Right tool for the right job.  Which species of algae eater eats the invasive weed?  Hard to say, because w/out an infestation, then an introduction of a species that feeds primarily on the "invasive" weed, then a before and after analysis, we can't know the species to propagate because the food source would otherwise be kept in check unnoticed.

How about the smart folks at UH marine biology dept figgah out a commercially viable product or derivative from the algae.  But not one of those "it might be good used for x, but we need more funding to ensure...." kinda things.  Otherwise, just gotta pull 'em by hand again.