Nitrogen biofiltration capacities and photosynthetic activity of Pyropia yezoensis Ueda (Bangiales, Rhodophyta): groundwork to validate its potential in integrated multi-trophic aquaculture (IMTA)

Porphyra spp. (currently Porphyra and Pyropia) are major sources of seafood globally. In this study, we investigated the effects of ammonium concentration, water temperature, and thallus stocking density on N-ammonium uptake rate (NUR), tissue nutrients content, N-NH4 (+) filtration efficiency (NUE: nitrogen uptake efficiency %) of Pyropia yezoensis at a laboratory scale and in a mesoscale to evaluate the potential of this species as a biofilter. Additionally, photosynthetic activity was examined using Diving-PAM fluorometer to evaluate the health status. At a laboratory scale, the NUR and tissue nitrogen (N) content of P. yezoensis increased with increasing NH4 (+) concentrations in the medium. The NUR at thallus stocking densities of 5 and 10 g fresh weight (FW) L-1 were significantly higher than that at 20 g FW L-1. Effective quantum yield (a dagger F/F' (m) ) and tissue N content was significantly higher at all stocking densities than that at the beginning of experiment. The NUE was over 90 % at 10 and 17 A degrees C, while all thalli cultured at 25 A degrees C died after 5 days. In a mesoscale, the NUE at a thallus stocking density of 10.0 g FW L-1 was significantly higher than that at a stocking density of 5.0 g FW L-1. No differences in the NUE occurred between 10 A degrees C and 17 A degrees C. Photosynthetic activity (a dagger F/F'(m) and rETR(max)) of P. yezoensis at optimal culture condition (10-12 A degrees C and 10 g FW L-1) increased over time through the experiment. This indicates that thallus was healthy during culture and chlorophyll a fluorescence can be as a monitoring tool for evaluating the physiological status of seaweeds in an integrated multi-trophic aquaculture.