It's extra important if you are pregnant as a lack of iodine can lead to stillbirth, mental retardation, deaf mutism, dwarfism and neuromotor defects. Mostly sorted by iodizing salt - but it's an ongoing issue in parts of South Asia.

Also: just because something is labeled 'sea salt' that doesn't mean it has iodine.

That said, seaweed can be very tasty. I put it (wakame) in miso soup, fish soup, and often just munch on the flat sheets. Those are not calorie free but have some oil and salt - the oil is worth bearing in mind if you buy a lot and then it stays in the cupboard for months as the oil can go rancid.

You can find dried seaweed in Asian markets. I tend to avoid anything from China; they have good food regulations but those are often not enforced (what happens when the people in charge of enforcing can make profit when regulations are ignored). Anything from Japan or South Korea is good.

I started eating seaweed in the mid 60s. One of my friends on Bailey's Island (Gulf of Maine) was harvesting boatloads of what looked to be the same stuff I was used to seeing used to steam lobsters in a pit (the stuff with little bulbs that pop when you squeeze) - he was getting $$ for shipping it to Japan. I tried some just to see what the deal was - and have been hooked on the taste ever since.