Flatworms covering corals in saltwater aquariums can be a real pain, especially when they multiply to near epidemic proportions or start feasting on your favourite Acropora specimen…
Most flatworms are actually beneficial to your tanks eco-system. But, there are 2 main groups of flatworms that you do not want in your aquarium…
The first group are commonly known as the brown rust flatworms namely those from the genus Convolutriloba sp. and Waminoa sp. They are brown/rust in colour and have a red dot at one end.
Convolutriloba species Grow and live on most surfaces and Waminoa species live on corals only. Neither of these flatworms are actually predators of corals, the problem with them is that populations of these flatworms can grow exponentially and sometimes literally take over the aquarium.
Sometimes their numbers can be so many that they begin to affect the amount of light that reaches the coral, it is also recently been proved that these flatworms compete with the corals for their planktonic food. Basically, the brown rust flatworms if left to multiply to great enough numbers can starve corals to death.
The second group are the Acropora eating flatworms (unknown species), these are predators to Acropora species of corals. Unlike the brown rust flatworms they will do rapid physical damage to Acropora corals by devouring the soft tissue.
They are hard to spot because they are white and small, often they can be identified by the pattern of damage on the coral tissue (which can be easily mistaken for rapid tissue necrosis) and by golden coloured eggs laid usually at the base of the coral.
To successfully battle this pest you should quarantine infected corals immediately and remove as many adults and eggs as you can. In some circumstances it may be necessary to frag a healthy section of coral to save the entire coral.
So, how do you get rid of pest flatworms?
1. Manual removal: of adults and eggs, once again this done in quarantine with tweezers or a toothpick is the best way, putting the coral back into the display tank after it has been flatworm free for at least a few weeks. You can often also siphon the flatworms off the coral using some small diameter tubing like airline tubing a syringe can work in the same way.
2. Biological controls: the beautiful Blue Velvet Nudibranch (Chelidonura varians) is an excellent predator of flatworms, indeed the best around but this creature may starve when all the flatworms have been eradicated. The most effective fish are the 6 line Wrasse (Pseudocheilinus hexataenia), Melanarus Wrasse and Yellow Wrasse . People often recommend Dragonets, but many times this fish will have no interest in the flatworms.
3. Freshwater dip: This technique is very good at destroying the small flatworms, which “pop” from the osmotic pressure, however it can be harmful for more sensitive corals, but the harm can be minimised by dipping for a very short amount of time. If you want to do this, dip for 5-10 seconds in freshwater (chlorine free) which is the same pH and temperature as the tank water to reduce stress on the coral.
4. Preventative dip: The best method of avoiding pest flatworm outbreaks is a preventative dip in an iodine-based solution like Lugols solution before you introduce your new coral or frag to the display tank. This is the first thing any sewrious coral keeper should do when they get their coral home.
5. Chemical treatments: There are a number of chemical treatments available like Levamisole hydrochloride, sold as Levisole™ and other broad spectrum deworming agents that can effectively kill flatworms in your tank, but the problem is effects to beneficial worms. Aternatively Salifert’s Flatworm Exit™ is a widely used flatworm eradicator and has a number of good reports. The real problem with chemical treatments is pollution produced by the mass die off. Dying flatworms can release toxins into the tank that have been known to kill other marine life and you also have the problem of removing all the bodies before they decay and throw out your water quality. Using a lot of saltwater to dilute the chemical effects out after the initial treatment and siphoning up dead flatworms immediately can help a lot. Only use as a last resort and use very good chemical (activated carbon) and physical filtration as well as big water changes if you go down this path, it also greatly minimises and damage to other organisms do this in a quarantine tank if you can.
Follow these simple guidelines and unwanted flatworms will soon be a thing of the past in your reef aquarium!