Making Artificial Reefs

Science is finding a way to build artificial reefs.

 Making Artificial Reefs

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• What reefs do: Natural reefs prevent billions of dollars a year of flood damage in coastal communities. Rising sea levels and increased risk of storm surges will require better sea defences in the future. Rather than blocking waves, as a sea wall does, a reef slows them, dissipating their energy before they reach land. But while natural reefs take centuries to grow, hybrid versions can be conjured up in months.
• What are reefs: A reef is a ridge of material at or near the surface of the ocean, and can occur naturally. Natural reefs are made of rocks or the skeletons of small animals called corals. Reefs can also be artificial, made by human beings.

1. Types of natural reefs: The four main types of coral reefs are fringing reefs, barrier reefs, atolls, and patch reefs. The most common type is the fringing reef, which grows seaward directly from the shore. They are separated from the shore by narrow, shallow lagoons.
2. Coral reefs protect coastlines from storms and erosion, provide jobs for local communities, and offer opportunities for recreation. They are also are a source of food and new medicines.
3. Now, technicians are putting up artificial coral reefs which co-opt the local ecology to help out. Fully grown, they will be a defence against erosion and wave damage—and a tourist attraction for divers.

• How to make: In the 1970s Wolf Hilbertz developed a technique that uses submerged electrodes to run electrical currents through seawater. This precipitates calcium carbonate and magnesium hydroxide out of the seawater, forming limestone similar to that of natural reefs. The artificial reef can become the substrate upon which a natural coral ecosystem develops.

1. The original idea was to stop at the limestone stage, growing structures underwater, some of which would be used in situ as things like port facilities, while others would be hoisted ashore as buildings. It looked like a simple, low-cost alternative to making things out of concrete.
2. In 1996 the Global Coral Reef Alliance began using Biorock for reef repairs by growing a six-metre structure in the Maldives. Other repairs have followed in Indonesia, Jamaica and Mexico. The Pemuteran Coral Reef Restoration Project, in Bali, is more than 300 metres long and includes dozens of “nurseries” in which Biorock acts as nuclei for the natural extension of the reef.

• DARPA swoops in: The research agency run by America’s Department of Defence, DARPA, also sees hybrid reefs as a means of coastal defence—in this case protecting the country’s seaside military installations. This is the “Reefense” project, the goal being a hybrid reef-type system which will be maintenance-free and self-repairing. Reefense therefore involves not only creating reefs and measuring their effectiveness, but also attracting and fostering appropriate organisms to sustain the reefs’ health, ensuring they can survive even when natural reefs are suffering.
• Oyster reefs: Though coral reefs thrive in warmer waters, oyster beds are likely to form the best basis for reefs in cooler areas. Oyster reefs form when layers of old oyster shells fuse together under the weight of their successors above, producing large, solid structures. Such reefs were abundant in the waters off north-east America until overfishing and environmental degradation destroyed them. But they can be built on the same artificial foundations as hybrid coral reefs, and should provide similar protection.

1. Whichever reef-building organism is involved, though, a thriving hybrid reef needs to attract the right additional inhabitants.
2. Algae can compete for space with the reef-building anthozoans, and that some types of fish will nibble at the reef itself.
3. But other fish eat algae and drive off predators. She says that a variety of techniques might be employed to attract beneficial species.

• Challenge: Hybrid reefs will have to survive climate change, which is making seawater both warmer and more acidic. Both trends can damage corals.
• EXAM QUESTIONS: (1) Explain how technical endeavours to build artificial reefs will protect local communities. (2) Explain how science can ensure that artifical reefs stay "alive" for long, in face of climate change.

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