I grew up in Cocoa Beach in the 70s and I can remember it happening occassionally that the jellyfish would come in like this and inundate the beach. Anyone who went swimming was sure to get stung but the stings are minor and can be taken out with vinigar or even a paste made of MSG. Those kind were not such a big deal but when the Portugese Manowar jellies came in that was nasty, their sting is very bad and they have long long tenticles that end up tangling up all around you so it is not just one or two stings but numerous ones all over your body, wherever the tenticles touched you. I can also remember having a red tide and they advised everyone against going in the water. Red tide is an algae bloom but the algae give off some sort of toxin when they go haywire like that. This is nothing new. It is cyclic.