The pelagic Sargassum bloom might be responding to nutrient enrichment of ocean waters; and the massive amount of biomass might be an opportunity to commercialize this resource. Safe use needs to be tested due to the metals’ biosorption ability of Sargassum. Here we present nutrient and trace metal tissue content of pelagic Sargassum collected in South Florida. Samples of S. fluitans, and S. natans collected from three localities in the Biscayne area were cleaned, dried for 48 h at 68oC, and ground. Analysis were conducted at analytical facilitates at FIU. Mean N tissue content was 1.08 + 0.23 and mean P was 0.0348 ± 0.0122. No deficit of nutrient content compared to global mean values for macrophytes were detected. The C:N ratio of 43.15 + 7.43, and the C:P ratio of 3175 ± 1039 show a high content of C relative to N and P. The N:P ratio of 66+24.35 show a limitation of P content relative to N. The stoichiometric C:N:P ratio of 3175 ±1039: 66±24.35:1 of the South Florida samples compared to the global average of 1,106:38:1 demonstrate a large content of C and N. We suggest that an increase on C availability together with N should be explored as potential causes triggering this macroalgal mega bloom. A high variability in metal concentrations was found, it is noteworthy that arsenic was found in high concentrations in all samples ranging from 73 up to 120 ppm. The characteristic presence of alginates in brown algae, particularly in Sargassum, increases the affinity of species of this genus for trace metals. Variability might reflect individual physiological conditions as well as metals’ availability along the trajectory of these pelagic species along the Atlantic. We suggest requesting estimations of tissue metal concentrations before approving Sargassum for human or animal consumption.