So, fungal spores are literally everywhere, and the requirements for fungus to thrive seem to be trivially low; give it a moderately humid environment and it’ll grow on a bare concrete wall ffs eating god only knows what; the dust from the air maybe?
Well, and the great outdoors is full of slightly damp places, many of them downright soggy most of the time - and absolutely rife with organic material to snack on.
Where’s the bottleneck? Why isn’t the world a choking fungal hellscape?
Hey, when barnacles are apparently friggin’ crustaceans, it’s sort of a fair question, I’d say.
Sea critters are weird.