Aquaculture is an established technique for producing marine species. However, it creates large amounts of nutrient-rich waste. Therefore, it is worth examining the methods available to use these nutrients and close the nutrient cycle. This review covers research activities of different saline water methods for food production.These are Integrated Multi-Trophic Aquaculture (IMTA), Biofloc Technology (BFT) and marine aquaponics. IMTA combines on-and offshore aquaculture with macroalgae and filter feeder production. Commercial implementations have been achieved but are not widely used. Especially shrimp are suitable for cultivation in saline BFT systems. Few commercial deployments exist. There is a well-established market for the products of IMTA and BFT systems. Marine aquaponics is increasingly being tested as part of an expansion of Recirculating Aquaculture Systems (RAS) and BFT systems, but commercial implementations are not known. Moreover, there is no established market for the resulting salt-tolerant plants (halophytes). Market prices and popularity were evaluated to assess the economic potential of the different plant and aquaculture species farmed with IMTA, BFT and marine aquaponics. There are established markets for well-known products, but therefore the competition is greater. Niche products are offered occasionally, but often achieve top prices. Closing nutrient cycles and increasing saline water usage for food production as well as high product diversity are necessary to mitigate the increasing pressure on freshwater resources and to be able to feed the growing world population. Therefore, IMTA, BFT and marine aquaponics are promising techniques for reducing pressure on freshwater resources and improving food supply.

Hydroponic systems have the potential for being one of the most promising sustainable alternative methods of food production, where they confer the advantages of producing higher yields with better control over plant growth. The main purpose of this study is to determine differences in growth rates, sensory attributes and nutrient uptake upon growing lettuce (Lactuca sativa L.) in various hydroponic subsystems at two different plant spacings. We investigated the interaction of different effects on lettuce growth in four hydroponic subsystems, Deep Water Culture ((DWC), Nutrient Film Technique (NFT), Media- Bed system (MB) and Sandponic (SP), at two different plant densities, at narrow planting spacings (20 x25 cm), and larger planting spacings (24 x 25 cm). Our findings show that cultivation methods and planting spacing greatly influence lettuce growth. Overall, the present study provides direct evidence that DWC and NFTs subsystems at both planting spacings performed the best in terms of giving higher yield production, higher plant growth parameters, and better sensory attributes compared to other cultivation systems. Lettuces grown in the DWC system had higher chlorophyll B (29.13 ± 0.82 mg/100 g), and carotene content (32.40 ± 1.27 mg/100 g) in narrow planting spacing and were the most preferred lettuces according to taste tests (52.4%).

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