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Mauritius Marine Management Notes
Thomas J. Goreau, Ph.D. Summary Mauritius coral reefs are generally in poor condition and in urgent need of restoration. The reefs mostly have low abundance of live corals even though Mauritius was fortunate to be only mildly affected by the deadly heat wave that killed most of the corals in the Indian Ocean in 1998. The major causes appear to be land based sources of sediments and nutrients. Inspection of coral reefs on the east, west, north, and south of the island indicated a serious problem with algae overgrowth, which appears to be quite recent in most sites. This is likely due to excessive nutrient inputs from sewage and agricultural fertilizers. The result of reef deterioration is decreasing tourism, fisheries, and shore protection values, and increased beach erosion. Large-scale coral reef restoration and shore protection efforts are needed. A pilot coral reef restoration project was initiated, and partners for such projects identified in the Mauritian governmental, non-governmental, and private sectors. A strategy for coral reef, beach, and fisheries restoration in Mauritius is outlined. A project to develop renewable energy supplies from tidal currents in Mauritius is also outlined. GCRA is ready to assist Mauritian organizations to actualize such strategies. Introduction An extremely well developed coral reef, surrounding almost the entire island, and growing almost up to mean sea level, shows that Mauritius formerly had almost ideal conditions for reef growth. The inshore fisheries and white sand beaches are the direct products of this reef. However a steady decline in live coral cover has been noted by divers and by the monitoring programs of the Ministry of Fisheries over many years. Most coral reefs now have far more dead coral rubble than living corals. As the result, the reef barrier that protects the shore is being broken down by physical and biological damage faster than it can grow, resulting in increased wave energy at the shoreline, followed by increased beach erosion at many sites. Tourism is now set to become an even more important part of the Mauritian economy as textile and sugar preferences disappear this year, but without reef restoration there may be little beach, fish, or corals to attract tourists. The major stress factors to Mauritius lagoon reefs are likely to be land-based sources of sediments from erosion of agricultural land and deforested slopes, and nutrients from sewage and fertilizers. Historically the damage from erosion should have been greatest just after the sugar industry expanded to most of the low land a couple of hundred years ago. Fertilizer runoff should have increased greatly as chemical fertilizers became more widely applied, and then declined recently as the result of more efficient use. However sewage nutrient runoff should have greatly increased along with population growth. Damage to Mauritian reefs also includes global warming, leading to coral bleaching, but so far Mauritius has been lucky. The devastating heat wave that killed most of the corals in the Indian Ocean in 1998 had only a minor effect on Mauritius (Goreau et al., 2000). However such hot conditions are likely to return as global warming intensifies (Goreau & Hayes, in press). Reef Assessment Quick assessments of coral reef health were done in lagoon reefs on the east (Ile aux Aigrettes), west (Flic en Flac), north (Grand Baie), and south (Bel Ombre) of Mauritius in January 2005. These observations were discussed with local divers from the Marine Conservation Management Consortium (Ian Watt, Aurelian Nahaboo), the Mauritius Institute of Oceanography (Ruby Moothien Pillay, Dr.Mitrasen Bikhajee, Coralie Charles), environmental consultant Rajiv Bheroo (Mauritius' first marine biologist and former head of the Ministry of Fisheries Coral Reef Monitoring Program), the Mauritian Wildlife Federation (Francois de Maroussem, Pierre de Boucherville Baissac), and representatives of fishing communities (Julien Lourdes of the Mauritius Council of Social Service and others). 1) Ile aux Aigrettes Live coral cover on the submerged rocky shores of Ile Aigrette was low, under 5%, but composed of healthy young corals of diverse species. The rocky hard bottom was clean of weedy algae, and was suitable for young coral settlement. The lack of older corals indicate that there had been high mortality about 5-10 years ago, and the relatively small number of young corals indicates that although conditions are now good for coral growth, there is a limited supply of juvenile coral larvae settling. In contrast to the clean rocks at Ile aux Aigretttes, rocks along the shore of the main island had high abundance of green algae species indicating high levels of nutrients. These could be derived from coastal development, the nearby mangroves, or Mahebourg. 2) Flic en Flac Live coral cover was generally low, under 5%, but both live coral and coral diversity increased from the shore towards the outer edge of the reef flat, being highest next to the tidal channel. Most of the bottom was made up by dead coral rubble and sand patches. Near shore the predominant coral was a staghorn Acropora, forming patchy thickets. These were largely made up of a single clone that has spread by fragmentation. Near the underwater spring these corals were being overgrown by green algae, whose spatial distribution suggests they are being fertilized by nutrients from the spring. Large areas of dead coral, coral rubble, and sand were covered by slimy mats of cyanobacteria of at least three kinds. The cyanobacteria are an indicator of excess phosphorus pollution. Local residents long familiar with the site said that these cyanobacterial