It's water-borne or via contact (sick ones in tanks with healthy ones: within 24 hours of infection they die. First arms start tearing away; that is:
actively twisting until guts spill out and the arm 'walks' away. No culprit yet discernible.

Global warming related? pH of acidifying ocean(s)? hitch-hiker from some obscure locale? ... ...?
The end of starfish (or, also studied: a crustacean which hangs out with starfish; is it affected, a carrier?)

The end of the Beginning? Science shall be quite busy for the foreseeable, whether or not some folk believe in it or not. Add-to-list.

On a more positive note:
also this episode: some hi-tech investigations of making {superior} Chocolate! From DNA on to every aspect of processing. So much to learn.. could the ignorati ever catch up?