This isn’t sea grass. This is a robust ghost pipefish (Solenostomus cyanopterus) that’s camouflaged in reef plant life. The video above was taken at a Gili Trawangan dive resort in Lombok, Indonesia. Plus, there’s more from Liquid Guru in Lembeh Straits, Sulawesi:
Robust Ghost Pipefish usually hang vertically in the water, not moving, pretending to be a bit of Sea Grass.
Here we have two males (the two smaller Pipefish) fighting over a female (the lager one with the lager pelvic fins). It was fascinating to watch and I ran out of bottom time before I could see who won.