Pests In The Aquariium

Not open for further replies.


Reef enthusiast
Anyone that enjoys gardening knows, as the garden gets better and better, the likelihood that pests will appear and upset everything increases. The same is true in a reef tank. As our level of success has increased to the point where we now can keep just about anything and even have it reproduce, there is an increased incidence of marine pests suddenly appearing and causing havoc in our tanks. Many of these pests were probably in the tank before, but since we had difficulty keeping most animals alive for the long term, we most likely never noticed them. However, now that we can keep animals alive and thriving in our tanks for years, these pests are becoming more problematic. Fortunately, with this increased knowledge about pests, we are gaining an increased understanding of how to eliminate them. Even more encouraging is that in many cases we are able to eliminate these pests naturally.

Many pests arrive on the live rock or within the coral colonies themselves. One of the most frequently encountered of these pests is flatworms. These animals consume zooanxthellae as well as the coral's tissue. They are usually small and can only be detected by following the thin thread of dead tissue in the coral colony. The damage caused by the flatworms may not kill the colony directly, but may lead to a site for secondary infection. The best and easiest way to rid a tank of these pests is to introduce a mandarin fish which rapidly consume these pests as well other micro fauna in the tank.

Similar pests that may come in on live rock or that we may introduce ourselves are the nudibranchs. Most of these animals possess vibrant colors and interesting patterns so we can't help but consider them as worthy additions to our miniature reef community. In addition some of these animals possess the ability to mimic the coral upon which they feed. The nudibranch that feeds on Xenia and mimics its polyps is one that immediately comes to mind. However, their beautiful colors are only an indication of the poisonous nature. This poison, that is an integral part of the nudibranch's makeup, is derived from its food source of nematocysts. These nematocysts are the defense cells of many types of invertebrates including corals, anemones, jellyfish, etc.

Each species of nudibranch has a specific food source from which it derives these nematocysts. Therefore the addition of a single or small number of the same species of nudibranchs is not likely to decimate the entire invertebrate community. However, if these animals do find a coral to their liking it is very likely that the entire coral colony will be consumed if steps are not taken to remove the nudibranchs from the colony. Due to their poisonous nature these animals have few enemies and therefore will feed both during the day and at night. As a result they are relatively easy to see and attempt to remove.

There is also a new type of nudibranch that has recently become a pest because only now are we keeping some of its favorite food items. This nudibranch feeds exclusively on corals of the genus Montipora and more specifically Montipora capricornis. These relatively tiny nudibranchs are less that ¼ inch in size and look like the Berghia nudibranchs that have been used to eradicate Aiptasia anemones. These nudibranchs start feeding on the bottom of the capricornis colony, and once they have removed all of the tissue from the underside of the colony they will start to remove tissue from the upper more colorful regions. At this point the number of nudibranchs can be quite large.

Thanks to efforts by Leroy Headlee we have found that the only way to eradicate these pests is to soak the colony in freshwater for 30-45 seconds. This will cause the nudibranchs to burst apart and die. Do not soak for longer than necessary as this will kill the colony, and make sure that the water is matched for temperature and pH. The soaking then needs to be repeated at 10 days to kill any eggs that may hatch. This method has helped saved numerous capricornis colonies in my tank even when they were reduced to tiny colonies. I have however, found this freshwater treatment to be stressful to some colonies so before I try it I attempt to wash the nudibranchs off of the Montipora by removing it from the tank at night and then shaking it vigorously in a saltwater bath to dislodge the nudibranchs. This method can work even better if, after shaking in salt water the colony is inspected thoroughly with a flashlight and any nudibranchs that are left are removed with tweezers. Larger nudibranchs can be removed by siphoning them out of the coral head with a large diameter hose when they are not firmly attached to the substrate. When siphoning them out, siphon them to a separate container rather than into the sump to avoid any possibility of them poisoning the tank.

