That´s an interesting species, I think I haven´t seen it yet. When we lived on the Azores (Portugal), we often had like literally invasions of this jellyfish called the Portuguese Man O´ War. I cannot find the post that I wrote about them but here is the one that my girlfriend did...
Have you seen these too?
Holy shitballs!!!! Now that is an invasion, unreal!!! Kind of cool, but christ imagine getting stuck in between a few hundred of them, it would be the end of you, I'd say..
Actually, when they arrive in such amounts, it´s literally impossible to go in the water :) There are thousands of them (possibly millions) and their tentacles can reach up to 30 meters :D There is no way you could navigate through them...