The brown seaweed contain more minerals and iodine than the red and greens.
The green species only about 10% compared with the brown type seaweeds.
For the red species half the amounts of the brown like kelp and rockweed.

Indication:

Icelandic kelp, 8000ppm, Norwegian kelp 6000ppm, Atlantic kelp 2500-4000ppm,  

Pacific kelps 1000-1800ppm, Fucus spp. 200-500ppm, Wakame 50-150ppm, Sargassum 35ppm,

and Nori 15 ppm. These are all approximate and will vary considerably by season, location, age, a

and harvest practices.

The Japanese and other Asians usually rinse and soak their Kombu and other seaweeds in

freshwater for 10-30 minutes prior to using in miso broth and other cooking ,

which removes about 60% of the iodine (Hazutosi).

The soaking or prolonged rinsing of high-iodine content seaweeds may reduce the risks for

excess iodine-induced disease.