Towards a Marine Agronomy

There will be around 9.1 billion people on Earth by2050 who will demand more food than traditional agriculture may be able to provide because of limits on fresh water and arable land.  Might we look to aquaculture and the sea to provide more?

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 about 80 million metric tons per year (mmt/yr) of fish and shellfish, which derive from almost ten billion mt of phytoplankton through the marine food chain.

By comparison, on land we farm and harvest about 6,600mmt/yr 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, could a future ‘marine agronomy’ that farmed marine plants (macroalgae or seaweeds) as its primary crop become similarly productive? The resulting biomass would be used for food, feed and industrial feedstocks, as we use terrestrial plants now, and its possible use in fish feeds inspires a vision of a future self-sustaining marine agronomy where feed for farmed fish is made from seaweed grown for the purpose.

 Today, the only countries that farm seaweed on any scale are in Asia. China, for example, produces over 10mmt of seaweed annually with yields of one species, Laminaria, averaging 19.4 metric tons dry weight per hectare per year. 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 offers a perspective on the Earth’s potential productive capacity that suggests a bigger role for marine aquaculture than is now generally assumed. A vision for its future that embraces this idea may help policy makers and the communities they serve to better understand its possibilities.