Nutrient and toxicant levels as well as their bioavailability in S. latissima and Ulva species (fenestrata, intestinalis, rigida) were reviewed. Nutritional quality was assessed by nutrient contribution to daily reference intake (DRI) per portion (5 g dry weight), nutrient density score NRF21.3, and comparisons to reference foods. Toxicological assessments comprised tolerable daily intake (TDI)-levels. Based on mean %DRI per portion, S. latissima and Ulva species were good sources (%DRI >15) of calcium, magnesium, iron, selenium, and vitamin B12. Mean %DRI was <10% for fiber, sodium, and protein. Toxicological concerns were mainly due to iodine (mean %TDI per portion: 3160% for S. latissima and 41–91% for Ulva species). Mean %TDIs for inorganic arsenic, cadmium, and lead were <20% for S. latissima and 9–97%, 6–15%, and 21–46%, for the selected Ulva species, respectively. Bioavailability data were scarce and is, together with nutritional impact of processing, an important aspect to address in future studies.