Unlike the nudibranchs which frequently show themselves due to their bright colors this next group of animals are extremely secretive and if they are seen it is generally as a streak of motion. For those of you with reef aquariums you know immediately that I am talking about mantis shrimp. While these animals are at least as interesting and colorful as the nudibranchs, they are much farther up on the scale of destructive animals that are very difficult to remove. These shrimps received their name because of their resemblance to a praying mantis. Like this insect, mantis shrimp possess lightning fast claws that they use for capturing food and defending themselves from enemies. Mantis shrimp possess keen vision from eyes that are placed on stalks which allow them to see around corners and from out of their burrows. In addition they are also sensitive to even the slightest vibration, so that if you are near the aquarium they can usually feel your presence and remain in their hole. Therefore rather than seeing them to know they are present, one needs to either listen for them or look for signs of their presence.

The very mechanism that makes them a formidable enemy, their powerful claws, also gives the mantis shrimp away. If some unknown source of clicking is occurring in your tank it is a good bet that a mantis shrimp is present. If the sound is a single loud click it probably is not a mantis shrimp, but most likely a pistol shrimp, which for the most part is harmless. If it is a mantis shrimp that is clicking, these are generally the less harmful of the shrimp as their diet consists primarily of mollusks. A better indicator of a mantis shrimp's presence is the disappearance of numerous small fish over time without a trace.

There are two types of mantis shrimp encountered: spearers and smashers. These names are descriptive of how the animal obtains its food. he spearer has exceedingly sharp claws that it moves very rapidly to spear or slice its prey or to defend itself. I have personally had this type of shrimp split my thumb open from top to first knuckle with a single flick of its claws. Therefore, handling them should be avoided even when trying to remove them. The smashers also move their claws in rapid fashion; however they move them in order to stun their prey. The movement is more ballistic in nature. These shrimp use their claws to crack open mollusks as well as to stun fish that get close enough.

In either case it is best to try and remove these pests as soon as possible. Unfortunately this is much more easily said than done. have found these animals to be one of the most cunning inhabitants of the reef. I have only been able to remove them by luck inspired ways. I either waited until I saw one enter a rock, then removed the rock or I trapped them in a fish trap in which I slowed the animal down by using bait wrapped in nylon stocking. There is no easy way to rid the tank of these pests, other than the previous methods as well as quarantine, which is discussed below.

The mantis shrimp is not the only crustacean that can cause damage within a reef tank. Several other crustaceans, especially crabs can cause at least as much damage. These harmful crabs should not be confused with the small little crabs of the genus Trapezius that inhabit many of the stony corals. The first of these are the Xenia crabs. These crabs only eat Xenia and consequently they are only infrequently encountered. However when they are present they very rapidly destroy a Xenia colony. These crabs match the color of the Xenia on which they feed and therefore they may not be detected until too late. These crabs generally are found in pairs, and the best time to find them is at night when they will appear as bumps on closed heads of Xenia. The best way I have found to remove them is to lift out the Xenia colony on which they are located and very gently push the crabs with tweezers or forceps off of the Xenia colony without damaging the colony.

Mike Paletta is the author of The New Marine Aquarium and Ultimate Marine Aquariums. He has been in the hobby for over 15 years and has written numerous articles for Aquarium Fish Magazine, Tropical Fish Hobbyist and Aquarium Frontiers.
(part-2 Cont)

