Seaweeds are high in iodine content as they grow in iodine-rich ocean water, although the amount can depend on where it is harvested. There is such a broad range in the iodine content of foods, including seaweed, that the USDA National Nutrient Database does not even include iodine in its nutrient breakdown.
A list of commonly consumed seaweeds and their iodine content per gram is published in a 2004 issue of Thyroid, and the content ranges from 16 micrograms in a 1-gram sheet of nori seaweed to over 8,000 micrograms in a 1-gram serving of fingered tangle granules.
The iodine content of a single sheet of seaweed can range from 16 to 3,000 micrograms, according to the National Institutes of Health Office of Dietary Supplements. If you purchase dried or powdered seaweed, check packaging for serving size and iodine content, if listed.