Artificial reef

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Construction in place of an artificial reef from concrete block
Construction in place of an artificial reef from concrete block
Tires being placed in an array to determine their effectiveness as habitat for fish.
Tires being placed in an array to determine their effectiveness as habitat for fish.

An artificial reef is a man-made, underwater structure, typically built for the purpose of promoting marine life in areas of generally featureless bottom. Artificial reefs may also serve to improve hydrodynamics for surfing or to control beach erosion.

Artificial reefs can be built in a number of different methods. Many reefs are built by deploying existing materials in order to create a reef. This can be done by sinking oil rigs (through the Rigs-to-Reefs program), scuttling ships (such as the USS Oriskany), or by deploying rubble, tires, or construction debris. Other artificial reefs are purpose built (e.g. the enormously successful and effective reef balls) from PVC and/or concrete. Historic or modern shipwrecks become unintended artificial reefs when preserved on the sea floor. Regardless of construction method, artificial reefs are generally designed to provide hard surfaces to which 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.

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[edit] History

The construction of artificial reefs is thousands of years old, although the historic usages were related to sea power rather than aquaculture. Ancient Persians blocked the mouth of the Tigris River to thwart Indian pirates by building an artificial reef,[1] and during the First Punic War the Romans built a reef across the mouth of the Carthaginian harbor in Sicily to trap the enemy ships within[2] and assist in driving the Carthaginians from the island.

The use of artificial reefs to increase fish yields or for algaculture also has a long history. During the 1600s reefs of building rubble and rocks were used in Japan to grow kelp,[3] while the earliest recorded construction of artificial reef in the United States is from 1830s when logs from huts were used off the coast of South Carolina to improve fishing.[4]

In the early 1970s, a series of thousands of disused vehicle tires were dumped off the coast of Fort Lauderdale, Florida to form an artificial reef, causing environmental problems over time. See Fort Lauderdale tire reef.

[edit] Artificial surfing reefs

Man made objects provide hiding places for marine life, like this Sarcastic fringehead
Man made objects provide hiding places for marine life, like this Sarcastic fringehead

Artificial surfing reefs have been created for surfing, coastal protection, habitat enhancement and coastal research. The world's first attempt was made in El Segundo, near Los Angeles, in California. The next attempt was at Cables Stations Beach, Perth, Western Australia. This reef was constructed of large granite rocks placed in a pyramidal shape to form an appropriate breaking wave form that would suit surfers. An artificial reef constructed of over 400 massive, geotextile bags (each one larger than a bus) filled with sand was constructed in 2000 at Narrowneck on the Gold Coast of Queensland, Australia. This artificial reef had two objectives: stabilizing beach nourishment and improving surfing conditions. Initially the structure produced some exceptional surfing conditions, however settlement of the geotexile sandbags, as well as huge differences between the design and final reef shape means that the surfing has only been moderately improved.

Artificial surfing reefs typically resemble a "submerged breakwater", and proponents have suggested additional benefits beyond improving surfing conditions. In Hawaii and California, long stretches of coast are subject to powerful waves that crash directly onshore. An artificial reef situated 150-300 yards offshore might not only create surfing opportunities but, by dissipating wave energy before it strikes the shore, create safer swimming areas and reduce coastal erosion.

The USS Spiegel Grove was sunk in 2002 to make an artificial reef. In United States, in particular, complex coastal permitting requirements combined with environmental opposition provide a major obstacle to building surfing reefs. As of February 2006, the only reef built in the U. S. specifically for surfing purposes is "Pratte's Reef" in southern California. Artificial reefs built for enhancement of marine habitat face far less environmental opposition, in part because they are located in much deeper water some distance offshore. A number of such man-made reefs exist off of Florida and in Hawaii.

[edit] Mineral accretion

Artificial surfaces are being grown using a process called mineral accretion. In mineral accretion, a low voltage current is applied to a metallic structure to cause limestone to accrete or build on the surface, upon which coral planulae can attach and grow. This greatly speeds the coral growth process on artificial surfaces. The voltage is low enough that it can be generated by floating solar panels or from wave motion.

A coalition of scientists known as the Global Coral Reef Alliance (GCRA) has been developing a technique called the Biorock Process using mineral accretion for reef restoration, mariculture, and shore Protection.

[edit] Environmental concerns

The multi-million-dollar cleanup of Osborne Reef, a tire dump near Fort Lauderdale, Florida, has prompted questions about the risks of creating artificial reefs. In Florida, the tires posed a particular threat after breaking free from their restraints. The tires then migrated shoreward and ran into a living reef tract, climbed up its slope and killed everything in their path. According to The Ocean Conservancy, a Washington-based environmental group, the Florida reef may be an indication that the benefits of artificial reefs need to be re-examined. Jack Sobel, a senior scientist at the group, has said "There's little evidence that artificial reefs have a net benefit."[5]

[edit] Footnotes

  1. ^ Thomas Wayne Williams, A Case Study of Artificial Reef Decision-Making in the Florida Keys, Virginia Commonwealth University [1] Last accessed 20 December 2006
  2. ^ Ron Hess, Denis Rushworth, Michael V. Hynes, John E. Peters, Disposal Options for Ships, Chapter 5, "Reefing," Rand Corporation, [2] Last accessed 20 December 2006
  3. ^ Fisheries Technologies for Developing Countries, National Academies Press [3] Last accessed 20 December 2006
  4. ^ Gulf States Marine Fisheries Commission, GUIDELINES FOR MARINE ARTIFICIAL REEF MATERIALS, [4] Last accessed 20 December 2006
  5. ^ Florida Raises Ill-Fated Artificial Reefs

[edit] See also

[edit] External links