|Coralline algae, in water. The green stuff is green algae, growing on the branches.|
These look like coral, but are actually a seaweed, one of the red algae. They collect calcium carbonate from the seawater, and incorporate it into their cells, where it becomes almost an exterior "shell". This seems to serve to protect them from algae eaters, from snails to crabs and hermits.
Only a few species of mollusk, such as the whitecap limpet or the lined chiton feed on coralline algae. (From U. of Oregon)
It's a red algae, but the calcium whitens it, turning it pink while it's alive. As it dies, the colour bleaches out until only the white chalk remains.
|Dry, on a little ceramic plate. The pink is already fading.|