Live rock

"Live rock" is rock from the ocean that has been introduced into a saltwater aquarium, which confers to the closed marine system multiple benefits desired by the salt water marine hobbyist. The name sometimes leads to misunderstandings as "live rock" is itself not actually alive, but is made simply from the calcium carbonate skeletons of long dead corals, or other calcareous organisms, which in the ocean form the majority of coral reefs. When taken from the ocean it is usually encrusted with Coralline algae and inhabited by a multitude of marine organisms. The many forms of micro and macroscopic marine life that live on and inside of the rock, and which acts as an ideal habitat, give it name "live rock."



Purpose of Live Rock
For the aquarium trade this rock is highly valued not only for the diversity of life it can bring to the closed marine environment, but its function as a superior biological filter that hosts both aerobic and anaerobic nitrifying bacteria required for the nitrogen cycle that processes waste. Live rock becomes the main biological nitrification base or biological filter of a saltwater aquarium. Additionally, "live rocks" have a stablizing effect on the water chemistry, in particular on helping to maintain constant pH by release of calcium. Lastly, live rock, especially when encrusted with multiple colors of coralline algae, becomes a major decorative element of the aquarium and provides shelter for the inhabitants. It's often used to build caves, arches, overhangs, or other structures in the tank, an art known as aquascaping. Live rock is harvested for use in the aquarium trade from collections in the wild near reefs, where parts may become detached from the main body of coral by storms. Or it may be from small coralline rocks which are "seeded" by an aquaculturalist in warm ocean water, to be harvested later. Live rock can also be seeded by adding base rock to an active reef aquarium that already has live rock. Live rock harbors a wide variety of corals, algae, sponges, and other invertebrates, when they are collected. Corals added later will often be attached to live rocks.

There are different types of live rock. In J. Charles Delbeek's article "Your First Reef Aquarium", published in Aquarium USA in 1994, under the Live Rock section he refers to "reef rock" basically as pieces of coral or coral rock from outside the reef that have broken off and fallen to the bottom that then becomes covered with encrusting organisms, such as coraline algae and sponges. "Inshore rock" Delbeek refers to as rock from inside the reef that has a tendency to be more dense and becomes covered with macroalgae, clams, mussels, crabs, shrimps, and other unwanted organisms. In Delbeek's view, this more pourous reef rock is preferable to the more dense inshore rock because it cycles an aquarium more quickly.

Explaining the purpose of live rock in an aquarium, Delbeek: "The use of live rock immediately introduces into the aquarium numerous algae, bacteria and small invertebrates all of which contribute to the overall quality of the aquarium water. Live rock has just as much, if not more, surface area for bacteria than a trickle filter. Since live rock in the aquarium contains various types of bacteria, algae and corals, waste products such as ammonia, nitrate and phosphate can have a number of fates. Ammonia, nitrate and phosphate are readily assimilated by algae and photosynthetic corals growing on and in the rock. Ammonia can also be quickly converted into nitrate by the bacteria on and in the rock. This nitrate can be either absorbed by the algae and corals, or it can be denitrified by bacteria in close proximity to the nitrate producing bacteria." 

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