On the log-strewn beach at Cape San Blas, we crossed over this pair. The one log was serving as a nursery for what I assume is an algae, and there is only a little on the other log. There was not any growing on the other side of the logs so orientation may be of importance.
The brown, animal-looking, vertical object is actually a palm stump.
I wonder if the white is dead from being dried out. There were hundreds of tiny barnacles sheltering under the algae.
If anyone has any more information, please share!