| Author | Cynthia Warzecha, partial translation, |
|
| Date | 1999 | |
| Nature | Internet article | |
| Key words | reef balls coral ecosystem artificial reef |
A new technology for the artificial reef construction besides Atlantic
Author Cynthia Warzecha, partial translation,
Date 1999 Nature Internet article Key words reef balls coral ecosystem artificial reef
Lare ecosystems récifaux endured a big variety of changes anthropiques since several decades. The activities of recreation in sea (pleasure, fishing of leisure, diving), the silting up following the construction of works on the sea, the pollutions by the worn-out waters, the excessive arrival of nourishing salts as the nitrates or the phosphates, the thermal pollution and the overfisching contributed to the bad health of a lot of recifal ecosystems . The diving autonomes,les apnéistes and boats with their anchors can damage the coral ecosystems extensively. The overfisching of fishes eating algaes can entail in return a development accelerated of these that will end up choking the corals. The anthropic changes contributed to the loss of ten percent of the reefs coralliens of the world and two thirds supplementary risk to decline sèrieusement in the next years. Zoologist Maflorie Reakea-Kudla (1996) foresees the loss of seventy percent of the coral reefs of the world by the year 2036.
Various techniques have been used to create some habitats for organisms normally living in the reefs. In inshore waters of the United States, most efforts concentrated on the possibilities to increase the densities and the number of fishes in order to encourage the activities of diving and fishing of leisure. Of the actions as the iimersion deliberated of boats or platforms of boring of oil showed their efficiency in the increase of the local stocks of fishes.
However, he/it is again little certain that these structures really encourage some phenomena as the reproduction of fishes. He/it is in any case clear that they have a role of concentration of the piscatorial populations coming from common zones.
Thick efforts have been made for the restoration of the coral reef ecosystems. Of all marine ecosystems, the reefs coralliens is the more rich and complex of part the diversity of the relations trophiques of which they are constituted. The natural reefs are manufactured by symbiotic animals who associate to algaes intracellulaires specialized named " zooxanthelles ". By photosynthesis, these algaes produce sugars to short chain and the starch.
In return for these energizing molecules, the corals provide a part of nitrogen and the phosphor that they get while capturing some organisms microscopic planctoniques. Some coral species produce skeletons of calcium carbonate. The accumulation of these skeletal structures forms the coral reef.
Every coral species has its own fashion of growth. Some produce the branched out structures while others rather give some shapes rounded alike to half spheres. The concretions coralligènes provides the necessary habitats to a varied ecosystem that includes a number raised of species of fishes, crustaceans, invertebrates, and other marine organisms.
The first big artificial reefs to the world were the flowed involuntarily boats. Then one flowed, this time of purposeful manner of other boats, of the military tanks, a Boeing 707, of the cars found in the breakings, of the tires attached between them and of other unused materials. These first artificial reefs were put in place on the coast is and Southeast of the States Unis. The procedures of immersion for the construction of these reefs change according to the types of matters employees. Boats, tanks, planes and cars are emptied of gas, oil, and the other potentially polluting fluids. Broadly speaking, the motor and all light materials are also removed. The abduction of brass, generally found in the boats, is important because this alloy of metals is especially poisonous for some marine organisms. The immersion of the boats is usually gotten with the help of explosives. The boats are transported with tugs in the site targets the explosives then are triggered. Some floating barges are used to transport the cars and other materials on the site of the artificial reef.
Des old tires have been used like artificial reefs to the large of the coasts of Virginia of the North and Carolin of the south and Florida. One of the biggest reefs constituted of tires, the reef of Osbome to the large of the coast of Florida, nearly contains two millions of tires. An essential part of the preparation process resides in the perforation of the tires what annuls their floating.
Goodyear developed a device permitting the perforation of the tires on three zones of the circumference lately. After the tires have been stamped they are gathered by packets of ten to twelve and bound between them while using ropes of nylon. If the site of the artificial reef is topic at the stormy times or to the strong currents, the tires must be filled of cement. The boats or the barges can be used to put down the tires. Of advantage of fishes are attracted toward the reefs if the packets are stacked one on the other.
