Diadema sestosum is one of the best generalized grazers. It is a very through grazer, often grazing down through coraline algae and into the white carbonate rock. It will graze more types of algae than most grazers, but IME prefers red algae, especially red wire algae and coraline algae. There are some algae it seems to avoid, like red cotton algae (Asparagopsis) and Sargassum.
It comes small but grows quickly. It is fast-moving for an urchin and quite agile. The long spines penetrate the skin easily and break off to leave a painful tip under the skin. Several types of fish use Diadema spines as protection from predators in the wild. Larger urchins may sample certain stony coral but IME rarely do much damage. Poorly secured fragments will be knocked off by a Diadema, very small and fragile fragments could be eaten. Diadema will accept meat food like frozen Mysis shrimp. I had one Diadema trap a Mandarin while it was in its nightly stupor and kill it, eating it tail-first when I found it.
The best single herbivore I've come across. Its a beautiful and active creature that usually catches a visitor's attention.
