We see colonial diatoms on a white substrate. What is it?

Zoom out a bit to see the head of a scorpionfish!

This image was posted on iNaturalist by David Rolla. Thank you for sharing.

iNaturalist is platform for sharing observations of organisms. The platform is not only a great way to seek community feedback, but it is a means to document the occurrence of
a taxon at a particular place and time. If you are seeking a another great community (besides this one!) of naturalists in a supportive environment, have a look at the diatom entries in the application.