Coral reefs provide a home for an abundance of animal and plant species, many endemic to the reef ecosystems. Corals also act as nurseries for many fish species, providing shelter and food. Reefs do not only benefit marine life, but also provide ecosystem services to humans, such as coastal protection from storms, and sustainable livelihoods to coastal communities through fishing and eco-tourism ventures. Despite their ecological and economic value, coral reefs are threatened worldwide by climate change and increased seawater temperatures, ocean acidification and destructive fishing practices. The global loss of coral reefs not only threatens marine diversity, but also human lives, as these ecosystems produce food and decrease poverty. Despite this grim outlook, all hope is not lost, and one possible solution is the construction of artificial reefs.

What are Artificial Reefs?

Artificial reefs are tools used by marine conservationists in an attempt to restore coral reef ecosystems. These artificial reefs are made from a wide variety of natural and synthetic materials, coming in all shapes, styles and sizes. The main goal of marine artificial reefs is to provide a stable surface for corals to grow on, as well as a habitat for fish and other organisms that would naturally occur on a reef. Artificial reefs have received a lot of praise across the world for their success stories. However, these artificial structures also receive a lot of criticism as they address the symptoms of coral reef decline, and not the problems causing this decline. Some artificial reefs are purposefully built structures made from PVC, steel or concrete, however others are man-made items that were sunk on purpose, like shipwrecks or construction debris.

The ecological structure, function and irregularity of surfaces of artificial reefs vary depending on the location and degree to which they mimic natural habitats. Some reefs are unintentional, such as the pylons of oil rigs. Artificial reef structures are usually placed in the open ocean with few features. These new structures act as a substrate for free-floating coral polyps to settle on, as well as the larvae of other species that have a sedentary phase. Eventually corals and sea sponges that occur naturally on reefs take over the artificial structure, and fish and other invertebrates are attracted to them, like they are to natural reefs.

The History Behind Artificial Reefs

Artificial reefs can be traced back thousands of years, from the Ancient Persians to indigenous cultures throughout the Indo-Pacific. Structures were initially used as Fish Aggregation Devices (FADs) to increase available habitat to fish, as a tool to help harvest more fish. A book written by John Holbrook in 1860 is the earliest known publication about how to use artificial structures to attract fish to an area that was damaged by development.

Charles Darwin is considered to be the first reef conservationist, as he attached corals to bamboo stakes to observe their survival. Although bamboo does not make for a very effective artificial reef (since it degrades underwater), it proved to be a good example of how artificial structures can be used to provide a safe substrate for corals to grow on.

Divers coming across long-sunken wrecks were probably the first to notice how artificial man made structures can be used by nature to create a thriving ecosystem. From those observations, conservationists realized that humans could improve the rate of recovery of coral reefs and other marine ecosystems by providing a structure that corals and sponges can latch onto.

Artificial reefs started being used in the 1970s for the restoration of coral reefs. During the next decade, a lot of structures that were readily available were sunk, like decommissioned ships, train cars and vehicles. If those structures were stable and non-toxic, they successfully created a habitat for corals and other organisms. This practice did receive public criticism, as it was seen by many as a means to dispose of waste. Some companies did in fact treat it as waste disposal, such as mixing industrial waste into the concrete used in the artificial reefs, dumping disused tires into the ocean, and attempting to use construction waste as reef substrate. These incidents set back the field of artificial reef building back many years.

Artificial Reefs Today

Luckily, scientists and marine biologists have learned a lot from these examples. Instead of using materials that would be considered waste, most artificial reefs are purposefully designed and deployed in specific areas, using non-toxic and long-lasting materials. Artificial reefs are designed with several goals in mind:

• Replacing structure and habitat diversity in places where this diversity has been lost due to dredging, development or storms.
• Increasing the size of existing reefs to enhance local marine resources and improve biodiversity.
• Create artificial reefs for tourism purposes to reduce the pressure on natural reefs.
• Create art-inspired reefs to increase awareness of coral reef decline to the public.

Artificial reefs will only work in waters that are conducive to coral growth. These artificial structures need to be used in conjunction with other conservation actions, such as establishing marine protected areas, reducing over-fishing and unsustainable fishing practices, and limiting land- and sea-based threats.

It is important to note that coral reefs are not the only types of reefs in the world. Other reefs, such as oyster reefs, can be artificially made using easy-to-come-by materials, such as oyster shells and oyster larvae (known as spat) to grow on cement and other loose materials.

Over the last few years, more and more novel methods and materials are being used to create artificial reefs, some of which show a lot of promise. This includes 3D printing technology, where printers are used to create structures with a large surface with structural diversity, which can not be achieved through natural means. For many years, artificial reefs were seen by many as “mindless meddling”. However, more and more studies are showing that if artificial reefs are combined with other conservation efforts, it will result in an integrative and holistic reef management program that will benefit thousands of marine organisms.