Pests, Nuisance Organisms and Ecological Imbalance

Live rock, sand, corals and even the water in a fish bag carry small organisms into a system: worms, snails, crabs, sponges, algae and many more. These are called hitchhikers. Choosing live rock means accepting what it brings, wanted and unwanted, and most of what it brings is harmless or useful (Module 22).

Nuisance organisms are harmless in small numbers and become a problem only when they spread: hair algae, cyanobacteria, bristleworms or small sea stars. Pests harm the animals you keep directly: they eat coral tissue, sting neighbors, smother corals or prey on snails, shrimp, clams and fish.

Identify first. Photograph anything new before you touch or remove it, note where it's and when it appears, and compare it with a reliable identification guide. A harmless worm and a pest can look alike, and the wrong response does more damage than the organism. Removing a harmless animal costs the system some of its biodiversity, and a hasty removal of a real pest can spread it.

A reef system's stability comes from biological and ecosystem balance: many kinds of bacteria, algae, grazers, predators and small animals competing for the same space and food, so that no single one can take over. Quality live rock brings much of that diversity in from the start (Module 22). Starting a system without quality live rock makes that balance very hard to reach.

In this course's experience, a reef system takes 1 to 2 years to stabilize, and along the way it goes through a series of nuisance outbreaks, one after another, as its community fills in. That's normal for a maturing system, not a sign that it has failed.

An outbreak usually follows something that opens space or removes competition: new bare rock, a die-off, a new arrival, or a change in lighting or flow. Nutrients bottoming out at zero also starve corals and favor cyanobacteria and dinoflagellates, so this course's practice keeps nitrate and phosphate measurable, with nitrate ideally no more than 30 ppm (Module 17).

Most nuisances have a predator. The lasting answer is biological: add the grazer or predator that eats the nuisance, and build the diversity that competes with it. Removing it by hand buys time while that balance builds. Nothing good happens quickly in a reef system: correct one thing at a time, record it, and give the system time to respond.

Algae enters a system on rock, sand, frags, or in the water with a new fish. Remove it as soon as you see it: a small patch is easy to clear, and a large one takes weeks.

Grazers are the control. In this course's practice, nuisance algae in general is controlled with a variety of grazers: several kinds of snails, urchins, and herbivorous fish such as tangs. Each grazer prefers different algae and different surfaces, so variety matters more than numbers. Removing algae by hand helps while the grazers catch up.

Diatoms are a powdery brown film, usually the first growth on new rock and sand. In the new-tank phase they usually die off on their own within a couple of weeks. Diatoms that keep returning after that point to a nutrient imbalance, nutrients running too low, or too little diversity in the system's microbiome, its community of bacteria and other microorganisms. A bacterial additive, a product of live bacteria, can be dosed to build that diversity.

Green hair algae grows as long strands or a short turf, most often on bare rock where little competes with it. A variety of grazers is the answer. Remove what you can by hand, taking the whole strand, because tiny fragments left behind regrow.

Bryopsis is a feathery green algae that few grazers will eat, so adding grazers won't clear it. It needs treatment with a fluconazole medication, used strictly as directed on the product. Fluconazole targets Bryopsis and Derbesia, not other hair algae. Algae killed this way releases the nutrients it held, so test nitrate and phosphate during treatment.

Bubble algae (Valonia and Ventricaria) grows as green bubbles on rock and coral bases, where it traps detritus that feeds more growth. It favors good light and low flow. Remove each bubble whole, taking the rock out if needed, and add emerald crabs (Mithraculus sculptus), which graze it. Improve flow where it grows.

Cyanobacteria, or cyano, is a photosynthetic bacterium that forms slimy sheets, usually red or purple, sometimes green or black. It starts in still areas where detritus settles and spreads upward over sand and rock. It can grow at zero nitrate and zero phosphate, so starving the system makes it worse, not better.

