Environmental Profile

The island was formed in three distinct phases. The first phase was the emergence of the island from below the sea by massive volcanic eruption. The second and third phases combined high volcanic activity followed by erosion, during which time the northern plains and the northern shelf islets of Gunners Quoin, Flat, Gabriel Islands, Round and Serpent islands were formed. At this time the sea levels were 100 m lower and these northern islets formed part of the northern plain system.

Geography

Mauritius is 58 km from north to south and 47 km from east to west with an area of 1865 km2. The other island dependencies of Mauritius include:

• Rodrigues 600 km to the east
• St Brandon (Cargados Carajos) 460 km to the Northeast
• Agalega 1200 km to the north.

The topography of the island consists of a central plateau, which rises dramatically to the southwest with the highest point being Piton de la Petite Riviere Noire at 828 m. The central plateau is surrounded by the remnants of the primary volcanic crater system, including the second highest pint of Pieter Both at 823 m (the one with the boulder on top). To the north the island drops and flattens out to form the extensive northern plains extending down the west coast of the island as a coastal plain. The east coast has a very narrow to non-existent coastal plain with relatively steep topography rising from the coast.

The longest river on the island is the Grand Riviere Sud-Est which is 34 km from its head waters in the central plateau to where it enters the sea near Ile aux Cerfs.

Formation of coral reefs in Mauritius

In Mauritius corals started to grow in shallow waters parallel to the shore resulting in the formation of a fringing reef, covering 150 Km around the coast of Mauritius. In the southeast, at Grand Port/Mahebourg, there is a short stretch of typical barrier reef, while there are no reefs on the south coast. In geological terms a fringing reef is a relatively young reef. Fringing reefs protect the shoreline and the coral and seagrass habitats that develop within the lagoon. Reefs are very complex with different shaped corals forming ecological niches.

36 Genera and 90 species of hard corals have been recorded in the waters of Mauritius. Growth rates of coral colonies vary from 0.5 cm – 7 cm per annum and a football size coral head takes approximately 50 years or more to grow. As the coral colonies grow, the remaining skeletal forms of the organisms consolidate forming coral bedrock that is the foundation of the reef. The growth rate of a reef platform is dependent on environmental factors, but it is generally accepted to be around 1 cm per year.

Impacts on the lagoon and coral reefs of Mauritius

The impacts on the lagoons and coral reefs of Mauritius have been chronic and intense, starting 400 hundred years ago with the demise of the native forests, resulting in chronic sedimentation in the lagoons:

• Massive clearing of land for sugar plantations brought with it further sedimentation and associated pesticides and fertilizers being washed into the lagoons.
• The filling-in of what were extensive wetlands, which act as important natural filters has had severe impacts on the lagoons with polluted run off water directly entering the lagoon.
• Sand extraction for the construction industry, although now illegal, caused more sedimentation and erosion of the seagrass beds. Excessive sedimentation results in poor light quality, inhibiting coral growth and can also smother the coral, killing the colonies.
• Uncontrolled coastal and industrial development with associated pollution, dynamite fishing, and other negative forms of fishing such as the seine nets have all contributed as long-term stressors on the lagoons and reef systems.
• Tourism also has its direct and associated impacts, with snorkel and dive boats dropping anchors and breaking the coral. The collection of shells and corals for sale to visitors has depleted the number of shells and people holding, walking and sitting on coral all contribute to the demise of the lagoon habitats the visitors have come to see.