Below you'll find some sites that state that bladderwrack contains vitamin B12:

Remember that false information doesn't become a fact even if it many sources state the same thing - they might actually be quoting each other! Having said that, I can't see why bladderwrack should not contain B12...

Read more here:
The Health Professional's Guide to Dietary Supplements*by Shawn M. Talbott and Kerry Hughes
Evaluation of the contamination of marine Algae (Phaneuf D, Côté I, Dumas P, Ferron LA, LeBlanc A.)
Continence: Current Concepts and Treatment Strategies*by Gopal H. Badlani, G Willy Davila, Martin C. Michel, Jean De la Rosette