Live rock is naturally formed when natural processes place together substrate (i.e. rock) and seawater.

There are many natural processes that carry substrate into the ocean, like erosion mediated by glaciers and rivers. The ocean itself can create substrate by eroding coastlines and bedrock... and volcanic activity can also form substrate inside the ocean. However, most of the wild Live Rock used in the aquarium trade industry is formed by one natural process: coral erosion.

Here we explain how it works...

Panel 1. Tropical stony corals suck up calcium  dissolved in the water and precipitate it on their skeletons. Over time corals grow into reef structures... as new branches grow, some old branches die... and when they die they quickly get covered by algae and other encrusting organisms. In the figure, we represented live corals with an orange color and the encrusted skeletons of dead corals are in purple. As you can in see Panel 1 and on the photo below, coral reefs are a combination of live and dead coral. In recent years, however, humans impacts like coastal pollution, global warming and ocean acidification, have increase the mortality of corals. Therefore most coral reefs in the world are formed mainly by dead corals and little by live ones (like in the photo below).

Panel 2. When there is a storm and large waves, pieces of live coral and dead encrusted skeletons break off the main structure and end up as rubble on the sea floor beside the main structure.

Panel 3. It is important to point out that the dead skeletons are more brittle than the live coral... so when the storm arrive, it is mostly dead coral that ends up in the rubble pile.

Panel 4. The rubble pile is substrate that gets further colonized by encrusting organisms and coelobites (cavity dwellers). These organisms play a fundamental role in the consolidation of the reef framework. In simpler terms... sponges, algae and other encrusting organisms GLUE together rubble into Live Rock.

Panel 5. As the cycle of storms and rubble consolidation goes around... the reef grows by accumulating Live Rock in the periphery. Also, Live Rock is an excellent substrate for coral larvae to settle... so new tiny corals grow on the Live Rock. When the tine corals grow bigger they themselves will form part of the main reef structure. The cycle that forms Live rock (storm - rubble consolidation) is the same cycle that forms reefs. Given the appropriate water quality... you can start with a small pile of rubble and a few coral settlers... and end up with the Australian Great Barrier Reef!

Photo of a reef head formed largely by dead coral skeletons encrusted with coralline algae, and a few pieces or living coral.

Photograph of Live Rock taken apart into its rubble pieces. The original Live Rock was held together mainly by sponges and coralline algae.