What Is “Live Rock”?

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The one indispensable part of a SHOWLR system is the foundation of live rock.  The live rock is the living, breathing, heart and soul of the system, which provides the bulk of the biological filtration as well as some denitrification ability and shelter and habitat for countless critters and microfauna.  The porous interior of the rock supports large populations of the beneficial oxygen-loving Nitrosomonas and Nitrobacter bacteria that breakdown deadly ammonia and nitrite into less toxic substances (primarily nitrate).  Deeper inside the live rock, where oxygen levels are nil, anaerobic denitrifying bacteria take hold and complete the nitrogen cycle, breaking down nitrate into harmless nitrogen.  This helps keep the nitrate levels in the seahorse tank low.  As a result, live rock is superior to most other forms of biofiltration, which lack this final anaerobic step and cannot carry out denitrification.  This makes live rock doubly good at maintaining optimum water quality.

Equally important, the rockwork provides cover for the seahorses.  By this, I mean the rock allows the seahorses to hide and conceal themselves completely whenever they feel the need.  Seahorses are shy, secretive creatures that rely on camouflage as their primary means of protection, and if they feel too exposed and vulnerable, it can be stressful for them.

Despite its beauty, natural appearance and the many benefits it provides, some hobbyists avoid live rock like the plague for fear that they may introduce harmful pests to their aquarium along with the live rock.  This is a valid concern since potentially harmful hitchhikers like mantis shrimp, fireworms, aggressive crabs, hydroids and Aiptasia rock anemones are very often unseen and unwanted tenants of live rock.  They insinuate themselves throughout the live rock in nooks and crannies, and multitudes of these squatters may have taken up housekeeping in a good-sized piece of rock unbeknownst to the unsuspecting aquarist.  They conceal themselves within the labyrinth of rock and often escape even the closest scrutiny undetected.

But with a little care this is one time when aquarists can have their cake and eat it too.  There are a number of ways to take advantage of all the benefits live rock provides without risking unleashing an epidemic of tenacious rock anemones or turning Jack-the-Ripper loose in your tank reincarnated in the form of a thumb-splitting Stomatopod.

For instance, some seahorse keepers treat live rock with fenbendazole for a period of 3-4 days to eradicate such pest before placing it in the aquarium. Fenbendazole is an anthelmintic agent used for deworming large animals such as horses (Abbott, 2003), and 1/8 teaspoon of granular fenbendazole per every 10 gallons of water will indeed kill worms, including bristleworms, as well as hydroids, anemones and certain other Cnidarians (Liisa Coit, pers. com.). It will not harm your biofilter, most macroalgae, copepods or most types of shrimps and other crustaceans, or most kinds of snails (Liisa Coit, pers. com.), so it leaves most of the desirable life on the rock intact.  Be sure to check the water for ammonia and nitrite if you use fenbendazole for pest control this way, since the sudden die off of worms and Aiptasia anemones is likely to cause ammonia and/or nitrite spikes that must be controlled with water changes.

By and large, bristleworms are beneficial scavengers and sand sifters unless their numbers get out of hand, so a better option for many seahorse keepers is to keep the Aiptasia and bristleworm population in check using some means of biological control. Peppermint Shrimp (Lysmata wurdemanni) love to dine on Aiptasia rock anemones and several of these attractive shrimp will do a fine job of eradicating them from the aquarium.  Certain nudibranchs (Berghia sp.) also feed on Aiptasia.  Likewise, small Arrow Crabs (Stenorhynchus sp.) will keep the bristleworm population at a manageable number.  Any mantis shrimp or aggressive crabs that happen to slip by are generally fairly easy to trap and remove, and commercially made traps are available for that very purpose.

Treating the live rock with a hypersaline dip is another excellent technique for ridding it of unwanted pests.  This method doesn't kill the critters outright but merely drives them out of the rockwork so you can selectively cull through them.  Another advantage of this method is that leaves all the desirable life on the rocks intact and unharmed.

To use this technique, simply place your newly arrived live rock in an inert container filled with saltwater at a specific gravity of 1.035 to 1.040 for one minute before you cure it.  Invertebrates cannot tolerate rapid changes in salinity, so all the mobile inverts in the rock will immediately abandon there hidey-holes and bale out of the rock like rats deserting a sinking ship.  After a full minute in this extra-salty bath, the evacuation will be complete, and you can remove the now pest-free live rock and sort your catch.  Cull the invertebrates left behind in dipping container, discarding the pests you don't want while retrieving any of the refugees you might like to add to your system. One full minute in the hypersalinity is enough to drive out all the active invertebrates such as mantis shrimp (Stomatopods), crabs, and assorted worms of every description, yet this brief period of immersion will not harm encrusting organisms or sessile life.

Cautious aquarists who want to make doubly sure that their live rock is free of unwanted hitchhikers can follow the hypersaline bath with a regimen of fenbendazole.  The hypersalinity will drive out the mobile pests while the fenbendazole will eradicate any remaining sessile invertebrates that could be harmful, such as anemones, hydroids and other Cnidarians.  The one-two punch of hyposalinity plus fenbendazole produces pest-free rock.  Caution: Do not use fenbenazole in a reef tank or on live rocks intended for use in a reef tank!  It will kill off many polyps and corals and inverts besides Aptasia or hydrozoans!