| Summary: | The present study evaluated a polyculture system with Pacific white shrimp (<i>Litopenaeus vannamei</i>) and the macroalga <i>Gracilaria birdiae</i> and its potential to remove nutrients. The experimental design consisted of a shrimp monoculture of 100 animals/m<sup>2</sup> (T0) and three multitrophic cultures with <i>L. vannamei</i> (100 animals/m<sup>2</sup>) and with <i>G. birdiae</i> at densities of 500 (T500), 1000 (T1000), and 2000 (T2000) g/m<sup>2</sup>. Nitrogen and phosphorus concentrations decreased at the beginning of the experiment in the treatments with macroalgae, but this reduction was not maintained throughout the cultivation period. The stable values of <i>G. birdiae</i> biomass were perhaps related to the high turbidity of the water. There was an increase in shrimp biomass during cultivation, which reached the final individual averages of 7.5 g (T0), 7.6 g (T500), 5.9 g (T1000), and 7.5 g (T2000), with no significant differences between treatments. Nevertheless, the absence of macroalgae growth provides no added profit for the producer. Thus, there is no economic advantage in using <i>G. birdiae</i> in an integrated multitrophic system with <i>L. vannamei</i> at a high density and conditions of high water turbidity.
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