The best kind of invention is one that makes lemonade out of lemons. Jellyfish aren't quite taking over the world's oceans, but they are certainly causing big problems, enough for all kinds of original ways of reducing their numbers to have been proposed. The best that I've seen so far comes from research initially done at Tel Aviv University in Israel.
But let's start at the beginning: What's special about jellyfish?
The most obvious thing is that their bodies are 90% water, and they can hold this huge amount of liquid without disintegrating. This type of super-high absorption is exactly what we need in products like diapers, tampons, medical sponges, paper towels, etc.
So a startup called Cine’al is connecting the dots and claims to have found a way to turn jellyfish into something they call Hydromash, a "super-absorber” that can hold several time its weight in liquid and could be used in products that need the high absorbency. But unlike traditional super-absorbing polymers, it would both help fight back against the ocean invaders and be entirely biodegradable, taking about 1 month to break down. This biodegradability is a big deal, because landfills are full of diapers (we recommend trying cloth diapers, but not everybody does).
Of course, this is still not commercially available and could turn out to be vaporware, as so many things are. But the idea is certainly good, and I hope that it will be brought to fruition by someone, somewhere. Solving two problems at once is always nice.
But jellyfish aren't all problematic. Here's a good free documentary on these beautiful (at least underwater) creatures:
Via Times of Israel