Stable isotopes were determined in each sample by continuous-flow isotope mass spectrometer (Isoprime100, Isoprime Limited, Cheadle Hulme, UK) coupled with an elemental analyzer (Elementar vario MICRO CUBE, Elementar, Hanau, D). Each fragment (2.0–2.5 mg dry-weight) was analyzed individually. Isotopic ratios were expressed in ‘δ’ units as the relative difference (in parts per thousand)

between the sample and conventional standards (atmospheric N2 (Air) for 15N; PD-belemnite [PDB] carbonate for 13C) in accordance with the formula δR   (‰) = [(R  sample − R  standard)/R  standard] ∗∗ 103 ( Ponsard and Arditi, 2000), where R is the heavy-to-light isotope ratio of the element (R = 13C/12C or 15N/14N). learn more Results were monitored with reference to an internal standard calibrated to International Atomic Energy Agency reference materials (Caffeine: IAEA-CH6). Differences in δ15N values between T0 and T1 and among sites, and in isotopic enrichment between bathymetries and among sites, were tested by

t-test or Wilcoxon rank-sum test. The assumption of homogeneity of variances was checked using Cochran’s C-test, and data transformations were used where necessary. Spearman Statistical significance was evaluated at α = 0.05. The δ15N values of the macroalgae after 48 h of exposure were analyzed for spatial autocorrelation by Moran’s test with uniform spatial weights ( Cliff and Ord, 1981) and PD98059 price by distance-based nearest neighbour. Spatial analyses were performed using R software 2.15.2 (geoR and spdep package). In the reference area (Circeo), the initial N and C isotopic signatures (mean ± S.D.) of macroalgae were δ15N = 5.96 ± 0.54‰ and δ13C = −22.53‰ ± 2.04‰ in U. lactuca, and δ15N = 7.69 ± 0.39‰ and δ13C = −19.73‰ ± 2.43‰ in C. amentacea. After 48 h (T1), δ15N and δ13C values were not significantly different in U. lactuca ADP ribosylation factor ( Table 1; t-test, n.s.) whereas δ13C was greater in C. amentacea (t-test, p-value < 0.001). In the Gulf of

Gaeta, the isotopic signature of U. lactuca was δ15N = 5.71 ± 1.25‰ and δ13C = −22.26 ± 2.23‰ at start (T0) and δ15N = 8.15 ± 1.03‰ and δ13C = −22.42 ± 2.10‰ at T1. There was thus a statistically significant increase in δ15N ( Fig. 2 and Table 1; t-test, p < 0.001) and no significant change in δ13C (t-test, n.s.). The high 15N enrichment of U. lactuca was also evident in comparison with the reference area (Circeo) ( Fig. 2; t-test, p < 0.001). During 48 h of submersion in the Gulf, the coefficient of variation of N15 among replicate fronds of U. lactuca fell considerably, from 12.37% at T0 to 1.85% at T1 in the Vendicio area, from 23.73% to 6.76% in Formia, from 26.40% to 16.00% in Scauri, and from 14.70% to 6.03% in Garigliano. C. amentacea, which had higher starting values, was much less enriched in δ15N than U. lactuca after 48 h in the Gulf ( Table 1; Fig. 2).