Green Car Congress recently posted a story about an article in the magazine Oceanographydetailing a proposal to obtain liquid hydrocarbon fuels and protein for animal feed from large-scale industrial cultivation of marine microalgae (ICMM). Analysis indicates that coproduction of food and fuel is needed in order for algal bio-fuels to achieve production costs comparable to liquid fossil fuels. The authors argue that cultivation of marine micro algae is potentially an order of magnitude more productive (presumably per square meter of ocean cultivated) compared to biomass production on land. They further argue that the fact that salt water is used rather than fresh water can help to manage the demand on this important resource. They particularly emphasize the comparison of algal proteins to soy protein, maintaining that not only is the production more efficient but that the algal protein is potentially of higher quality. If ICMM is as efficient as projected then it may be possible to reforest marginally productive agricultural land thus leading to the removal some amount of CO2 from the atmosphere as well as helping to preserve land based bio-diversity.
Presumably intensive cultivation and harvesting of select species of marine microalgae over a large area will have negative effects on ocean bio-diversity, although this issue is not discussed in the Oceanography article. The authors do discuss the nutrient requirements of ICMM as as a sustainability issue. To achieve high productivity marine microalgae require a higher ratio of phosphorus to nitrogen compared to land based agricultural systems. The authors freely admit that the current use of rock phosphates in agricultural production is not sustainable in the long term and that nutrient recycling will have to be pursued. However, they argue that ICMM is very compatible with nutrient recycling since nearly 100% of the phosphorous in waste stream can be taken up and used by the microalgal population. This fact is in contradistinction to soil based agriculture in which nearly 80% of applied phosphorous is quickly transformed into stable forms which plants cannot utilize. Land which has undergone years of regular phosphorus applications has lots of phosphorus in it in stable forms that plants cannot digest. We may eventually be able to develop more complex system of agricultural production which utilize this phosphorus is place, but today’s highly productive (per acre and per labor hour) corn and soy bean rotations are not such a system.
My own view of the ICMM proposal is that it makes sense only if it is part of a long term plan to reduce the total human impact on the biosphere which includes other important effects in addition to green house gas emissions. We need to produce food for human beings, and if ocean farming can help us to do so with lower total impact on the biosphere then such a proposal is worth evaluating. However, if ICMM is being proposed in the context of a world of 10 billion human beings who expect constantly increasing standards of consumption (including such things as getting a large percentage of our protein from high on the food chain and frequent rapid travel over long distances) as a normal part of the operation of the economic system, then farming the ocean may just be one more step on the road to ecological disaster.