What is growing on this coral?

[MacDuyver]

What is this purple web growing on the coral?

Location: Keramas Islands, Okinawa, Japan
Depth: 35-50ft
patch was about 9-12" wide, royal purple

 

[Germie]

Looks like a photosynthetic blue/purple sponge.

Did you found a lot there?

 

[MacDuyver]

Looks like a photosynthetic blue/purple sponge.

Did you found a lot there?

I’ve seen in on several dives. It’s not tremendously common, but it’s not exceedingly rare. It really stands out, it’s a really bold purple color.

I’ve been seeing a lot more dead coral covered with a leathery dark gray or black stuff lately (almost like coralline algae out of a horror movie, ), so I was curious if I’d found an early version of it.

I also want to make sure I have the right ID and tone to my text when I post it