The platforms of oil are a possible artificial material whatever controversial for the realization of artificial reefs. A decline in the boring of oil in the Gulf of Mexico entailed the setting to disposition of a bigger number of platforms. Before the oil platforms can be converted in reefs, they must be beforehand cleaned very scrupulously. Some explosives are used then to destroy the " legs " and to sink the platform. These explosions can have potentially ominous effects on the plants and the animals who already settled on the terrific structures.
A relatively recent development (1993-94) in the artificial construction of reef is the use of structures made of concrete prefabricated named ReefBallses. These structures in the shape of hollow dome look like the reefs of corailproduits by some species of madréporaires. They possess different size holes that allow fishes and other marine organisms to penetrate inside.
The holes are conceived to create a streamlined whirlwind effect that nourishes in water and in nourishing particles the spineless colonizers. The concept of reef in the shape of ball punched watch that the profile of half sphere is not sufficient alone to assure the establishment of a food chain. The surfaces need current and light to function.
The half spheres are achieved while sinking the concrete in a mold of fiberglass that contains an internal and inflatable flexible reservoir. The holes are achieved thanks to the disposition of small balls of baudruche between the mold of fiberglass and the inflatable flexible reservoir. The concrete can be poured then. The flexible reservoir inside the half sphere is often used like device of floating during the setting up of the reefs. The ReefBalls are available in a certain number of sizes. The necessary total time to the manufacture of a ReefBall is of thirty minutes to one hour and half according to the size of the ball.
Nearly all types of concrete are usable in the construction. However, some additives must be incorporated that will reinforce the resistance of the half - spheres and will return them biocompatibles. Indeed, the plain concrete is to an elevated level pH because the hydroxide of calcium that it contains is basic. The addition of microsilicate brings back the pH to about to 8,3, that are the middle value of the sea water and reacts with the hydroxide of calcium. The compound that results some is then highly resistant and reaches a life span of at least five hundred years. Without available microsilicate, the half spheres must be soaked in the soft water during three at six months to make disappear a part of the poisonous calcium hydroxide for some marine organisms. If the ReefBallses are not treated, the only organisms resist the raised pH will colonize the ReefBall first and will prevent later by competition the other organism installation even though the pH had the time to become again normal.
Several different outside textures can be used for the ReefBallses that will especially encourage the navy species colonization by recruitment of the larvas planctoniques.
Several methods can be used to transport on marine site the ReefBallses. The flexible reservoir can be maintained swollen inside the half sphere and can be used like device of floating permitting the tow by boat. When the site has been reached the flexible reservoir is deflated and retired. The divers can accompagnéer the setting up of the reef while controling the coming down and the positioning. The use of the divers can permit to reduce to the minimum the destructions on the normal parts of the reef.
Some reefs can also be put in place without divers. The ReefBallses are conceived to remain steady once they were set down to the bottom. The shape of dome of these artificial reefs is the key of their stability. More than 50% of the mass are present under the median line. The over some dome is open to reduce the effects of uprising due to the action of the waves by stormy time.
The size of the Ballses reef can be personalized to satisfy the demands esthètiques and environmental. For example the mass of concrete can be doubléepour to satisfy to conditions with elevated hydrodynamisme.
ReefBallses proved to be very resistant to stern climatic conditions as for example the hurricane of 1995. The one reversed none of the ReefBallses here whereas the other artificial reefs of the zone have for most been destroyed or
The success of the artificial construction of reef depends on the goal of the project. The reefs constructed with materials of fall frequently answer the objective to attract fishes. A survey, undertaken close to the island of Marco, Florida, in 1972, concluded to meaningful increases of the quantities of fishes after the installation of a reef makes old air. Before the reef of tire has been constructed the staff of the navy ecology station applied of Marco fished on the zone sensed for the future artificial reef. The rate of capture was roughly of 0,5 fishes per hour. An investigation of follow-up has been driven several years after the setting up of the 100 000 tires. The rate of capture had increased a factor twelve.
Although the reefs constructed with materials of fall attract fishes in general, they are not favorable to the coral colony establishment. It is in particular true for the tires. For the reefs of metallic nature, they end up oxidizing and fall apart dragging the biophysical structure rupture and their decline for lack of even available surface. The corals never reach their natural size that is gotten for colonnies of more than hundred years.