Unlike the Xenia crabs which are specialized feeders and easily removed, the Hairy crabs are generalized feeders and are very difficult to remove. These crabs will eat and destroy anything that they can get a hold of including leather corals, hard corals, mollusks, tube worms, and anemones. These crabs only come out at night and are very difficult to remove. These crabs can also get very large and are therefore potentially extremely dangerous in terms of the havoc they can wreak on the inhabitants of reef aquarium. In this crab group there is a specific group of crabs that feed on the polyps of SPS corals. These crabs are easy to spot as they have very bright blue eyes. These crabs usually come in pairs so it is necessary to remove both of the animals in order to limit their destruction of coral heads. The best way to limit the destructiveness of these crabs, as previously noted, is to prevent these crabs from entering in the first place. Since this is not always practical, there are at least two other methods for their removal. The first method may seem rather cruel, but it is necessary. A piece of bait, i.e. shrimp or squid, is placed near the crab's known residence. This is best done right before the lights go out. A red lamp is then placed near the tank so that the bait can be viewed. If you are fortunate, soon after the lights go out the crab will approach the bait. At this time the crab can be smashed with a piece of PVC pipe and removed from the tank. This method requires patience as it may take more than one night, and also quick reflexes as the crab moves surprisingly fast. The second method I have tried is to use a wide mouthed glass jar as a trap. I place the jar on at a slight angle near the crab's home and place the bait in the bottom of the jar. Once again I do this right before the lights go out. If I am lucky, the crab will smell the bait and enter the jar. However, due to the smooth sides and angle of the bottle, once the crab enters the jar he will be unable to crawl back out and he can be removed in the morning. The only problem with this method is that it will usually only work when the crab is hungry enough to overcome his fear and enter the bottle. Otherwise what usually is caught in the jar are fish and the tank's desired shrimp inhabitants.

Another group of well-known enemies of the invertebrate aquarium are members of the bristle or fire worm families. These worms frequently sneak in as unwelcome stowaways on pieces of live rock and under pieces of coral. These worms eat virtually any sedentary invertebrate, but are particularly fond of Euphyllia and soft corals of all types. I have found that there are two types of these worms present in the reef aquarium, and they can be characterized in terms of what area of the reef tank they inhabit as well as their size. The smaller and less dangerous of these worms live in the substrate, where they multiply rapidly to high levels. These worms generally only reach a length of from two to three inches. Due to their small size, these worms generally don't pose that much of a threat to the overall invertebrate population. They also are very good at keeping the substrate aerated, so they should not be removed. However they can devastate individual colonies of animals as well as individual specimens, especially those which are located on or near the bottom substrate and that are already damaged. Generally these worms will not attack healthy specimens, but should an animal start to deteriorate they can rapidly consume it.

The other type of bristle worm is larger and far more dangerous and generally lives in the live rock itself. The two largest of these types of worms are members of either the Nereis or Eunice species which can reach lengths of from 6 to 16 inches.

Night is generally the only time these animals come out of their hideouts, and this is only to feed. Consequently it is very difficult to try and catch them for removal, as it is necessary to wait until they are hungry enough to venture out of their holes. At this time it is possible to try and remove them through various means. One way to accomplish this is by pulling them out using hooked tweezers; however, they frequently break apart during this procedure and the portion that remain in the rock will grow back into a full size specimen. Also these animals sense even the slightest vibration, so if you bump the tank in any way they will quickly pull back into the rock. It is really quite amazing how fast they can completely pull back into the rock and out of harm's way. The best way to remove them is through the use of a natural predator. The best of these is the Harlequin Tuskfish which will consume even the largest bristleworm without any damage to itself. For smaller worm problems a green bird wrasse is a good choice.

Another group of troublesome inhabitants that are encountered in reef tanks are predatory mollusks. These include cowries, whelks, volutes, cone shells, and some snails. For the most part, these animals resemble nothing more than the typical snails that one frequently encounters. However, unlike the benign and generally useful herbivores that we may deliberately introduce, these animals are aggressive carnivores that attack all variety of invertebrates from Actinodiscus to Zooanthids. While resembling common snails they are different in terms of their feeding mechanism. The most dangerous of these animals possess a venomous radula that is used for injecting a rapid acting poison into their prey. In addition, in some species the radula has developed into a drill which is used to bore through the shells of the desired prey.

