The recirculating aquaculture system (RAS) present as a solution for Singapore’s strive for greater food security and resilience. Being technologically driven, RAS allows for the intensification of production without the reliance on favourable environmental conditions. However, the current impediment of the RAS is the build-up of nitrate. High nitrate level (>50 ppm) is
d etrimental to fish health. Traditionally, this is dealt with
through partial water exchange. As macroalgae require nitrate for growth, the farming of macroalgae could potentially serve as cheaper alternative for nitrate removal. However, high stocking density in RAS could cause pH to drop. The effectiveness of nitrate removal by macroalgae under low pH condition of RAS is currently unclear.
How might these change due to climate change is also unknown. Using a random block design, we investigated the nitrate uptake in two commercially important species under different pH and temperature regime. Our analyses suggest that, in general, the efficacy of macroalgae in nitrate removal decrease as pH decrease and temperature increase. While macroalgae could be used to remove nitrate in RAS, they are unlikely to be effective in high stocked RAS. The efficacy of macroalgae in removing nitrate is also probably going to be affected by climate change.