Clean and green: A Californian kelp forest.

Credit: iStockphoto

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The dream of tackling climate change with biofuels has been tarnished by the rush to produce them on land. Not only are there serious environmental costs, including deforestation, water use, production of greenhouse gases, and energy-efficiency limitations, but there are also rising concerns about the effects on the world's poor.

Already the price of food is being driven up as land is taken away from food production, increasing the cost of food and nutrition for those who can least afford it.

It is curious then that, bar a brief mention in a recent paper on sustainable biofuels by the London-based Royal Society, the potential for biomass production at sea is largely ignored.

A vast resource

The oceans are the largest active carbon sink on the planet, covering more than 70 per cent of its surface area, and are predicted to grow as sea levels rise. Our seas also receive a larger proportion of the world's sunshine than land does, particularly in the tropical and subtropical belt where land is scarcer.

To agriculturalists, the oceans are vast and grossly underused fields well provided with sunlight and water.

Despite this, the full potential for sea cultivation (mariculture) has only recently been recognised. The 'blue revolution' of freshwater aquaculture and mariculture is growing exponentially.

Statistics from the U.N. Food and Agriculture Organization show mariculture is strongest in Asia and the Pacific. While aquaculture production has risen sixty-fold since the early 1950s (to 59.4 million tonnes in 2004) and is worth around US$70 billion (A$74 billion), 91.5 per cent of this was produced in Asia and the Pacific.

Similarly, 99.8 per cent of the eight million or so tonnes of seaweed produced each year, with a market of nearly US$6 billion, come from Asia and the Pacific, primarily China, Japan and Korea.

Seaweeds as fuel

Until now, seaweed has been valued mainly as food, but also as fertiliser, animal feed, and recently for a growing phycocolloid industry producing algin, agar and carrageenan. But it could also be a major fuel.

Macro-algae (seaweeds) are cultivated at sea, mainly by simply tying them to anchored floating lines. Seaweeds do not require soil, and are already provided with all the water they need, a major advantage over land production of biofuels since water is the most limiting factor for most agricultural expansion, especially with climate change.

One concern is that harvesting massive amounts of naturally occurring seaweed for bioenergy could have comparable effects on atmospheric carbon dioxide and habitat loss or fragmentation as large-scale deforestation. But cultivation is a different matter.

In Costa Rica and Japan, seaweed farming has been re-established to produce energy. It can quickly yield large amounts of carbon-neutral biomass, which can be burnt to generate electricity. High-value compounds — including some for other biofuels — can be extracted beforehand.

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