You are diving on a beautiful coral reef. The ridges reach upward from white sandy bottoms in a colorful display of tropical marine life unequaled anywhere. Then, as you glide over the next coral ridge, you are confronted with the rusted hull of an old car body. It seems thoughtless to desecrate such natural beauty, even if there are several large grouper and snapper hiding in the old car’s trunk and engine area. You ask the question – who needs artificial reefs in an area where natural coral reefs abound? The answer, surprisingly, is that the fish and the coral now need such reefs if they are to survive the ever-increasing pressure of divers and fishermen.
Using artificial reefs to attract food and game fish to areas easily accessible to fishermen is not a new idea. Divers have long known that a wreck is an excellent place to find large populations of not only food and game fish but also colorful tropical species. Sport fishermen in the United States began building artificial reefs of old car bodies in the 1950s, but commercial fishermen in Japan were even then developing prefabricated concrete structures to serve as fish habitats. At first, these reefs were thought to be simply a means of concentrating existing fish populations into an area easily accessible to fishermen. Then, in 1966, the author completed a master’s thesis that indicated these reefs, when built within the sunlit photic zone, can actually increase the basic food production of the sea by providing suitable substrate for benthic algae (benthic means bottom dwelling). This increase in basic food production then supports a larger fish and invertebrate population. Published scientific studies by the author and others have shown that artificial reefs, when sited and built correctly, can actually support a larger total fish population than a natural reef, even a tropical coral reef. To many a biologist that statement is close to blasphemy. To think that anything manmade could improve upon a natural community is almost unthinkable. But this is actually an established fact and the reasons are not so complicated when you stop and think about it. A coral reef grows in such a manner as to maximize coral survival; fish that live on the reef are incidental to the coral’s growth patterns. With an artificial reef, the fishery biologist is deliberately shaping the substrate so as to maximize fish habitat. We have even learned to design different types of artificial reefs for different types of fish. If we want large populations of benthic fish species, like grouper and snapper, we build a reef with a medium profile and lots of open spaces up under the material. If we wish to attract pelagic species, like mackerel, amberjack and barracuda, then we build a reef with a high profile but lots of open space within the upper structures.
Any experienced diver knows what it is like to swim over an open sand or mud bottom, a barren desert with only a few sand dollars or sand perch to break the monotony. But once you find some relief on the bottom, it becomes an oasis of marine life. The name “artificial reef’ is maybe misleading at first, because the only thing artificial is the original substrate. All the marine communities that grow in the reef and are attracted to it are natural and are the same basic species that populate natural reefs in that area. Any hard surface will provide attachment for these benthic communities, but materials that do not deteriorate in sea water such as concrete, fiberglass and synthetic rubber, provide the most durable types of reefs. Unfortunately, a few artificial reefs in the past have been built in areas where wave action was able to dislodge the materials or the bottom was too soft, so the reef lost much of its effectiveness after a few years. If built correctly in an appropriate site, however, an artificial reef will continue to provide fish with a habitat for literally thousands of years. How many things can we build today that we can be sure are going to be beneficial to nature 2000 years in the future?
Okay, so you agree artificial reefs may be useful along coastlines that are devoid of natural reefs, but why build them in tropical waters where coral reefs grow? Tropical waters of the Florida Keys and the islands of the Caribbean abound with natural coral reefs, so they need no help from man, right? Wrong! To begin with, the fringing types of coral reefs that occur in these waters are by no means complete in their coverage of the seafloor. The normal occurrence may be a three to five acre reef surrounded by several miles of open sand bottom. Often these reef patches may be some distance from marinas or boat ramps, requiring long boat runs burning expensive fuel to reach the dive spot. So, why not build an artificial reef closer to the marina for diving on those days when the weather is not optimal or when those end-of-the-month cash shortages require shorter runs? Recent innovations in reef-building technology, developed mainly in Japan, have produced very effective reefs that can be built without heavy equipment and large barges. These reefs can help the diver or the fisherman, but how can they actually help the coral reef? You would never place an artificial reef on top of or even adjacent to a natural coral reef. This would increase the fish population but at the expense of what is already present. Rather the artificial reef should be at least one-half mile, preferably farther, from the natural reef. Any coral reef receiving heavy diving and fishing pressure is going to begin to show signs of stress. Anchors will break coral and heavy fishing will begin to deplete the population of larger predatory fish. Nearby artificial reefs can take much of this pressure off natural reefs, thereby allowing the natural reefs to replenish themselves. The beautiful thing about artificial reefs is that there is literally no saturation point on their construction. If we double the available fish habitat, we can double the fish population, double it again, and again double the fish. The reason for this is that most marine fish can produce literally millions of eggs, but only those few that find suitable habitat and food will grow to maturity. So, increase the substrate and you will increase a proportional amount of the fish population. The early artificial reefs in this country were built from old car bodies and even some old wooden trolley cars. These initially attracted large populations, but in a few years they deteriorated. One theory was that the marine life covering the car bodies would remain after the metal rusted away, but this is not the case, so thin metal structures such as car bodies are no longer used. Old tires are almost impervious to deterioration in sea water and are readily available in most coastal areas. However, the tires must be vented or split to allow the entrapped air to escape and must also be ballasted with concrete to be stable in the water at depths less than 100 feet. Some tire reefs that were not well ballasted have shifted off their original site; a few even washed up on adjacent beaches after a storm. It only takes a few foulups like this to hurt reef building throughout the country. The technology and expertise to properly select a reef site and the proper materials suited for each area are readily available from universities and fish and game agencies in most parts of the country today. Recent improvements in Loran C have now made it possible to actually build a small artificial reef for one’s own private use.
So, the next time your dive club is searching for a worthwhile activity, why not consider building an artificial reef, either alone or in conjunction with local angling organizations? Such cooperative projects have occurred around Florida, and not only improved fishing and diving, but improved relations between fishermen and divers. Additional information on artificial reef site selection, materials and construction, and artificial reef buoys can be obtained by writing Florida Sea Grant in Gainesville, Florida.