Artificial Reefs

Artificial reefs

BY E. Romano & C. Provenzani

Photo by Claudio Provenzani


The popular conception of a “reef,” generally refers to a coral barrier found in a tropical marine environment. Here people imagine a wide variety of tropical species swimming within a labyrinth of hard corals, gorgonians, and sponges in search of shelter, prey or a place to graze.

Such a habitat is typical in tropical regions located near the equator, between the Tropic of Cancer and the Tropic of Capricorn. Here temperatures consistently range between 21° and 22° C and climatic conditions prove uniform throughout the year.

In contrast, areas with more temperate climates, such as the Mediterranean Sea, are unsuitable for most reef organisms. In such areas, “reefs” are replaced by “rocky bottom areas” characterized by a wide variety of benthic organisms, such as calcareous and encrusting algae, corals, vermetids, bryozoans, sponges, bivalves and polychaetes.

Both sets of conditions, tropical or temperate, produce fragile and complex ecosystems whose extent and distribution proves to be quite limited when compared to the total length of available coastline. This fact makes particularly disturbing the realization that, as attractive environments, they are subject to heavy, sometimes destructive, stress loads from the tourist and scuba diving industries. This results in the need for human intervention, in the need to find ways to protect these delicate ecosystems. One solution to this problem is to create new reef habitats, or “artificial reefs.”


Artificial substrates are colonized by benthic invertebrates and fishes.


Artificial reefs are created when human-made objects are introduced into a marine ecosystem in such a way that they become an integral part of it. In the last few years, this practice has become more commonplace globally, with the principal aim being to encourage the founding of new, fragile, marine ecosystems.

However, sometimes (even often), these barriers are unplanned, the result of a vessel going down at sea. In such cases, the environmental damage caused by the sinking greatly outweighs any short-term benefit it offers.

In contrast, when an artificial reef is not accidental, but planned, materials suitable for extended submersion in a marine environment are normally used. Such materials are stable and environmentally sound, like, for example, cement or steel.

Once the material is introduced into the marine environment, it acts as a natural rocky bottom, providing potential living space for a new reef community. Furnishing this “suitable space” is the only human intervention needed; once in place, nature quickly takes over and, soon thereafter, the structure begins to lose its artificial character. With each passing day, as numerous new living organisms begin to colonize the structure, what was once “artificial” now becomes a progressively intensifying reef ecosystem. In time, the steel and cement will disappear beneath a colorful blanket of undersea life.

Over the last few years, decommissioned vessels and oil platforms have progressively replaced the use of specialized materials as building blocks for artificial reefs. This is especially true of areas where scuba diving is very popular or of areas where there is a lack of a suitable substrate to support the organisms that make up a reef ecosystem.

A good example of a well-designed, well-planned, and well-executed artificial reef can be found in the National Marine Park of Isla Mujeres in Mexico. This national park was established in 1996 in the Caribbean marine area delimited by Cancun, Isla Mujeres and Puerto Morelos in the southern state of Quintana Roo.

The reef (so far) consists of two decommissioned minesweepers, gifted to the park by the Secreteria de Marina Armada de Mexico (SM-AM). These are the C-58 Anaya and C-55 Juan de la Barrera. The vessels, each 60 feet long and of 1,000-ton displacement, were sunk at a depth of 83 feet/25 meters on May 28 and October 25, 2000, respectively.

The park management decided to use the “artificial reef strategy” to try and protect its coralline barrier because of the important ecological and tourist value it offers. Future plans by the park’s monitoring project include the sinking of several additional structures to provide further building blocks for new marine ecosystems. These will be strategically placed around the marine park area to create alternative diving sites for the burgeoning scuba industry and to reduce the environmental impact caused by scuba diving activities on natural marine ecosystems.

The success, or rather, the outcome of an “artificial reef” is always bound to several environmental factors, such as the geographical location of the chosen site, its depth, its real distance from a natural reef, the trophic status of the water column, and the morphological and sedimentological characteristics of the sea bottom.

What follows is an examination of various activities and stages involved in planning and creating an artificial reef.


Evaluation of the Environmental Impact on the Chosen Site

Carrying out an environmental study of the target area is the first step in an artificial reef project.

All the important parameters that impact the existence and distribution of reef organisms must be taken into account. A precise knowledge of the hydrodynamic characteristics of the area, such as the direction and intensity of the currents and the amplitude of tides, is extremely important in determining what the correct position and orientation of the wreck should be.

Other important factors to consider are the rate and nature of the sediments (generally sandy or muddy). This is important because sediments may be altered by the presence of the wreck, with the result that a new sedimentation pattern could muddy the wreck and render its position useless. Human impact and its potential use of the new site must also be assessed.

The wrecks’ impact on the marine habitat must also be considered, for example, on established biological communities and their existent trophic relationships. Particular attention here must also be given to both endemic organisms and threatened or endangered species.

