## 3 Results
### Natural \({}^{15}\)N and \({}^{13}\)C Values of Ultra spp. Stable isotopic ratios of N and C was monitored in _Ulva_ spp. cultivated in the lab-scale cultivation and in the pilot-IMTA systems during the cultivation periods tested. At lab-scale, _Ulva_ spp. was significantly enriched in \(\delta^{15}\)N after 24 days (LU1; d0 samples 12.49 \(\pm\) 0.27 vs. d24 samples 17.19 \(\pm\) 0.49), and after 8 days (LU2; d0 samples 10.64 \(\pm\) 0.43 vs. d24 samples 13.98 \(\pm\) 1.12) in fish effluent (_p_ < 0.0001; Table 5). The green macroalgae \(\delta^{13}\)C signatures were significantly depleted after 24 days (LU1; d0 samples \(-\)10.21 \(\pm\) 0.32 vs. d24 samples \(-\)20.48 \(\pm\) 1.02), and after 8 days (LU2; d0 samples \(-\)12.27 \(\pm\) 0.16 vs. d4 and d8 samples, \(-\)15.78 \(\pm\) 1.65 and \(-\)18.01 \(\pm\) 0.75, respectively) in fish effluent (_p_ < 0.0001; Table 5). By contrast, in the IMTA cultivation assays, no significant variation in \(\delta^{15}\)N values in the green macroalgae were observed during the experiments (Table 5, AQUA1 and AQUA2), except for the macroalgae collected in the estuary, becoming significantly depleted in \(\delta^{15}\)N from the beginning to the end of the experiment (AQUA1, d0 samples 12.85 \(\pm\) 0.11 vs. d22 \begin{table}
\begin{tabular}{l c c} \hline \hline  & \(\delta^{15}\)N/\({}^{14}\)N & \(\delta^{13}\)C/\({}^{12}\)C \\ \hline
**LU1-Late spring** & & \\ _d 0_ & 12.49 \(\pm\) 0.27 \({}^{\text{a}}\) & \(-\)10.21 \(\pm\) 0.32 \({}^{\text{a}}\) \\ _d 24_ & 17.19 \(\pm\) 0.49 \({}^{\text{b}}\) & \(-\)20.48 \(\pm\) 1.02 \({}^{\text{b}}\) \\
**LU2-Late autumn** & & \\ _d 0_ & 10.64 \(\pm\) 0.43 \({}^{\text{a}}\) & \(-\)12.27 \(\pm\) 0.16 \({}^{\text{a}}\) \\ _d 4_ & 11.79 \(\pm\) 0.04 \({}^{\text{a}}\) & \(-\)15.78 \(\pm\) 1.65 \({}^{\text{b}}\) \\ _d 8_ & 13.98 \(\pm\) 1.12 \({}^{\text{b}}\) & \(-\)18.01 \(\pm\) 0.75 \({}^{\text{b}}\) \\
**AQUA1-Late spring** & & \\ _ Estuary_ & & \\ _d 0_ & 12.85 \(\pm\) 0.11 \({}^{\text{a}}\) & \(-\)9.20 \(\pm\) 0.08 \({}^{\text{a}}\) \\ _d 8_ & 11.72 \(\pm\) 0.29 \({}^{\text{b}}\) & \(-\)8.18 \(\pm\) 1.40 \({}^{\text{a}}\) \\ _d 16_ & 10.51 \(\pm\) 0.52 \({}^{\text{c}}\) & \(-\)11.15 \(\pm\) 1.96 \({}^{\text{a,b}}\) \\ _d 22_ & 10.33 \(\pm\) 0.32 \({}^{\text{c}}\) & \(-\)13.10 \(\pm\) 1.16 \({}^{\text{b}}\) \\
**\#** & & \\ _Coast_ & & \\ _d 0_ & 9.40 \(\pm\) 0.17 \({}^{\text{a}}\) & \(-\)13.95 \(\pm\) 0.06 \({}^{\text{a}}\) \\ _d 8_ & 8.39 \(\pm\) 0.20 \({}^{\text{a}}\) & \(-\)14.58 \(\pm\) 2.37 \({}^{\text{a,b}}\) \\ _d 16_ & 8.99 \(\pm\) 0.55 \({}^{\text{a}}\) & \(-\)19.22 \(\pm\) 2.24 \({}^{\text{b}}\) \\ _d 22_ & 9.20 \(\pm\) 0.79 \({}^{\text{a}}\) & \(-\)17.94 \(\pm\) 1.65 \({}^{\text{a,b}}\) \\
**AQUA2-Late autumn** & & & \\ _d 0_ & 10.81 \(\pm\) 0.92 \({}^{\text{a}}\) & \(-\)14.46 \(\pm\) 2.30 \({}^{\text{a}}\) \\ _d 8_ & 11.39 \(\pm\) 0.30 \({}^{\text{a}}\) & \(-\)8.58 \(\pm\) 1.68 \({}^{\text{b}}\) \\ _d 14_ & 9.67 \(\pm\) 1.79 \({}^{\text{a}}\) & \(-\)11.78 \(\pm\) 3.76 \({}^{\text{a,b}}\) \\ _d 20_ & 9.79 \(\pm\) 1.06 \({}^{\text{a}}\) & \(-\)9.40 \(\pm\) 0.64 \\ _d 26_ & 10.13 \(\pm\) 0.65 \({}^{\text{a}}\) & \(-\)8.02 \(\pm\) 0.47 \({}^{\text{b}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Isotopic ratio of \({}^{15}\)N/\({}^{14}\)N and \({}^{13}\)C/\({}^{12}\)C obtained for: _Ulva_ spp., collected in _Mondogo_ estuary, cultivated in fish effluent, for 24 (late spring, LU1) and 9 days (late autumn, LU2), in a lab-scale cultivation system; _Ulva_ spp., collected in _Mondogo_ estuary and _Figueira da Foz_ coast in late spring and cultivated in fish effluent for 22 days (AQUA1) in an IMTA-pilot system; and _Ulva_ spp., collected in _Mondogo_ estuary, cultivated in fish effluent for 26 days (late autumn, AQUA2). Values are presented as mean \(\pm\) standard deviation, n = 3. Different letters indicate statistical differences. The symbol # expresses statistical differences between data regarding estuarine and coastal _Ulva_ spp. samples 10.33 \(\pm\) 0.32) (\(p\) < 0.05; Table 5). For \(\delta^{13}\)C, _Ulva_ spp.