The oil spill off the coast of Mauritius has imperilled protected wetlands that boast rare mangrove forests and scores of fish and coral species.

The bulk carrier MV Wakashio, which struck a reef on July 25, has spewed more than 1,000 tonnes of fuel near two of Mauritius' three "Ramsar sites", named after the international convention to preserve wetlands.

Thankfully, salvage crews on Wednesday finished removing all the fuel that was in the vessel's tanks, though another 100 tonnes remained on board elsewhere.

Prime Minister Pravind Jugnauth has warned, however, of a high probability that the 300-metre (984-feet) vessel will break up.

Here's a look at the two sites:

Trace amounts of oil have been found at Blue Bay, a 353-hectare (872-acre) Ramsar site featuring 38 species of coral including spherical "brain coral" that is more than a century old.

That oil was "immediately contained" as part of clean-up operations, said Sunil Dowarkasing, a former Greenpeace strategist and environmental expert assisting in the clean-up.

Map of Mauritius, locating unique protected wildlife sites threatened by the fuel spill
Map of Mauritius, locating unique protected wildlife sites threatened by the fuel spill AFP / Gillian HANDYSIDE

But a larger intrusion could deliver a hefty blow to the site abutting tourist-friendly Blue Bay Beach, he said.

"If Blue Bay Marine Park is polluted then we are going to lose a jewel for Mauritius," Dowarkasing said.

Blue Bay's mangroves, seagrass meadows and macro algae provide a habitat "for about 72 fish species and the endangered green turtle, as well as a nursing ground for juvenile marine species", the Ramsar Convention notes on its website.

The shallow, brackish waters of the 22-hectare Pointe d'Esny site feature a mangrove forest, mud flats, threatened plants and native butterflies.

The area is more protected than Blue Bay, with a coastal road separating the mangroves from the nearby lagoon.

But mangrove roots are prone to trap oil, Dowarkasing warned, rendering Pointe d'Esny especially vulnerable if there is extensive intrusion.

Mauritius' third Ramsar site, the Rivulet Terre Rouge Estuary Bird Sanctuary, is located on the opposite side of the country's main island and is not threatened by the spill.

Oil Spill