Articles

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.

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 e