But reef scientists say this flush of nutrients into the sea could harm nearby reefs and destroy the fisheries on which coastal communities now depend. "Coral reefs are extremely sensitive to nutrient pollution," says Mark Spalding, co-author of the UN-backed World Atlas of Coral Reefs. Sato "is working without external scientific advice and with no environmental impact assessment", he claims.
But Sato insists that, according to his own measurements, nitrogen and phosphorus levels round the mangroves are indistinguishable from those in the open sea.
The scheme has sparked a passionate debate. Some other marine ecologists contacted by New Scientist were vehemently opposed to the project, though they were not prepared to be quoted.
Sato, who retired as a cell biologist 11 years ago, has so far largely funded the project himself. In autumn 2002 his work in Eritrea earned him the prestigious Rolex award for enterprise, worth $100,000. He now hopes corporate sponsors will come in, to allow the programme to expand rapidly.
Mangroves along tropical shores nurture fisheries and help protect coasts from storms, and environmentalists are keen to conserve existing mangrove swamps. But, says Spalding, "in general, the success stories have been in areas where mangroves had previously flourished". Planting mangroves close to reefs could damage them, and "may threaten rather than support coastal livelihoods".