The coral reef is home to a huge variety of marine creatures, because it offers both shelter and food. Aquarists who place live rocks from the reef in their aquariums will soon see a number of marine invertebrates growing on these structures. Live rock typically consists of sandstone or coral skeletons, which have become encrusted with living creatures. To prevent dieoff, large invertebrate animals such as corals and sponges are normally removed from the rock before it is shipped, but spores and living tissue often remain. New life begins to develop once the rock has been placed in a correctly maintained saltwater tank.
Look closely at the rock for signs of pink or red colour. This colour consists of the first thin film of coralline algae cells. Coralline algae consists of a hard encrusting covering that may grow thick enough to form nodular ridges. This calcareous algae, which is composed of calcite shells, is particularly attractive and gives the rock a true coral reef appearance.
Observe the substrate and filter pipes and tubes for signs of red or pink colour as well. Although coralline algae originates on live rock, living cells will be carried around the aquarium, and this encrusting algae will soon establish itself on numerous sites in a correctly maintained saltwater tank.
Look out for tiny transparent jellylike nodules on the rocks, filter pipes and glass. These are baby aiptasia, or glass anemones. They tend to grow and spread extremely quickly, and most aquarists remove them from their aquariums or introduce aiptasia-eating fish such as the copperbanded butterfly fish or raccoon butterfly fish.
Examine the live rock for signs of sponge growth. Living sponge is found in a variety of colours, including yellow, blue and red.
Use a magnifying glass to identify the presence of living sponge, if necessary. Marine sponge is covered in pores and will look totally different to coralline algae, which will first appear as a hard, encrusting, thin film. Sponge tissue will appear to be softer.
Look out for tiny hollow bags that are attached to the rocks. These are tunicates, which may be growing in a small group or may be found as individuals. The single specimens look like tiny grapes or vases that are stuck to the rock.