I'm looking for a short story about an ocean planet where there are huge mats of algae and no other life. The algae appears dumb but on a cellular level it's running a simulation of another world, and life is evolving in the sim. Some of the life seems to be self aware.
I hope this is accurate, it's been years since I read it. I think I read this in either Asimov's or one of those big anthology books like The Year's Best Science Fiction.