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Artificial Reef Project
of The Western Isla Mujeres, Preliminary Results
Thomas J. Goreau, Gerardo Garcia, Miguel Angel Garcia,
January 9 2001
INTRODUCTION Coral reefs are the richest and most beautiful marine environment, containing a great diversity of animal and plant species. These characteristics have made them very popular sites for the development of aquatic activities. Isla Mujeres used to be bordered by a well developed fringing reef dominated by Acropora palmata (Elkhorn) and Acropora cervicornis, (staghorn) as shown in the photographs of Ramon Bravo, but these species have almost completely disappeared, and one sees only a few standing alone in some isolated locations along the shore, such as La Cadenita reef, where the strong currents make it impossible for swimmers to visit.
The causes of this decline include contamination, removal of corals for sale, damage by visitors, hurricanes, and diseases, among other factors. Because of this the Marine Park has developed an Artificial Reef Program with the goal of restoring the damaged areas and offering alternative sites for aquatic recreation.
PREVIOUS WORK
As part of the Research and Monitoring Program of the Western Coast of Isla Mujeres, Cancun Point, and Nizuc Point National Marine Park, an Artificial Reef Project was established using the Mineral Accretion method of Wolf Hilbertz and Thomas Goreau.
This method is unique, differing from others in the capability of making growing structures of limestone rock of practically any shape and size which increase the growth of corals, promoting the development of a true reef ecosystem. The Mineral Accretion method also is very economical in terms of cost of material required.
n August 1999 the first structure was placed in the reef of Sac Bajo, next to Isla Mujeres, with the shape of a triangular prism of size approximately 3 meters long and 1.5 meters high.
In March 2000 a second structure was placed at the same location, approximately 5 meters away from the first. This structure was named "El Doble Caracol" (twin snail shell), owing to its shape of a double spiral of steel construction mat, approximately 4 meters long, 3 meters wide, and 1.5 meters high.
Both structures are fed with electrical current from solar panels located on the shore which are connected to them by cables. Direct current is used, with a voltage less than 6 volts, which makes the structures completely safe for human beings and also for marine life.
Coral fragments were transplanted onto these structures from the area of La Cadenita reef damaged by the boat accident that took place there the previous year. Species transplanted were Acropora palmata, Acropora cervicornis, Acropora prolifera, Porites porites, Porites furcata, Agaricia agaricites, Siderastrea siderea, Diploria strigosa, and Dichocoenia stokesii.
RESULTS
Up till now one can see Mineral Accretion of limestone rock up to 2 centimeters thick on some parts of the Prism; the Doble Caracol has a larger surface area for deposition, and the growth is slower.
The transplanted corals have strongly cemented themselves to the structure. The state of health of the corals is good, shown by their rapid growth, dense branching, bright color, and extended polyps.
In addition, one observes that soft corals have cemented themselves to the walls of the structure. These were not artificially transplanted, but have cemented themselves naturally.
Immediately after they were placed, the structures showed dense populations of fishes, especially Grunts. These fish form dense schools, through which it is practically impossible to see the other side of the structure. Other fish species observed were Groupers, Snappers, Butterflyfish, Angelfish, Damselfish, Parrotfish, Wrasses, and other species. In addition lobsters and cleaning shrimp are observed.
The growth of algae is also observed, primarily on portions where the Mineral Accretion is growing more slowly. These growths do not appear to damage the corals, and they can be controlled by increasing the electrical current. At times the growth seems to be temporary, occurring occasionally during the year.
Coral mortality is relatively low, only two dead colonies have been seen attached to the structure, and a few broken fragments nearby.
Two types of damage are seen to the transplanted corals: physical damage caused by waves or visitors (several hundred swimmers may pass over the shallow structures every day); and biological damage caused by Fire Worms (Hermodice carunculata) which eats the tissue of Acropora cervicornis and Acropora prolifera, and Parrotfish bites, which damages the tips of Porites porites.
These structures have become an important tourist attraction due to their location along the snorkel trail used by local operators. The artificial reefs provide a location with unique characteristics, different from that observed at other locations due to its population of branching corals.
RECOMMENDATIONS
Based on the results observed during the field trips, we establish some recommendations that will serve to make the project more effective:
A much larger number of coral fragments should be transplanted onto both structures until they are completely covered with corals.
The largest number of coral species as possible should be transplanted, with the goal of increasing the biodiversity of the site.
The electrical current should be increased, principally on the Doble Caracol, where the accretion is slower. Increasing the electrical current will increase the rate of growth of the corals and reduce the algae.
More anodes should be placed in order to obtain more uniform Mineral Accretion growth.
A regular program of monitoring should be implemented to record the progress of coral growth and the rate of accretion.
Information should be provided to the tour operators and tourist guides, in order to make them aware of the objectives of the program and its importance.
Visitors to the artificial reef should be informed about its importance, benefits, and the care that they need to take, such as not touching the structure or the corals. This information could be spread through posters in the dive shops and hotels.
The structures need an adequate program of maintenance to repair any physical damage to cables and anodes caused by waves and visitors. Damage to corals should be noted and broken fragments re-attached.
Tour operators could collaborate in the monitoring of the artificial reefs.
It is recommended to expand the structures along the length of the coast of Sac Bajo and other locations, to create a large artificial reef for ecotourism, and at the same time promote the restoration of the natural coral reefs.
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