can happen at any time. Common targets include branches, fragments, or branch tips. This is the most commonly used method.

Collecting coral spawn usually happens once a year, right after a spawning event. Coral colonies on a reef often spawn together in a synchronized event on a specific day. This allows scientists to collect hundreds of thousands of coral embryos at one time. This method is called spat stocking.

At the Great Barrier Reef Aquarium in Townsville, Australia, large colonies of Acropora formosa have special devices placed above them during spawning. Small mature colonies are moved from the reef into tanks to spawn. Afterward, they are reattached to the reef.

Using this method, the parent coral colonies are not harmed. This method has also been proven effective on Red Sea soft coral species, including Alcyonarians: Clavularia hamra, Nephthea sp., and Litophyton arboreum.

Linden describes an apparatus made of Petri dishes lined with preconditioned Mailer's paper disks, where the planula of Stylophora pistillata are grown. One-month-old survivors are moved onto plastic pins in a mid-water coral nursery. The trays are covered with fitted plastic nets to prevent predation and detachment. After four months, more than 89% of the corals survived.

Next, the corals are moved to floating nurseries in the sea. They float in the water column, attached to a submerged structure. Some experts suggest placing them at a depth of 6 meters to ensure they receive the right amount of sunlight. They are fixed to an artificial substrate, usually made from string, wire, mesh, monofilament line, or epoxy. The colonies stay there for 8 to 24 months to grow large enough for transplantation back to the reef.

When the corals are large enough for transplantation, they are secured to plastic pegs, masonry anchors, or directly to the reef base using epoxy.

For commercial markets, the process is similar, but ocean cultivation continues until the colonies reach a marketable size (about the size of a fist). The final step involves extracting and packaging the corals for sale.

Coral Nurseries

Coral nurseries are created by taking pieces of coral and moving them to man-made structures to help build a coral reef. This allows scientists to choose which corals are included in the reef based on their ability to survive and their importance for future growth.

The National Oceanic and Atmospheric Administration (NOAA) worked with engineering students to create a different type of nursery that focuses on saving whole coral colonies. This method has shown positive results.

Most coral nurseries are either in the ocean or on land. Coral pieces are usually taken from living corals through a process called fragmentation, which allows them to grow into new corals in other areas. These pieces are placed on structures like trees or lines to help them spread out and grow.

Coral nurseries often help corals grow better and survive longer in the early stages compared to corals that are not in a nursery. Studies show that fragments of two non-branching Pacific corals survived better in nurseries than when planted directly on reefs. However, this advantage disappeared when nursery-grown corals were moved to the reef with other corals.

Laughing Bird Caye in Belize is an example of a coral nursery in the ocean. Hurricanes and coral bleaching are major problems in the area, so caretakers focused on planting corals in less stressful areas. When the corals grew large enough, they were moved to the main reef.

A total of 82,879 corals have been planted in the park, and the amount of coral cover has increased. However, funding and time are still challenges for the work.

In Guadeloupe, France, scientists designed a system to help ships anchor without harming corals. After six years, 52% of local coral species had grown on the eco-mooring blocks, even though the blocks covered only 300 square meters in the bay.

In Okinawa, Japan, scientists focused on growing coral seeds in nurseries, in addition to planting corals directly. These seeds were collected from other reefs through asexual reproduction. However, this method was not very cost-effective, even though it helped some areas.

To increase genetic diversity, scientists used donor corals to expand the gene pool for out-planting in Okinawa. While the success of these projects is uncertain, they have strong public support.

The Great Barrier Reef (GBR) is the largest and most famous coral reef, but it faces similar challenges. Coral nurseries in the GBR show variable results depending on the type of coral and environmental conditions. However, overall, they grow at the same rate or faster than natural reefs. Scientists believe that using nurseries to grow corals can help protect high-value tourism areas in the GBR, provided the costs of maintaining the nurseries stay low.

Economy

Coral aquaculture provides new ways for people living near reefs to earn a living. This is especially helpful in areas where fishing or collecting sea life is no longer possible, such as in Indonesia. Coral can be used in ways that protect the environment. Many coral reefs are found in areas with few resources. Raising corals needs simple and inexpensive materials, which makes it possible for communities with limited supplies. New methods, like placing coral baby corals on concrete blocks, help lower costs and save time compared to older methods.

History

One of the earliest serious efforts to grow coral outside of its natural environment happened at Nouméa Aquarium in 1956. At that time, many people in Germany enjoyed creating small reef setups at home. In the 1960s, growing coral for sale started in America. The hobby of keeping coral became popular in the early 1980s, partly because of magazines about aquariums.

In 2009, the US government gave $3.3 million to a project aiming to grow 5,000 groups of Acropora coral. Scientists said that moving 35 groups of coral each year could help restore coral numbers to levels seen in the 1970s within 10 years.

Research and development

Coral aquaculture helps scientists learn about how corals grow and live. Petersen found that young corals that reproduce sexually grow bigger when they are fed baby brine shrimp. This finding might help reduce the time it takes for young corals to become strong enough to survive in a hatchery.

The Mote Marine Laboratory maintains several groups of parent corals at its Tropical Research Laboratory. According to the laboratory’s website, these corals are grown from pieces saved after boat accidents and other environmental damage. The corals in the broodstock reserve are used to create fragments for restoration projects. Research is conducted to find the best size, shape, and time of year for restoring coral populations.

Market

Indonesia and the Philippines provide about 85% of coral reef products. Indonesia requires 10% of its coral production to be transplanted into the ocean. In 2012, most coral imported to the United States came from the wild, though more and more was grown in controlled environments. Between 1990 and 2010, coral imports to the United States increased by about 8% each year. After 2010, imports decreased because of the Great Recession and because more coral was produced within the United States. Trade in stony and reef-building corals is managed by the Convention on International Trade in Endangered Species (CITES). In Indonesia, most coral production happens near airports to make shipping faster.