Sea Urchins are incredible powerhouses when it comes to clearing algae out of a reef. These echinoderms, related to starfish, venture around on their countless tube feet as they use their small, conical ring of ‘teeth’ to scrape algae, sponges, and other particulate foods off of most tank surfaces. Urchins are typically quite active and ravenous, and a single individual can make a huge impact on the presence of both encrusting and filamentous algae in both reef and fish-only systems. While reef-safe, it is highly recommended that any loose corals be glued down, as sea urchins in general have a tendency to accumulate objects to use as a sort of ‘cover’ from predators. If considering introducing an urchin to a fish-only system, be aware that some larger wrasse, trigger and puffer species are capable of consuming urchins.