Growth and nutrient uptake of the macroalga Gracilaria tikvahiae cultured with the shrimp Litopenaeus vannamei in an Integrated Multi-Trophic Aquaculture (IMTA) system

Nutrient uptake and macroalgal growth performance were studied in short term (7-18days) experiments with two Integrated Multi-Trophic Aquaculture (IMTA) systems (27.4m², 20m³ each) stocked with the Pacific white shrimp, Litopenaeus vannamei, and the macroalga Gracilaria tikvahiae. Feed input totaled 67.5kg with 4.3kg of nitrogen. Shrimp yield was about 11.75gm^-2 d^-1 and survival surpassed 98%. Temperature dropped with the season (from 33 to 18°C). The experimental variables of water turnover rate (mean of 3.3 d^-1/CV - coefficient of variation - of 72.7%) in the shrimp tanks, stocking density of the algae (2.0kgm^-2/CV of 54.0%), ammonia-N flux (3.0gm^-2 d^-1/CV of 90.2%) and total dissolved inorganic nitrogen flux (69gm^-2 d^-1/CV of 95.5%) through the algal troughs also varied between trials. The ensuing performance envelopes (means and CV's) were determined for algal growth (98.6gFWm^-2 d^-1/CV of 67.2%), specific growth rate-μ (4.8% d^-1/CV of 87.2%), algal tissue N content (5.7% N in DW/CV of 9.9%), C:N ratio (g/g) in the algal tissue (4.8/CV of 7.2%), and areal rate of N incorporation into algal tissue (0.83gm^-2 d^-1/CV of 62.1%). The study demonstrates the biological and technical feasibility and the operation-performance envelope of the studied shrimp-macroalgae IMTA system. A rudimentary nutrient budget suggests a recovery of nearly 35% of the nitrogen input by shrimp and algal biomass. Additional refinements could raise further the fraction of feed N that is recovered in shrimp and algal yields.