I think this used to be an alchemy ingredient, for making a potion that transports you to Innothule Swamp, but since the alchemy revamp it may have no current use.
Incidentally, bladderwrack is the name of a real-world plant, and may have been the first source found for medicinal iodine. The name apparently does not refer to its effect on your bladder, but rather to the fact that the plant has air pockets (bladders) that allow it to float, like debris from a wracked ship.
In EQ, bladderwrack is not only sold at vendors, but it dropped (recently, i.e. after the alchemy revamp that made it obsolete) from a Sarnak Herb Collector in Chardok.