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 (7-18 days) experiments with two Integrated Multi-Trophic Aquaculture (IMTA) systems (27.4 m2, 20 m3 each) stocked with the Pacific white shrimp, Litopenaeus vannamei, and the macroalga Gracilaria tikvahiae. Feed input totaled 67.5 kg with 4.3 kg of nitrogen. Shrimp yield was about 11.75 g m− 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 (2.0 kg m− 2/CV of 54.0%), ammonia-N flux (3.0 g m− 2  d− 1/CV of 90.2%) and total dissolved inorganic nitrogen flux (69 g m− 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 (98.6 g FW m− 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 (0.83 g m− 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.