White net-like strings on rocks?

[EricL.]

Hey,
recently, these white stripes appeared on one of my rocks. They seem to be a single network at first glance, but there are also many unconnected parts to them.
Could be some sort of sponge?

Btw, I really like the bright green color that my rocks seem to transition to!

 

[Ron Reefman]

Sponge was my first thought as well. And don't be surprised if they disappear after a3 to 6 more months.