Correct the cause. Increase water movement into the dead spots, with an extra pump or by opening up the rockwork (Module 13). Bring nitrate and phosphate into balance, neither high nor zero (Module 17), and keep alkalinity and pH stable (Module 19).

Remove the mats. Lift mats off the surface with a turkey baster or a siphon, into a filter sock, during a water change. Take only the mat: never vacuum or dig into a reef sand bed, whose fauna keep it clean.

Chemical cyano treatments work, used strictly as directed, but cyano returns if the cause isn't corrected.

Nuisance dinoflagellates, or dinos, are single-celled organisms, neither algae nor bacteria. They form brown, stringy, snot-like mats with trapped air bubbles on sand and rock. Many reduce or vanish at night and come back when the lights turn on. They look like bubbly snot, where cyanobacteria forms a slimy sheet. Different species respond to different treatments.

Causes. In this course's experience, dinos follow nitrate and phosphate at or near zero and a bacterial community that has been stripped back. Test both. If either reads zero, raise it into a measurable range by reducing export, feeding more, or dosing nitrate or phosphate (Module 17).

Control. Remove as much of the mat as possible, as often as possible, from the surface and without digging into the sand. Dose a bacterial additive regularly, so that bacteria compete with the dinos for nutrients. UV reduces only the species that have a free-floating stage, the ones that vanish from surfaces at night, and UV also lowers the biodiversity of a diverse system (Module 21). Blocking all light for 3 to 4 days is reported to knock them back, because dinos are photosynthetic.

Aiptasia are small brown anemones with long, thin tentacles that retract into the rock when disturbed. They arrive on live rock, coral frags and plugs, sting and kill nearby corals, and spread by pedal laceration: small pieces torn from the base each grow into a new anemone. Deal with each one as soon as it appears; once there are dozens, control is hard.

Majano anemones are similar pests with short tentacles and a wider disk, often green to brown. They sting corals and multiply across rock.

Never crush, scrape or cut one in place. The pieces drift away and regrow. Cover and inject each one with a thick aiptasia paste, used as directed. Majanos can also be treated with a thick calcium hydroxide (kalkwasser) paste, which kills or injures anything it touches, so apply it only to the anemone and keep it off corals and your skin. Repeat applications are often needed. If you scrape one off, take the rock out of the system first and remove every trace of tissue.

Predators. Berghia nudibranchs (Aeolidiella stephanieae) eat only aiptasia, not majanos, and starve when the aiptasia are gone. The aiptasia-eating filefish (Acreichthys tomentosus) is among the most reliable, but it can be a risk in a reef system. Peppermint shrimp (Lysmata, most often L. boggessi) vary: some individuals eat aiptasia and others ignore it, and camel shrimp, often confused with them, aren't aiptasia eaters. Copperband butterflyfish are hit or miss. Most aiptasia predators ignore majanos.

Acropora-eating flatworms (AEFW, Amakusaplana acroporae) are a few millimeters across and colored like the coral. The first sign is usually damage: bite marks and pale or bare patches starting at the base of an Acropora colony and working upward, with egg clusters laid on the bare skeleton at the base. If you find them, move every affected colony to a separate tank, remove the egg clusters, and dip weekly for 4 to 6 weeks. Return a colony to the display only when no flatworms or eggs have been seen. Some wrasses eat them, but results vary.

Montipora-eating nudibranchs (MEN) and zoanthid-eating nudibranchs (ZEN) are small sea slugs. MEN are white, and their egg masses sit on the underside of the affected coral or on rock beside it. ZEN have gills colored like the zoanthids they eat and move around inside the zoanthid mat. Both feed at night and can strip a large colony. There's no whole-system treatment for either, so prevention matters most. In this course's practice, sixline wrasses (Pseudocheilinus hexataenia) are kept to eat Montipora-eating nudibranchs and similar pests. Remove adults by hand with forceps every night under a red light for 7 to 14 days, and remove each egg cluster you find, cutting away the piece of coral that holds it if needed.

