GCRA
OVERVIEW
FAQ
NEWS
ARTICLES
PHOTOS
REEF ISSUES
RESTORATION
PAPERS
LINKS
|
|
|
|
Third Generation Artificial Reefs Wolf Hilbertz and Thomas Goreau (Submitted to Ocean Realm magazine, October 1997) NOTE: This paper describes the different types of artificial reefs, and explains how the newly developed mineral accretion technology builds artificial reefs which are intrinsically superior to all other methods in terms of biological restoration and structural stability. The first artificial reefs on record were made in the early 1800's in Japan from sticks of bamboo. Since the early 1950's marine fishery interests have been investigating the use of artificial reefs for manipulation of fish populations, utilizing concrete rip-rap, natural stone, bricks, and a plethora of other materials. All too often, and persisting to this day, these installations furnished a welcome excuse to discard unwanted artifacts and civilization's refuse like automobile tires, cars, ships, planes, streetcars, tanks, and offshore hydrocarbon platforms ('rigs for reefs') for economic gain with little or no regard for marine ecology; in the 1960's and 1970's power companies even sponsored R&D for the utilization of highly toxic fly ash in artificial reef components. These agglomerations of refuse often leach dangerous chemicals, decompose and dissipate quickly, and at best function as fish aggregation devices. We call these reefs of the first generation. During the last two decades Japanese agencies and companies in particular have adopted more sensible approaches to reef building with the primary objective to increase yield of protein in relatively barren coastal seas. It has been proposed to install specially engineered devices as management tools for the cultivation of fish, bivalves, and crustaceans in hundreds of bays and estuaries along the coast. Even fish- and invertebrate-specific reefs were developed. The preferred construction materials are various kinds of plastics, sometimes reinforced with fiberglass, concrete made with hydraulic cement, and steel. These structures are vastly improved versions of their predecessors. Together with efficient anchoring techniques they represent in expert and public view alike the state-of-the-art of reef building, the second generation. Their purpose ranges from fish aggregation devices to mariculture pens, from providing diving sites for sport divers to environmental mitigation and restoration. Yet, their inherent limitations prevent them from even remotely approaching the wonderful manifold functions of coral reefs, the most intricate and productive marine ecosystems. The vast majority of artificial reefs we know are biologically impoverished and generally do not produce genuine growing coral reef communities. Rather than organically becoming part of the marine environment, these structures will always remain foreign objects, and sometimes transform into dangerous projectiles in storms. For instance, after hurricane Andrew hit Southern Florida, a survey of artificial reefs in the area revealed that not one remained intact. All had moved, and while from one to many fragments were found, many vanished entirely. Global sea level rise of around 2 millimeters per year, marine pollution and over-fertilization, mining of coral rock and sand, damage inflicted by dredging, net, dynamite, and spear fishing, the tropical species aquarium trade, and activities by sport divers have combined to cause ever greater damage of coral reefs; recent reports point to increasing bacterial and fungal diseases attacking corals. As sea level rises and reefs deteriorate, coastal areas lose their natural protection, resulting in beach and land erosion as well as salt water intrusion of aquifers. At risk of inundation are all the great and fertile river deltas, vast stretches of coastal land and all low-lying islands. Entire island states will be washed down in size and, as extreme weather conditions are augmented further, gradually or suddenly vanish beneath the waves. Irreplaceable cropland will be lost and hundreds of millions of lowlanders will be forced to seek higher ground. Example given: the Maldive Republic in the Indian Ocean. Situated on about 107,500 square kilometers of archipelagic ocean floor which is part of a subsiding tectonic plate, it is comprised of about 1,200 small coral rock islands. Slight to severe coastal erosion is evident on most islands. Mining of fossil and live coral as well as sand for construction and beach fortification is widespread. The reef formerly protecting the southern coast of the capital island Male was mined out, leading to severe flooding a number of years ago. Now concrete tetrapods, being installed along the entire southern flank of Male and costing more than US$ 8,000 per meter of shoreline, hopefully will help to avoid future disasters. Huge quantities of coral reef rock, sand, and aggregates, which until then had a vital role in supporting biodiversity, have been worked into these ungainly structures using imported hydraulic cement, whose production contributes vast amounts of the greenhouse gas carbon dioxide to the atmosphere, aggravating the problem of sea level rise even further. We have developed a novel technology called "mineral accretion" which uses electricity to "grow" limestone rock on artificial reef frames and increase growth rates of corals and other reef organisms: two electrodes, supplied with low-voltage direct current, are submerged in sea water. Electrolytic reactions at the cathode (negatively charged electrode), cause minerals naturally present in sea water, primarily calcium carbonate and magnesium hydroxide, to build up. At the same time a wide range of organisms on or near the growing substrate is affected by electrochemically changed conditions, shifting growth rates. Reefs of any configuration and size can be grown for purposes of reef restoration and shore protection. We chose the term 'third generation reefs' because these have little in common with their predecessors. Rather than being mere agglomerations of deteriorating shapes they are growing life support systems, bringing about rich and beautiful ecologies. Mineral accretion technology is unique because: 1. It is the only method that produces natural limestone which also constitutes coral skeletons, reefs, and sand. 2. Young corals and other marine organisms readily settle on the substrate. 