40 JUNE 2025 • WORLD AQUACULTURE • WWW.WAS.ORG ammonia to nitrite and nitrate, forms that plants can use. Marine RAS systems often use water from oceanic sources such as bays and inlets, filter and pretreat that water, and use it for culture. Capturing these nutrients with plants is desirable, and can reduce eutrophication. However, salt tolerant or salt loving plants are needed with marine waters. Some species can tolerate low to moderate levels of salt. Some varieties of kale and other greens have been documented as able to grow in salinities up to about 10 ppt (about 1/3 of ocean salinity). Recent studies at North Carolina State University (Pascual et al., 2024; Pascual, 2025) showed that Russian kale grows well to about 8-10 ppt and can still grow, although at a reduced rate, up to 15ppt (Figure 2 and 3). However, parallel studies on strawberries revealed that even 2.5 ppt can cause negative impacts on these and many other food plants. Strawberries were shown to respond well to intermittent low levels of salinity (2.5 and 4.5 ppt salinity, followed by fresh water, Figure 4). One interesting result was that strawberries grown in moderate salinity were measurably sweeter (Pascual et al., in press). Overall, RAS marine aquaponics may look like ‘traditional’ aquaponics, but with somewhat salty water. This saline water should also be considered when designing systems, since materials may rust or oxidize in these marine environments. RAS has the advantage FIGURE 2. Kale grown at different salinities showed good growth (Left: in number of leaves and Right: in biomass) up to about 8 ppt and reduced growth to about 15 ppt (from Pascual, 2025). FIGURE 3. Left) Kale grown at different salinities grew well to about 8 ppt and grew at a slower rate to 17 ppt. Right) Light levels were also shown to affect growth (photos: C. Pascual). Recirculating systems generally use settling and/or filtration to remove solids and may have biofilters to convert ammonia to nitrite and nitrate, forms that plants can use. Marine RAS systems often use water from oceanic sources such as bays and inlets, filter and pretreat that water, and use it for culture. Capturing these nutrients with plants is desirable, and can reduce eutrophication.
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