Red bugs are tiny mite-like crustaceans with orange-red dots, found on SPS corals and usually noticed when the coral looks irritated. The preferred treatment is a dip made with a veterinary medication, which is toxic to crabs, snails and shrimp, so infected corals are treated outside the display.

Why dips miss them. A coral dip kills most adults but not the eggs, which hatch days later (Module 23). Inspect every new coral closely before and after dipping, remove egg clusters, and re-dip on a schedule during quarantine.

Sundial snails (Heliacus) have a shell that's round at the base and twists upward to a point, banded in tan and brown. They're often found within a zoanthid colony, where they puncture the polyps and feed on their tissue and fluids, leaving each polyp an empty shell. Inspect new zoanthid colonies closely and remove every snail you find by hand.

Pyramid snails (Pyramidellidae) are tiny white cone-shaped snails, a few millimeters long, that pierce the mantle of giant clams and feed on their fluids, mostly at night. By day they hide at the base of the clam or between the ridges of its shell. Move the clam to a separate container of system water, remove the snails by hand, and brush the shell with a new toothbrush to remove eggs. Some wrasses, such as the sixline wrasse and several Halichoeres species, eat them (Module 28).

Vermetid snails don't move: each lives in a tube attached to rock, coral or equipment, and looks like a tube worm. It casts a sticky mucus web to catch food, and the web stresses nearby corals, causing tissue loss and stunted growth. They can spread quickly. Break off and remove each tube with a small chisel, bone cutters or pliers, or seal its opening with a thick layer of epoxy or reef-safe super glue. Excess nutrients feed them, so keeping nutrients in range slows their spread.

Bristleworms are segmented worms that hide in rock and sand and come out at night. Nearly all are harmless scavengers that eat detritus and uneaten food, and their numbers follow the food available. If they become numerous, reduce detritus and overfeeding. Fireworms are a venomous type of bristleworm with a painful sting; one species, the bearded fireworm (Hermodice carunculata), is a coral predator. Bristles of any kind break off in skin, so handle these worms only with gloves or forceps.

Red planaria are small red or rust-brown flatworms that multiply on rock and corals where flow is low and nutrients run high. They don't eat coral, but in large numbers they block its light and can kill it. Dying flatworms release a toxin, so lower the population first: siphon them off the rock for 5 to 7 days, then use a flatworm treatment as directed, then siphon out the dead, do a large water change and run activated carbon. Improve flow and lower excess nutrients so they don't return.

Asterina stars are small sea stars that come out at night. In this course's practice, regular Asterina eat microalgae and are harmless, so they're left alone. They also regrow from broken pieces, which is one more reason not to break them up in the tank.

Mantis shrimp and predatory crabs, such as the gorilla crab, a hairy crab usually with black claws, arrive in live rock and eat snails, shrimp, crabs and even fish. Signs are snails and hermit crabs disappearing, and empty or broken shells. Clicking from the rock can be a mantis striking prey, but it's often a harmless pistol shrimp, so clicking alone proves nothing. Set a baited trap, or take out the rock it lives in and drive it out over a bucket, away from the display.

Identify it. Photograph it before any removal and confirm what it is. Crushing or tearing an organism in the tank can spread it: pest anemones and sea stars regrow from pieces, and dying flatworms release toxins.

Find why it spread. Check flow, nutrients, light and detritus, and whether its grazer or predator is missing, and look back through the records for a new arrival that skipped a dip or quarantine. An outbreak usually has more than one cause.

Use the least disruptive control first. Remove it by hand, improve the conditions that favor it, then use a targeted method: a paste on one anemone, a trap for one crab, a dip for one coral. Whole-system treatments come last, because they affect every animal in the system.

Change one thing at a time, record what you did and when, and watch the response before the next change. Prevent the next one by dipping and quarantining every new coral and invertebrate (Module 23).