Mauritius island is just a small volcanic dot in the Indian ocean, yet its legal coastal waters are more than 1000 times its terrestrial size. Basically, the island has a land area of 2,040 km2 and an Exclusive Economic Zone of 2.3 million km2 (including 400,000 km2 jointly managed with Seychelles). This is because the territory of Mauritius extends over its dependencies, namely Rodrigues, Saint Brandon (or the Cargados Carajos Shoals), Agalega, Tromelin and the Chagos Archipelago and cover their coastal waters as well. Though the marine zone is quite rich, 99% is still unexplored. Howbeit, the coastal and marine biodiversity has been well studied revealing several important species in the Mauritian waters.
Coastal biodiversity refers to the plants and animals that are found in the coastal zone. The coastal zone here represents the interface between the land and sea and includes several sub-zones such as river estuaries, wetlands, beaches, islands, intertidal regions and salt marshes. The most important marine ecosystems on Mauritius are the mangroves, seagrass beds and coral reefs.
Wetlands that appear on the coastal zone are mangrove forests, estuaries, marine coasts and marshes. Among these, mangroves are the most important element covering an area of 0.49 km2. Basically, two species of mangroves grow on the coast: the red mangrove (Rhizophora mucronata) and the black mangrove (Bruguiera gymnorhiza). The red mangrove is the dominant species and can be easily recognized by its stilt roots. Also, plants that grow in the wetlands are mainly the golden leather fern (Acrostichum aureum) and the common bulrush/cattail (Typha latifolia). To date, there has been no inventory on the animal species that inhabit the mangroves of Mauritius. Broadly speaking, commonly encountered creatures are juvenile fish, crabs, birds, stray cats and a plethora of insects.
Seagrasses are flowering plants that have adapted to live underwater and are different from algae. They often form extensive meadows and have important ecological functions especially in terms of their blue carbon potential. Basically, 13 species of seagrasses have been identified in the Western Indian Ocean. But there is a lack of knowledge on their species composition and density around Mauritius. Some of the species identified include the Narrowleaf seagrass (Halodule uninervis), the Halophila seagrass (Halophila stipulacea), the Spoon grass (Halophila ovalis) and the Noodle seagrass (Syringodium isoetifolium).
Five types of coral reefs are found around Mauritius namely fringing reefs, atolls, patch reefs, reef flats and barrier reefs. Moreover, more than 160 species of corals have been identified. As it is, coral reefs form a 150 km protective layer around Mauritius with a few gaps at river mouths and in the south. They are also ecologically and economically important; for instance, by breaking open sea waves, they permit a calm lagoon to form which is crucial for the tourism industry. Nevertheless, the crown of thorn starfish frequently preys on corals thus preventing their regeneration.
In general, 1656 marine species have been recorded from the waters of Mauritius. This includes several species of crabs (4), shrimps (7), lobsters (2), bristle worms (polychaetes), bivalves (e.g. mussels, oysters, clams), isopods, octopus, molluscs and sea cucumbers.
In general, there are 340 fish species; out of this, 42 species within the lagoon are economically important. Some fish species endemic to Mauritius are the Mauritius dragonet (Callionymus mascarenus), Smith’s Dottyback (Chlidichthys smithae) and the moray eel (Gymnothorax sagenodeta). Moreover, deep-sea fishing is also an important recreational and economic activity for big game enthusiasts. Common species outside the lagoon of Mauritius are the Pacific Blue Marlin, the Sailfish, the Dorado and the Yellow Fin Tuna.
To date, some 17 marine mammal species have been documented in the water around Mauritius. This includes dolphins, whales, sea lions, dugongs and seals. For the most part, these beautiful creatures can be sighted when they migrate from the colder Antarctica waters to the warmer tropical waters for calving. Amongst these, dolphins are the most common species that can be viewed on the west of Mauritius. Whales, sea lions and seals make an appearance every now and then, but dugongs are now rarely seen due to predation and hunting pressure.
2 species of marine turtles are encountered in the Mauritian waters: the hawksbill turtle (Eretmochelys imbricate) and the green turtle (Chelonia mydas). While they feed in the seagrass beds around Mauritius, Saint Brandon and Agalega, they nest only on Saint Brandon and Agalega. Both of these turtles have been exploited in the past for meat, eggs and leather; so, today, they are protected under the Fisheries and Marine Resources Act.
There is very little information on the marine birds of Mauritius. As it stands, marine birds are monitored mainly at the Rivulet Terre Rouge Estuary Bird Sanctuary (RTREBS) and on the offshore islets around Mauritius and Rodrigues. At the RTREBS some 1200 bird species migrate from the northern hemisphere during the harsh winters to the warm climate of Mauritius. Common migrant birds are the common Sandpiper, the Little Ringed Plover and the Grey Plover. Above all, the offshore islets Gunners Quoin, Round Island and Flat Island shelter most of the marine bird species. Thus, white-tailed tropicbirds, red-tailed tropicbirds, Bulwer’s Petrel, the Round Island Petrel and the Wedge-tailed shearwater can often be glimpsed flying over these islands. On the islets of Rodrigues as well several bird species are closely monitored such as the Lesser Noddy, the Sooty Tern, the Fairy Tern and the Roseate Tern.
As a rapidly developing small island state, the main threats to coastal and marine biodiversity are related to development activities. Many wetlands have been filled for construction purposes and mangroves have been cleared for the same reason. In addition to that, hard structures on beaches coupled with unsustainable development has increased erosion rates in many regions. Invariably, land-based and coastal activities lead to pollution that degrade the coastal environment considerably. High levels of chemicals encourage eutrophication thus choking plants and animals under algal blooms. Moreover, certain invasive alien species such as the Crown of thorn starfish impact on the lifecycle and reproduction stages of marine creatures.
Also, in the past, destructive fishing practices have caused a lot of damage to the marine ecosystem although today this has stopped. One of the most imminent challenges today is climate change-related sea-level rise. To be sure, the sea level has already risen in many places causing erosion, higher tides and further inland crashing of waves.
Since Mauritius is highly dependent on its marine assets, different institutions play important roles in managing, monitoring and conserving these resources. The Mauritius Oceanography Institute has embarked on many projects such as coral farming and monitoring at various sites of the island to keep track of the status of coral reefs. The Fisheries Division also frequently sample coastal waters to ensure pollution levels are kept low. Furthermore, the Mauritius Research Council encourages marine research including seaweed farming to tap into scientific research on coastal resources. Also, Environmental Impact Assessments are required to initiate development in wetlands while Environmentally Sensitive Areas (ESAs) are protected in the Outline Planning Schemes.
In order to protect the marine biodiversity and conserve marine resources, several marine protected areas exist in the waters of the Republic of Mauritius. So far, there are 2 marine parks namely the Blue Bay Marine Park (3.53 km2) which is also a Ramsar site of international importance and the Balaclava Marine Park (4.85 km2). In addition to that, 6 Fishing Reserves, 5 Fisheries Reserved Areas, 4 Marine Reserves and a multiple Marine Protected area in the south-east of Rodrigues are managed.