Just though I would write something up on Live Rock as we have had a few 'newbies' show up lately.
Live Rock is an essential part of all aspects of marine aquariums - Whether it is a reef set up, FO (Fish only) or FOWLR (Fish Only With Live Rock).
Generally, live rock is the base structure for reef and FOWLR aquariums, providing a food source and shelter for your organisms and to provide a porous environment for essential bacteria. In fish only aquariums, live rock is generally found in the sump.
Live rock can come from four sources:
Dead base rock - dead coral rock placed into an aquarium with added ammonia to build up the essential bacteria
Oceanic Rock - 'Live' rock taken straight from a reef environment. This will contain the greatest quantity of higher life forms and the essential bacteria
Aqua-culture - Dead base rock which has been added to an aquarium with Live rock. This rock will have different marine algaes and some life forms such as copepods, in addition to bacteria
Mari-culture - Dead base rock which has been placed in the ocean. This rock contains the essential bacteria, and has an abundance of higher life forms. In essence, similar to oceanic live rock.
All of these different sources of Live Rock have different environmental and economic implications, as well as a cost factor for the average hobbyists. I will not go into these implications simply due to the fact that I feel that it is not my place to encourage or discourage people from buying from certain sources.
When people talk about live rock, they generally talk about the calcium skeletons of thousands of generations of SPS and LPS corals, covered in an abundance of life from copepods and amphipods, to worms, corals and even the occasional fish or octopus.
However, it is imperative to understand that the term Live Rock does not refer to different algaes or critters, but simply to the essential bacterial life contained within. For example, dead base rock placed into an aquarium and left to cycle with added ammonia, will become 'Live' but will not have any higher life forms than bacteria or lower algaes such as diatoms, cyano or possibly hair algae. However, it is fundamentally 'live' rock.
Rock taken out of the ocean is 'live' in the sense that it contains the essential bacterial life, but also has the added benefit of higher life forms such a copepods, worms and snails etc and different algaes such as coralline.
What people need to understand, is the importance of live rock to marine aquariums. The various species of bacteria which shelters within the rock eliminates dangerous ammonia, nitrite and nitrate. The rock also provided shelter for detritivores so that they are not predated on by your fish. These detritivores consume fish waste and are very beneficial to your aquarium. In essence, your rock is the 'filter' of your aquarium. Any any money which your would spend on a canister filter, should instead be invested in live rock.
As you can see, I have only discussed the basic principles of live rock. However, one must do their own research into what would work best for their aquarium. What so-called 'newbies' must understand, is that live rock is the basis on which your aquarium survives. It is also the filter which means that there is no need for expensive filtration equipment - EXCEPT FOR PROTEIN SKIMMERS