[thotpoizn]

This would make for an interesting experiment. Anaerobic digesters would presumably make short work of any toxin proteins, and you could probably get a fairly high jellyfish to "other" feedstocks [ratio] while retaining a commercially viable fertilizer (plus plenty of usable methane) as end products.

That said, I doubt that the cost to harvest and transport would be competitive with more conventional feedstocks such as slaughterhouse leavings, crop wastes / stalks, and plain old manure.

Food for thought, anyway. Floating digester platforms, maybe?

[edit: added missing word 'ratio']