mats had not been there in the past, had started to spread fairly recently, and that they had never been so bad. This strongly suggests that the area has only recently become overloaded with nutrients as the result of coastal development. The cyanobacterial mats on dead coral rock prevent settlement of juvenile corals and retard ecosystem recovery. This in turn is contributing to the erosion of the beaches, as seen by the Casuarina and other trees whose roots are eroded, and the construction of seawalls and groynes, which are failing since they only concentrate wave scour and erosion at their bases. The erosion problem at Flic en Flac has long been recognized, and a plan has been approved to start shore protection measures to save the beach (R. Bheroo, pers. comm.) 3) Grand Baie Reef areas examined had very low live hard coral cover, under 1%. The bottom was made up of dead coral rubble, overgrown by algae, and an encrusting soft coral. The algae appeared to be inhibiting any settlement of juvenile coral larvae. 4) Bel Ombre The Bel Ombre reefs had areas of nearly 100% live coral cover, dominated by huge colonies of Porites, Montipora, and many other genera. Many of these colonies were very old and healthy, indicating that growth conditions for coral had been excellent at this site for many centuries. The species diversity was also very high, including many corals that had not been previously seen in the Maldives or Seychelles. However all dead corals were overgrown with dense mats of algae and cyanobacteria, and little new coral settlement seemed to be possible. At least three species of cyanobacteria formed large slimy mats on live coral, dead corals, and sand, or had detached from the bottom and had floated to the surface. Ian Wat, who had surveyed the reefs a few years ago prior the recent hotel developments in this area, had not seen any of these cyanobacterial mats, indicating that they were very recent and had followed development of the coast. Local divers reported that there were "bleaching white corals" on this reef. All patches of white corals were found not to be due to bleaching or coral disease, but to have been recently eater by the poisonous Crown of Thorns Starfish (COTS). Two large COTS were removed from the reef. Patches of dead coral overgrown with algae appear to be the results of a COTS infestation. This was an exceptionally rich and healthy reef that has only recently been badly damaged by algae and cyanobacteria from very recent nutrient inputs to the coastal waters. Because of their great importance for ecotourism, biodiversity, fisheries, and shore protection the sources of excess nutrients urgently needs to be identified and cleaned up. Since sugar cane cultivation on the hill slopes above is not new, it is likely that the source of the nutrients is from land alteration during development, and most likely from leakage of nutrients from the septic systems of new hotel developments. Waste water discharges following secondary sewage treatment contain virtually all of the nutrients, and should not be allowed to drain into the sea, as it causes severe algae overgrowth and eutrophication of coral reefs and fisheries (Goreau, 2003). These effluents should be used for watering lawns and ornamental gardens, or golf courses, absorbing the nutrients on land, eliminating pollution of the reefs, and the need to buy chemical fertilizers for the plants (Goreau, 2003). Reef Restoration: Pilot Project All sites seen were in clear need of active restoration projects to increase coral and fish populations, coupled to identification and reduction of land based sources of nutrients. A pilot coral nursery project using the Biorock™ method is proposed for a site near Grand Baie. The Biorock™ method of Hilbertz and Goreau uses safe low voltage currents from solar panels, batteries, windmills, tidal turbines, or chargers to grow solid limestone structures of any size and shape in the sea. It is now being used to restore marine habitats in over 15 countries. Biorock™ structures greatly increase coral growth rates (3-5 times), coral healing from breakage (over 20 times faster), coral survival from high temperatures, sediments, or algae overgrowth (16-50 times higher survival in the Maldives in 1998), coral settlement (hundreds of times), and fish and shell fish populations. By growing Biorock™ reefs in front of a severely eroding beach in the Maldives, the beach grew 50 feet in a few years (Goreau, Hilbertz, and Azeez Hakeem, 2004). Besides protecting the shore, Biorock™ reefs are tremendous ecotourism attractions. They have been awarded the Sperry Award for Pioneers and Innovators from the Society for Ecological restoration, the Maldives Environment Award, the SKAL Award for best underwater ecotourism project n the world, the KONAS Award for best community based coastal zone management project in Indonesia, Indonesia's top environment prize, the Association of South East Asian Nations Tourism Association top environment prize, and the Pacific Asia Travel Association Gold Award for best ecotourism project. In addition, because of the dense populations of fish that these projects build up, Biorock™ reefs are a major tool for restoring reef fish stocks and allowing their sustainable management at higher yields. A small pilot project, a few meters long, is proposed for a site outside Grand Baie where there is almost no live hard coral left, and where power is available on site from a solar powered raft used for tourism. As this site is lacking in coral and fish for the divers, and is protected, it is an ideal site for a small pilot experiment to compare the growth of corals and fish populations on a small charged structure in comparison with nearby coral rubble. It is proposed to start