I know it's hard to get a good pic of it but if u get a close up pic of the blue Algae maybe it will be Easyer to ID. I don't think we r trying to tell u ur wrong about it being algae cuz u very much so could be right. My thought is that Iv never seen or Heard of blue coralline so my opinion is its more likely not algae. But I get all kinds of sponges hitchhiking on my stuff. I have every color of the rainbow in sponges. So the likelihood of it being a sponge rather than algae is a lot more high. But that's my opinion. And like I said I could be wrong. That's why a closer pick mite help.
