they are quite tasty apparently → http://www.pinktentacle.com/tag/jellyfish

“As part of an ongoing battle against invading swarms of giant jellyfish in local waters, some residents of Fukui prefecture have developed a method for converting the jellyfish into powder, which is used to make souvenir cookies. The jellyfish treats, called “Ekura-chan saku-saku cookies,” are now on sale at JR Fukui station at a price of 580 yen for a box of 10.”