Some corals have lived for centuries at the fringes of Mauritius. Now smothered for days in heavy fuel oil spilled from a wrecked Japanese ship nearby, parts of those reefs may be in trouble.The full impact of the toxic spill is still unfolding, scientists say. As the Indian Ocean island's residents scramble to mop up the oil slicks and clumps, they are seeing dead eels and fish floating in the water, as fuel-soaked seabirds limp onto shore.Satellite images also show the 1,000…