Articles

Will the Oceans Help Feed Humanity?
CARLOS M. DUARTE, MARIANNE HOLMER, YNGVAR OLSEN, DORIS SOTO, NÚRIA MARBÀ, JOANA GUIU, KENNY BLACK, AND IOANNIS KARAKASSIS

Constraints on the availability of freshwater and land plants and animals to feed the 9.2 billion humans projected to inhabit Earth by 2050 can be overcome by enhancing the contribution the ocean makes to food production. Catches from ocean fisheries are unlikely to recover without adequate conservation measures, so the greater contribution of the oceans to feeding humanity must be derived largely from mariculture. For the effort to be successful, mariculture must close the production cycle to abandon its current dependence on fisheries catches; enhance the production of edible macroalgae and filter-feeder organisms; minimize environmental impacts; and increase integration with food production on land, transferring water-intensive components of the human diet (i.e., production of animal protein) to the ocean. Accommodating these changes will enable the oceans to become a major source of food, which we believe will constitute the next food revolution in human history. Keywords: aquaculture, food, animals, plants, bottlenecks

T

he human population is projected to reach 9200 million

by 2050 (UN 2007), which is within estimates of the maximum carrying capacity of the planet (Cohen 1995). A fundamental question for science is whether it is possible to increase food production to meet the demands of a human population of that magnitude. There is little room for optimism. Available water resources appear insufficient for agriculture to meet the food demands of 9200 million people (Cohen 1995, CAWMA 2007). The present population already experiences water stress (CAWMA 2007), which is exacerbated by the interactive effects of population growth and climate change (Vörösmarty et al. 2000). In addition, global fisheries landings have been declining since the mid-1980s (Pauly et al. 2003), contributing to the current food production crisis. Under this scenario, marine aquaculture (hereafter mariculture), the food-producing sector least dependent on freshwater availability (Verdegem et al. 2006), will be enlisted to help feed humanity in the 21st century (Marra 2005). Global terrestrial production and marine primary production are comparable in magnitude (Field et al. 1998), but marine food now contributes only 2% to the human food supply (FAO 2006a), as the development of controlled food production in the ocean lags several millennia behind that on land (Duarte et al. 2007). Aquaculture production currently faces important challenges (Diana 2009) that may hinder its future development. Because large-scale domestication of the ocean should be a mainstay of the

response to future food crises (Marra 2005), it is imperative to determine what is required to bring about this domestication. Here we build on recent analyses (Diana 2009) to examine the prospects for mariculture becoming a major force to meet growing human food demands, and we analyze the bottlenecks and challenges mariculture must overcome. Ceilings to agricultural food production Food sufficiency requires some 900 cubic meters (m3) of water per person per year (Falkenmark 1997), and about 9000 to 14,000 km3 per year are available for human use (Cohen 1995). Thus, a maximum of 10,000 million to 15,500 million people can be supported. Indeed, estimates of the maximum human population that Earth can sustain range from 6000 million to 15,000 million, with a median of about 10,000 million people (Cohen 1995). Far fewer people can be supported if less water is available for agriculture and nutrient requirements—particularly the fraction met by meat intake—increase. Indeed, the percentage of total water use co-opted by agriculture declined from 90% to 70% during the 20th century (FAO 2006a, CAWMA 2007), and agricultural production of nonfood commodities, such as cotton and biofuel, is increasing (CAWMA