Of all the trace elements found in natural sea water, iodine is associated with the widest range of effects. Iodine prevents goitre as an important component of the thyroid hormone. It also is essential for the hardening of the chitinous shell of crustaceans. Coralline algae deposit iodine in surface structures and gorgoniias deposit it in the axial skeleton. Brown algae also strongly accumulate this trace element.