New mangrove forests threaten coral reefs

New mangrove forests threaten coral reefs

30th April 2003

Fred Pearce - New Scientist

An audacious scheme to plant the world's desert coastlines with mangrove trees is being condemned by marine biologists as a potential disaster for coral reefs.

The scheme is the brainchild of a retired US cell biologist, Gordon Sato. He wants to plant mangroves along hundreds of kilometres of coastline in Mexico, Arabia and elsewhere. His first 250,000 trees are already growing close to coral reefs on the shores of the Red Sea in Eritrea.

"The object is to create whole new forests of mangrove trees in vast areas of the world," says Sato. He believes that mangroves will fight poverty by providing fodder for goats, and help combat global warming by absorbing carbon from the air.

Sato estimates he could plant 50 million trees round the Red Sea alone, and 200 million on the shores of the Gulf of California in Mexico. If canals were used to take seawater inland, much of the Sahara, the Arabian Peninsula and the Atacama Desert of Chile could be planted, too. "Such forests would banish the problem of global warming," he says.

The mangroves will be planted on beaches between the high and low water mark. To help them grow, Sato is adding up to a tonne of fertiliser per hectare of beach, placed in the sand in small bags that slowly release the nutrients.

Nutrient pollution

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".