It is therefore necessary to concurrently launch a monitoring program that will allow us to: a) evaluate the reaction of the environment to the placement of the wreck and b) the time required for the “artificial reef” to reach a state of environmental balance.

Clean Up the Wreck

Wrecks are “cleaned” with two main aims in mind: to make them “environmentally safe” and “diver safe.” Wrecks can pose a threat not only to the environment but also to divers. To minimize these threats, wrecks must be checked, and to the degree that this is possible, these risks must be eliminated.

To make a wreck “environmentally safe,” all potentially toxic substances must be removed from a vessel before it is sunk. These would include hydrocarbon residues, especially those still in a ship’s fuel tanks, heavy metals, PCB (Polychlorobiphenyls) from any refrigeration equipment, and any anti-vegetative paints which by design pose a threat to marine life.

To make the wreck “diver safe,” all objects and structures that could prove dangerous during a recreational dive have to be removed or modified. Metal wires are removed, access to confined areas is denied, all portholes are either removed or sealed, and wide openings are cut in the structure to allow for a constant view of the outside of the wreck.


Positioning the Artificial Reef

The final step requires placing the wreck at the target site, in an orientation and position that has been previously agreed to as the best one possible.

The scuttling of the ship is generally supervised by a government environmental protection agency and carried out by specialized firms who use explosives to sink the wreck in a pre-selected position with a minimum of impact on the local environment. Once it reaches the bottom the wreck is hooked with a buoy to mark its location and to facilitate surface identification.

Monitoring Program

Now, as the new environment begins its journey towards stability, the only thing left for human beings to do is wait, and watch. Observation will yield an account of the various benthic organisms settling into their new habitat, of which fish species will be the first to move in, and of the interactions that occur between the different organisms. The best way to observe this sequence of events is to dive the new site at regular intervals, and to record existing changes to organisms, either invertebrate or fish, in or around the wreck.

We dived the Anaya only two months after she was sunk. The wreck is positioned near Cancun beach at a depth of 83 feet/25 meters, in navigation side, and in moderate current.

We knew that after only two months, the wreck would not be completely covered byhard and soft corals, filtering organisms, sponges or other invertebrates. What we were interested in seeing was a newly sunken wreck in the early stages of its underwater life; we wanted to see the first colonizers... Only dark seaweed covered the vessel’s structures; other benthic organisms had not yet had time to settle. However, a number of fish species had already begun the colonization process. Barracuda, generally the first species to colonize and to define their territory, were present, as were large schools of different kinds of “snapper,” e.g., gray and yellowtail. These fish are typical of tropical areas, and are characterized by obvious schooling behavior. We also observed grunts, surgeonfish, damselfish, jacks, grouper, wrasse, bluehead, goby, and parrotfish and, in the wreck fissures, many very small lobsters and morays.

It’s enchanting to see a military vessel, which served in the Navy for more than fifty years, become the promising foundation for a new, vital, marine ecosystem.

Projects like these represent important enterprises, regardless of whether they are intended for scientific or recreational ends. Apart from whether an artificial reef program serves scientific interests of acquiring information on marine ecosystem colonization, or whether it serves economic or recreational interests geared towards open water divers, by enabling divers to observe a beautiful coral reef without stressing a fragile and irreplaceable habitat, it provides everyone concerned—human and nonhuman—with an invaluable service.

Acknowledgements:

• Ing. Francisco Ursua Guerrero (Director of Cancun Park) and Dr. C. Miguel Angel Garcia (Investigation and Monitoring Project Chief) for providing us with a great deal of information on the Managing Park Project and with the photos of the sinking of the C-58 Anaya
• Marcella Pesce and Nick Connell for translation assistance


Some information on National Marine Park of Isla Mujeres – Cancun, Mexico:

This area is the result of intense citizen cooperation and of the awareness of a need to protect the coralline habitat of Quintana Roo. Actually, it represents the first protected area auto-financed in Mexico by the increase in tourism.

The Director is Dr. Francisco Ursua Guerrero, while Dr. C. Miguel Angel Garcia serves as Investigation and Monitoring Project Chief. Some of the park’s main purposes include:

• To contribute to the conservation of the Caribbean reef ecosystem
• To contribute to the stability of ecological processes, marine productivity and biological stability in the reef system
• To promote environmental education
• To promote scientific research in natural resources management



Another view of the reef at the Narional Marine Park
of Isla Mujeres, Cancun, Mexico

 

Copyright ©2002 Global Underwater Explorers.
All rights reserved.

 
A typical reef inhabitant
The wheel house of C-58 Anaya 
The wreck of C-58 Anaya
sunk in front of Cancun beach
to create an artificial reef in Cancun Marine Park
C-58 Anaya

Anemone at National Marine Park of Isla Mujeres 
Cancun, Mexico