For the most part, these animals are specialized in terms of which type of animal they prefer to feed on. This does not however make them any less of a threat to our charges. One of the most interesting of these parasites is the Rapa rapa snail. This snail is extremely specialized in that it is a boring snail that eats only Sarcophytons and Lobophytons (leather corals) and Sinularias (finger leather corals). It is a very difficult pest to detect, in that it bores to the center of the leather coral's stalk while it is small and then continues to eat the entire inside of the animal. I have had them in my tank twice and in each instance I can only assume that they arrived already inside the leather coral that I purchased. The only way that I knew they were present is that the leather coral started showing signs of stress as indicated by the stalk turning yellow and the polyps not expanding. On close examination of the coral, I found what looked like a small incision on the stalk where the coral had healed over. When I pushed on this incision the stalk broke apart revealing the snail doing his damage inside the stalk. When he was removed the coral regained its health in a couple of weeks.

Part-2 (cont)

Unlike the Rapa rapa snail however, most of these other Mollusks mentioned are easy to spot and easily removed. They usually come out at night and due to their slow nature can be quickly picked out. However, care should be taken during their removal to avoid being stung by their poisonous radula. To remove them I usually use a large pair of tweezers, just to be on the safe side.

Another parasitic mollusk is the pyramidellae snails. These snails resemble grains of rice and they feed on Tridacna clams. These snails enter the clam via the bysus opening and stress the clam to the point of death. The best way to eradicate these snails is to use six-lined wrasses or Pseudochromis springeri to eat the snails.

Another member of these small coral predators is an animal that has only recently been discovered to be a parasite. This little starfish can inflict as much damage in a closed system as a crown-of-thorns can do on a reef. This starfish remains relatively small and usually never grows to more than ¾ of an inch across. This small size allows it to hide within the coral colony, only to come out at night to feed on the polyps. The starfish ranges in color from beige to gray to even mottled red, which allows it to hide within the coral colony. What differentiates it from most starfish is that it has seven legs and the legs are all of different sizes. This starfish feeds on just about any type of coral including LPS corals like Euphyllia and Lobophyllia, soft corals, and virtually all SPS corals. In this last group, these starfish seem to prefer Stylophora and Seriatopora although when these corals are not available they will also consume Acropora and even Blastomussa.

These starfish reproduce rapidly and can quickly overrun a tank and damage many corals unless steps are taken to control and reduce their numbers. Since they feed at night, scouring the tank carefully at night and plucking the starfish from their food is one way to reduce them. However, unless this is done routinely these animals may quickly become a problem again. For this reason, a natural predator like Harlequin shrimp may need to be employed to completely eradicate them. Unfortunately, the reason that these starfish may now be a problem is that the removal of Harlequin shrimp from the wild has become increasingly more difficult. These starfish seem to come in on live rocks and coral colonies from all over, but more of them seem to be coming in from Fiji than anywhere else. For this reason, it may now be necessary to quarantine live rock and corals before introducing them into the display tank. Do not think that these starfish cannot wreck havoc because of their small size. A single starfish can completely consume a medium Acropora or Euphyllia in only a few days.

While the previous nuisances occur from time to time, one nuisance occurs in virtually every reef tank: Aiptasia anemones. These pests reproduce rapidly and burn everything they touch. The best way to remove them is to use a natural predator, injections and compounds are just not that effective. The absolute best of these is the Black-banded butterfly (Chaetodon striatus). These fish will remove virtually every remnant of these pests without bothering the corals and they are very hardy. Nothing else is close to as good as these fish are at removing Aiptasia. The second best creature at removing these pests are nudibranchs of the genus Berghia. These nudibranchs work well, but requie at least 2-3 months to do their job.

A similar pest is the majano anemone. This little green anemone closely resembles a miniature bubble-tipped anemone, reproduces and burns in a fashion similar to Aiptasia. Angelfish of the genus Centropyge, Apolemichthys and Pomacanthus all consume these anemones. These fish are all somewhat fond of feeding on corals so care should be taken one for the purpose of consuming anemones.

This list on nuisances for the reef tank is just a start. It is becoming clear that a new list of pests, some of which are microscopic, are becoming problematic. Once these are classified, work will need to be done to determine how to eradicate them. So this article is just a start in outlining some of the nuisances that we face with our reef tanks.
Not open for further replies.