Is it animal or plant? Alive or not?
If you guessed a bryozoan, you are correct!
This is a kelp-encrusting bryozoan (Membranipora serrilamella). A bryozoan may look like a crystal of some sort but it is an animal that literally means “moss animal.” This species is a colonial species, so each small rectangular box you see is actually a compartment of silica surrounding an individual animal called a zooid! These filter feeders have mucous coated tentacles that help catch diatoms and other microscopic organisms to eat. They are commonly found on kelp, other types of algae, or rocks. If the algal host that they are on happens to die, they will also perish leaving behind their delicate silica patterns. Next time you’re down on the beach for low tide, see if you can find some of these bizarre creatures!
The crystalline crusts on these kelp fronds are the remains of colonies of bryozoans.