The term "biokarst" refers to the bizzarely sculptured and corroded limestone
produced by combined activities of microbial endoliths, largely
cyanobacteria, and their grazers: gastropods, polyplacophors and, in
lower intertidal ranges, sea urchins. Dark coloration of otherwise
lightly colored limestone stems from cyanobacterial extracellular pigments, which
protects them from UV radiation.