Monti - What is this growing underneath of it?

[1leftygolfer]

Gradually this white soft almost velvet feeling growth continues to grow underneath. Anyone have an ID for it? Thanks.

 

[Tahoe Reefer]

A type of sponge. I've got similar sponge growing in the shade, it's never harmed anything.

 

[1leftygolfer]

Cool. Thanks.