sponge like thing growing on wooden deck

Hi folks,

I just noticed today this weird spongy algae?/fungus? growing out of the crack of one of my wooden planks on the deck floor. I had to peel it off as it had reasonable suction to the plank. Does anyone know what this is? I'm guessing this is harmful for the deck? Hoping to learn from the experts/more experienced folks here..
Thanks.