It’s time to make more productive use of the sea, says John Forster.

John Forster

What should we expect from marine aquaculture in the future? Will it serve simply to top up supplies of fish and shellfish from capture fisheries, as it does now and as is mostly assumed, or does it promise something more?

There will be around 9.1 billion people on Earth by 2050 and traditional farming might not be able to produce enough food for them. Limited fresh water and arable land will constrain agricultural growth, while growing affluence in developing countries will add to the challenge as people eat more meat or turn food crops into biofuel. Therefore, ‘Will the oceans feed humanity?’ (PDF)

Oceans cover 70% of the Earth and contain 97% of its water, yet they yield less than 2% of our food. This is not because they are unproductive; it is because we cannot harvest the phytoplankton that represents the vast bulk of marine productivity.

Instead, we harvest fish and shellfish, which derive from phytoplankton through the marine food chain. Since each link in the chain retains only about 10 percent of its food energy as growth, the biomass of the larger animals we catch reduces sharply. For example, the 83 million metric tons (mmt) of fish landed each year by the world’s commercial fisheries derive originally from over 10,000mmt of phytoplankton because there are an average of 3.1 links, or conversion steps, between them and the phytoplankton from which they originally derive.

By comparison, on land we farm and harvest about 6,600mmt per year of plants most of which we eat directly, much of the rest being fed to farm animals to produce meat and dairy products. This terrestrial agronomy produces over 98% of our food from cultivated lands that comprise 24 percent of the Earth’s terrestrial surface.

Therefore, a question for marine aquaculture is: can it become a similarly productive marine agronomy to ease the burden that future human generations will otherwise impose on the land?

To do so, marine plants (macroalgae, or seaweeds) must become the primary crop for food, feed and other applications as we use terrestrial plants instead of the marine animals produced now.

This is not a new idea. In 1968, an American physicist named Howard Wilcox offered his vision for ‘Ocean Food and Energy Farms’ off the coast of California and it was tested in what became known as the US Marine Biomass Program (Chynoweth, 2002). However, over-ambitious goals for bioenergy production, prompted by the oil crisis of the 1970s, were not met and the program lapsed as oil flowed freely again in the 1980s.

A sea change

Today, the only countries that farm seaweed on any scale are in Asia. China, for example, produces over 10mmt of seaweed annually (PDF) with yields of one species, Laminaria, averaging 19.4 metric tons dry weight per hectare per year (Chen, 2006). At this level, it would need only 1% of the Earth’s ocean surface to grow an amount of seaweed equal to all the food plants currently farmed on land.

Though extrapolations like this can be pushed too far, the idea that one day it might be possible to double our food supply by farming less than 1% of the oceans suggests that we have not yet thought hard enough about what marine aquaculture has to offer. That it might be done without using land or fresh water in a world that may be short of both makes the idea doubly attractive and, encouragingly, new initiatives are under way.

For example, the Biomara project will produce biofuels from marine biomass harvested from UK and Irish waters, while a similar project has just been announced in Chile between Norway’s Statoil and the U.S. company, Bio Architecture. Another new project in the UK will review the potential for marine micro and macroalgae as raw materials in aquaculture feeds.

Expectations for these projects should not be allowed to run ahead of themselves either, especially for those pursuing biofuel. Huge amounts of marine biomass are needed to produce any worthwhile quantity of biofuel at reasonable cost and large-scale seaweed farming methods still have to be perfected.

However, because food and feed products made from seaweed have higher sale values and can succeed commercially on a smaller scale, they may offer more immediate potential. Their production for processing into animal feed also inspires a vision of a future self-sustaining marine agronomy where feed for farmed fish is made from seaweed grown for the purpose, answering critics who voice concern about aquaculture’s present dependency on feed derived from industrial scale sea fishing and as well as alternate terrestrial feed ingredients.

All efforts to farm plants in sea, however, will expand marine aquaculture’s horizons and illuminate its promise. A vision for its future that embraces this idea will help policy makers and the communities they serve to better understand its possibilities.

About John Forster

John Forster has worked as an aquaculture scientist, manager, fish farm owner and consultant since 1965. He moved to Port Angeles, Washington, from the UK in 1984 to start salmon and sturgeon farming operations for Stolt Sea Farm before founding his consulting practice and Columbia River Fish Farms Inc. in 1994.

You may also be interested in: