What is this? (Algae maybe)

[JerryThomas]

The picture show my mespillia globulus with this kind of Brown leaf on it..I got another of this thing but bigger on one of my rock..you know what is this?

 

[Tahoe61]

Looks like Padina pavonica, scroll algae.

http://www.saltcorner.com/AquariumLibrary/browsegroupspecies.php?GroupID=96&filter=0

 

[JerryThomas]

That's it! Can I leave it or should I take it off?

 

[Tahoe61]

In a nutrient rich system it will spread. I had it appear once and I manually removed the small amount I had and it never came back.