Integrating filamentous ‘green tide’ algae into tropical pond-based aquaculture

‘Green tide’ algae bloom in eutrophic environments with fast growth rates and efficient nutrient uptake. These same characteristics are sought after for algae in integrated aquaculture systems. We examined the effect of two key variables, salinity and total ammonia nitrogen (TAN), on the growth of three filamentous ‘green tide’ algae, Cladophora coelothrix, Chaetomorpha indica and Ulva sp. Survival and growth were first determined across the extremes of salinity in ponds (0 to 45‰). Subsequently, the interactive effects of salinity (15, 36 and 45‰) and TAN (0–700 µmol l−1) were quantified using a factorial design. All species have a broad tolerance to salinity (ranging from 5 to 45‰) with each having a different optimum for growth (C. coelothrix 30‰, C. indica 20‰ and Ulva sp. 15‰). A significant interaction (salinity⁎TAN⁎species) further demonstrated that responses vary between algae. C. indica and Ulva sp. have their highest growth rates of ~14% day−1 and ~25% day−1 respectively at higher TAN levels (>70 µmol l−1) but at different salinities. Growth of C. coelothrix was optimum at lower TAN levels (35 µmol l−1) and 36‰, but surprisingly was inhibited at the highest TAN. C. coelothrix and C. indica were also cultured in an operational bioremediation pond. High growth rates of C. coelothrix were maintained in situ (~6% day−1), while C. indica performed poorly. Finally, TAN removal rates were calculated using natural densities and in situ growth rates demonstrating that ‘green tide' algae have broad application across the environmental variables that characterize tropical pond-based aquaculture.