WWW.WAS.ORG • WORLD AQUACULTURE • SEPTEMBER 2013 25 approaches that we have increasingly introduced with the modern forms of business aquaculture. In terrestrial farming a paradigm shift is needed to meet food production needs in the decades ahead, with limited land availability and especially scarce freshwater reserves for plant and meat production. Hydroponics integrated with highdensity fish farming in recirculation systems is being evaluated on various continents. Several research agencies are considering demonstration research of integrated farming of terrestrial and aquatic plants and animals, taking advantage of modern tools for sensor-controlled nutrient dosing and heat, energy and water recovery. However, moving away from monoculture will not be easy because the socioeconomic consequences of integrating different food production sectors requires important mentality shifts. Priority 8 –Marine Aquaculture. As mentioned previously, the oceans and seas make up 70 percent of our global aquatic bioresources. We cannot delay any longer to pay much more attention to the marine environment. It is an opportunity to satisfy seafood market needs and offer aquatic proteins as an alternative to terrestrial meat as a more sustainable food source for humanity in the decades to come. Several think-tanks have concluded that, by the middle of this century, there might not be enough fresh water to continue producing mammalian meat. The time has come to thoroughly reflect about future directions in coastal and offshore farming. To make a simplistic classification of present-day aquaculture practices, there is so-called “fed aquaculture,” e.g., the farming of fish and crustaceans in cages and ponds, and there is “extractive aquaculture,” with seaweeds removing inorganic nitrogen and phosphorus and filter-feeding mollusks grazing on organic nitrogen and phosphorus (Fig. 20). Pressure on the environment is very clear in open-flow pond farming of shrimp or fish (Fig. 21) or when trash fish (or formulated feeds) are used in high-density fish cages in shallow coastal waters (Fig. 22). The empirical practices established in a few coastal regions of China, where initially (starting in the 1950s) only seaweeds were farmed (Fig. 23), are instructive. Later, when mollusk seed could be produced in hatcheries, seaweeds and different mollusk species were grown together. Over the last decade marine fish cages have been added. Some of these areas are vast, encompassing tens of square kilometers of sea surface (Fig. 24). Nutrient flows in these polyculture systems are such that most of these habitats can be classified as oligotrophic environments. Multi-tropic aquaculture is definitely a part of the future but a lot of effort is required to motivate farmers and industries that operate today in a very competitive world. With what we see in China, we do not have to reinvent the wheel but rather should try to cooperate. Governments should be more proactive in facilitating demonstration projects in cooperation and joint management with private companies. China is furthermore experimenting with polyculture systems with benthic species – different mollusk, sea urchin and sea cucumber species – that benefit from nutrients accumulating under mollusk longlines or fish cages. The role of seaweeds in bioremediation (Fig. 25) is often overlooked. If the Chinese had not engaged in massive seaweed farming since the 1950s, when domestication and seed production of brown and red algae became feasible, coastal eutrophication today would have become much more critical. Close to ten million tons of seaweeds are harvested every year along China’s coast, equivalent to hundreds of thousands of tons of nitrogen and phosphorus that (CONTINUED ON PAGE 24) ABOVE LEFT, FIGURE 20. “Extractive” versus “fed” aquaculture practices. ABOVE RIGHT, FIGURE 21. Coastal shrimp farm in Thailand. LEFT, FIGURE 22. Coastal cage farming of yellow croaker in China (inserts: use of ‘trash’ fish as food source).
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