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Chinese aquaculture has employed a balanced ecosystem approach for freshwater aquaculture for several thousand years. Utilizing species that feed at different levels of the food web has permitted China to have the largest freshwater aquaculture production in the world. This production has proved to be sustainable in the long run because there is balance in this system. This concept is just starting to be thought of for broader aquaculture, including marine operations at sea or on land, and fishery communities around the world.

The National Oceanic and Atmospheric Administration has developed a Sustainable Fisheries Implementation Plan that recognizes three key elements - fisheries, aquaculture and coastal communities - for obtaining sustained production of seafood in the United States. The concepts of carrying capacity for biological activities in  a hydrographic system; ecological balance between primary producers, primary and secondary consumers; and nutrient flows in ecosystems are essential elements for the future development of world aquaculture and fisheries.

This chapter documents the present status of selected polyculture systems being employed by the aquaculture industry, provides examples of balanced ecosystem approaches to aquaculture and fisheries, and examines the question of how to develop models for maximizing the production of seafood through fisheries and aquaculture working in harmony to minimize environmental impacts.

Giant kelp (aka macro algae) are among the most prolific producers of biomass, growing in enormous underwater forests up and down the west coast of North America. For years kelp have been eyed as a source of biofuels. On November 24, 2015, one San Diego company received an award from the Department of Energy’s (DOE) Advanced Research Projects Agency-Energy (ARPA-E) to give their unique cultivation technology a run at producing biocrude from seaweed.

Sargassum macrocarpum is a rich source of anti-inflammatory compounds. Recently, one of the compounds, tuberatolide B, has been reported as a functional anti-inflammatory additive for foods and nutraceuticals. The artificial seeding, growth and maturation of S. macrocarpum were investigated from May 2018 to September 2019. Indoor culture experiments for induction of egg release were conducted at temperatures of 17, 20, 23, and 26°C and irradiances of 0, 10, 20, 40, and 80 μmol photons m-2 s-1 under 14 : 10 h (L : D) photoperiod. Within a given treatment combination, higher temperatures and irradiance levels favoured the maturation of receptacles in S. macrocarpum. Using artificial temperature and irradiance control, thalli matured one month earlier than thalli in nature. Under natural condition, receptacle formation began in April, and the eggs were released in June and July. The release of eggs from the receptacles was promoted at 17-20°C and 40-80 μmol photons m-2 s-1, and the fastest growth of germlings occuring at 15-17°C and 40 μmol photons m-2 s-1. For mature thalli, 300 g wet-weight was sufficient to seed 100 m of seed string. Thalli grew to 10.5 ± 2.6 cm in length at a density of 6.7 ± 3.3 individuals m-1 after 1 year of cultivation, from germination. This study demonstrates that it is possible to cultivate S. macrocarpum for the production of anti-inflammatory products.

The magnitude and character of nitrogen fixation in Sargassum communities was studied for three different species, S. fluitans Borgesen, S. natans J. Meyen and S. filipendula C. Agardh. Nitrogen fixation activity was measured using the acetylene reduction technique. The character of epiphytic populations on the surface of Sargassum was investigated by scanning electron microscopy. All three species of Sargassum exhibited the potential for high levels of acetylene reduction. Mean rates of up to 7.1 μmol C2H4 produced·g−1 (Sargassum dry wt.)·h−1 were observed at one location. Nitrogen fixation activity was strongly light dependent. Saturation light intensity for nitrogen fixation was low, i.e. < 100 μE·m−2·s−1, and no photoinhibition was observed under full sunlight intensity (i.e. photon flux of ≈ 2000 μE·m−2·s−1). Results indicated that cyanobacteria were responsible for nitrogen fixation. Both Calothrix and LPP type cyanobacteria were commonly represented on the surface of the Sargassum. Activity associated with the benthic species S. filipendula exhibited significant seasonal variability. Nitrogen fixation activity in pelagic samples was variable but high throughout the year. The contribution of nitrogen fixation to the nitrogen budget of Sargassum communities appears to be particularly pronounced in the pelagic environment.