3. Naturally settled corals, attached corals, coralline algae, bivalves, and a host of other organisms grow at exceptionally fast rates. 4. Rapid growth of calcareous algae supplies sand for beach nourishment. 5. These artificial reefs allow corals on them to thrive even when water quality conditions have deteriorated to the point of killing surrounding corals. 6. As the reefs grow they cement themselves in place, be it to the sea floor or vertical rock or coral formations, contributing to permanent shore protection. 7. Should damage be inflicted to these structures, renewed application of electricity readily facilitates repair. 8. Reefs can be grown and maintained utilizing direct or indirect solar irradiance converted by photovoltaics, wind turbines, ocean thermal energy plants and those working with saline gradients, ocean currents, and waves. Thus release of greenhouse gases from burning fossil fuels for generation of electricity and for chemical decomposition of calcareous raw materials for cement production can be avoided. 9. Artificial or natural components of accreting structures can be harvested in controlled, sustainable ways to provide building materials for terrestrial use in regions which have to import aggregates and cement. 10. Hydrogen gas, bubbling from the cathode, can be collected for use as a non-polluting energy carrier. Third generation reefs have been grown using shore power, wind-driven generators (Photo 1), and photovoltaics (Photo 2) in Texas, the U.S. Virgin Islands (Photo 3), Louisiana (Photo 4), California, British Columbia, Cayman Islands, Mexico, Colombia, Venezuela, the Turks and Caicos Islands, Jamaica (Photo 5,6), Panama, Japan, Corsica, on Saya de Malha Bank in the Indian Ocean, the Seychelles (Photo 7), and the Maldives (Photo 8,9). Most of these are smaller pilot projects, up to 5 meters tall and up to 15 meters across, submerged in water 1 to 14 meters in depth. Much larger reef systems, up to 630 meters in length and up to 20 meters wide, are in the planning stages. By placing negatively charged materials like wire mesh, wire, chains, and conductive polymer formations in conjunction with anodic material on or around coral formations growing at their original site, renewed growth and restoration can be facilitated. This method of cathodic reef stimulation (CRS) is currently being investigated at various locations under differing conditions. In the course of projected global warming many regions of the world ocean gradually or rapidly may become suitable habitats for reef-building corals. Other areas, hitherto offering the right conditions for coral growth, may become too hot or cold to sustain reef builders and their ecologies. In this scenario, although replete with incalculable uncertainties, solar-based third generation artificial reef technology could play a crucial role by helping to preserve marine biodiversity, facilitating effective shore protection, providing ecologically sound building materials, and even contributing to solution options towards global climate stabilization. Captions for photographs 1. Wind-driven turbines on a previously damaged part of the fringing reef. St. Croix, USVI, 1976. 2. Photovoltaic rack being installed at the north coast of Jamaica, 1994. 3. Accreting reef in St. Croix, 1976. 4. Detail of a reef grown in the Mississippi Delta in brackish water, 1986. 5. Coral growing on accreted substrate of a reef in Discovery Bay, Jamaica, 1992. Initially fist-sized, the coral grew to the size of a football within one year, although corals in the vicinity were increasingly killed by deteriorating water quality. 6. One of three identical reef frames established 1993 near Negril, Jamaica, with attached and naturally settled corals. Submerged floating objects repeatedly damaged the mineral substrate, causing it to fall off. Application of electrical current immediately began to facilitate repair. An identical control structure with attached corals but receiving no electricity rusted away in a matter of several months. 7. Newly established reef in the Seychelles, 1997. 8. Artificial reef in the Maldives started in 1996, its spiny legs attaching the structure by mineral accretion firmly to the sea floor. 9. Close-up of the upper part of the reef. Dozens of corals belonging to different species thrive on the growing framework. Acknowledgement We thank the following persons for their active help and support during the past four years: Carlos Alberto Arango, Ceylon Clayton, John Collie, Fritz Dressler, Gabriel D'Espaigne, Gafoor, Graemme Gavin, Maya Goreau, A. Azeez A. Hakeem, Carlos Henrique Hernandez, Derrick Hilhertz, Kai Hilbertz, Maizan Hassan Maniku, Philippe Michaud, Caroline Mekie, Ahmed Mujuthaba, Frank Reidock, Ursula Rommerskirchen-Hilbertz, Shah, Joel Souyave, Angel Tribaldos, Bill Wilson We are grateful for support received from the Negril Coral Reef Preservation Society, Freundeskreis der Hochschule fur Kunste Bremen, and the European Union. Anodes were donated by Heraeus Elektrochemie GmbH, Germany.
|
|