All of the 650 species of seaweeds in the Salish Sea are edible with the exception of Desmarestia spp which is commonly referred to as ‘Witch’s Hair’ or Acid Kelp (yes, that would be sulfuric acid.)
However, iodine concentrations can vary from 16µg/g in Porphyra spp (or Nori) to over 8000µg/g in Laminaria digitata (marketed as ‘kelp granules’). The FDA has set the acceptable daily intake of iodine for adults from a minimum of 150µg/day to a maximum of 1100 µg/day (200µg/day for toddlers). So while most wild harvested seaweeds are edible (and delicious) please be careful if wild harvesting or, better yet, purchase them from a reputable seaweed monger who will provide you with nutritional data.
These plants are an excellent source protein, functional fiber, amino acids and trace minerals, including iodine. Blanching, sun drying and other techniques lower the iodine values and some contain T4 precursors that can greatly benefit those with thyroid problems. Dr Ryan Drum is a local treasure in the San Juan Islands and we highly recommend those with questions about thyroid function and purchasing edible Seaweeds to his website.
You can also find a list of concentrations of metals, nutrients and iodine in Bull Kelp here.