Water scarcity may be the most limiting factor to increasing world food production. Irrigation water is already overdrawn beyond sustainable levels and to increase reliance on rainfed agriculture is risky, even more so with climate change. However, to promote deliberate food production at sea, both fished and farmed, and both plant and animal, requires no freshwater or land. The thousands of liters of freshwater needed to produce each kilogram of food on land are saved by producing at sea. Yet the ocean currently provides only around 2% of total food by weight. Even small rates of success in increasing food production at sea may represent the equivalent of massive freshwater gains, while the opposite is also true and decreases in marine fishing are costly in freshwater terms. If 10% of all ocean areas were eventually farmed, i.e. through mariculture, including extensive methods such as assisted fisheries and seaweed ranching, total yield could equal that currently produced in agriculture, and it might be more reliable. This would represent the equivalent gain of all the water already used in agriculture and about three times the water used for crop irrigation. Thus, it is essential to include deliberate production of food at sea and the concurrent freshwater gains in any policy discussions and documents on food and water.
Keywords: Assisted fisheries, Enhanced fisheries, Food production, Food security, Freshwater savings, Mariculture, Marine aquaculture, Sea farming