the project at the end of the Cyclone Season. The proposed structure is made up of rolled up fencing material supported with steel bars. The Biorock™ process will stop all rusting, and will in fact reverse it. Within a few days the structure will turn white as limestone rock starts to grow on it, becoming stronger and thicker with age. Broken coral fragments attached to it will proceed to grow very rapidly, and abundant fish populations, especially juveniles will be attracted to live there. Reef, Fisheries, and Beach Restoration: Long-term Strategy Mauritius, like every other SIDS, has been locked into a strategy of "monitoring" the demise of its reefs, which has failed to stem the decline. A new strategy based on active restoration is needed if its tourism, fisheries, biodiversity, and shore protection resources are to be sustainably managed. Mauritius has the human resources in the governmental (MOI), non-governmental (MCMC, fishermen's associations), and private sector to actively restore the reefs. We suggest that a strategy could be built as follows: 1) Set up and monitor pilot coral restoration projects. MCMC, in conjunction with a local dive operator, is ready to start a small pilot project in an area of badly damaged reef near Grand Baie. MCMC and MOI would be able to document the results in terms of coral growth and fish populations in comparison with nearby control areas. 2) The 4th Western Indian Ocean Marine Science Association (WIOMSA) Scientific Symposium will be held in Grand Baie August 23 - Sept 3 2005. A hands-on training course in coral reef restoration and shore protection should be held after the symposium. The course would be taught by Prof Wolf Hilbertz and Dr Tom Goreau, the inventors of Biorock™ Technology. Participants would include divers, government agencies, NGOs, community groups, and tourism interests in Mauritius, as well as interested groups from Seychelles (where a Biorock™ project is already underway there with government and NGO participation), the Comoros (at least three groups are interested), Madagascar (where a project is being developed), and East Africa. The President of WIOMSA, Dr, Nyawira Muthiga, has indicated that such a workshop could be funded by WIOMSA if MOI and MCMC were to sponsor it and if all member states of WIOMSA could benefit. But the applications would need to go in soon for this to happen (the deadline is in the first week of March). The hands on training course would visit the existing pilot project, and construct a new one at a site to be chosen, preferably near the first one. 3) A shore protection plan to reduce erosion of the beach at Flic en Flac has been approved to start in the next year. This plan proposes the use of concrete "artificial reef" breakwaters. Since Biorock™ reefs would be far cheaper and much more effective, we propose to work with Rajiv Bheroo to incorporate Biorock™ reefs into the initial phases of this program, and to expand these projects if the initial results warrant it. 4) A national program of coral reef restoration for ecotourism, shore protection, and fisheries restoration needs to be devised. Hotels, most of which have little in front of them to show snorkellers. Could grow reefs in from of their beaches that would provide safe nearby habitat full of corals and fish for their guests, and that help replenish lagoon fish populations, while protecting the beaches from erosion. Fishermen could also be growing coral reef habitat to increase the populations of fish, shellfish, and octopus for sustainable harvesting. MCMC could be the lead organization in implementing these projects. 5) A detailed study of the distribution of algae in Mauritius reefs should be made by MOI in order to identify all the sources of nutrients causing algae overgrowth of the reefs. Identification of sources should be followed by projects to recycle these nutrients on land to eliminate pollution of the coastal zone, and increase productivity on land. Tidal Energy Development Although Mauritius is a pioneer among SIDS in effort to develop renewable energy resources, its tidal energy resources remain untapped. Strong tidal currents flowing through the main passes and channels could be used to make electricity by means of Gorlov vertical axis helical turbines. A turbine about 2 meters in size makes a kilowatt of energy in a 2 m/sec current, and the power output goes up as the cube of the velocity. Several locations in Mauritius, in particular near Mahebourg, could be ideal for tidal energy production. We propose that a pilot project be set up with Dr. Alexander Gorlov (inventor of the turbine), GCK technologies (manufacturer of the turbines), and MOI to see if this is a practical and cost effective energy source in Mauritius. If it is shown to be, a study should then be made of the current velocities at all prospective sites in Mauritius and Rodrigues to determine the potential magnitude of the resource and the best sites to develop. Fabrice Madre, a Mauritian student interested in working on this technology, could start such studies with MOI. Acknowledgments I thank Ian Watt, Aurelian Nahaboo, and Veerle Van Roy of the Marine Conservation Management Consortium, Dr. Mitrasen Bikhajee, Ruby Moothien Pillay, Coralie Charles, and the staff of the Mauritius Oceanography Institute, Rajiv Bheroo, Pierre de Bouchervile Baissac and Franxcois de Maroussem of the Mauritian Wildlife Federation, Julien Lourdes of the Mauritius Council of Scoial Service, and Mauritius fishermen for information and discussions. The Global Coral Reef Alliance is ready to work with all these groups to help develop and apply new technology for the sustainable management of Mauritius' marine resources.
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