Rust Brown & Acropora-Eating Flatworms
There are two common types of flatworms (aka planaria) that us hobbyists are more then likely forced to face at one time or another.
Rust Brown Flatworm (Convolutriloba retrogemma)
The most commonly found flatworm, which is more of a nuisance then anything, is the Rust Brown Flatworm. Rust Brown Flatworms are tan, brown or rust colored with a red dot, and reach a size of up to 1/4" in length. They are oval and slightly elongated with two tail-like appendages at their posterior. They will reproduce rapidly in aquariums with elevated nutrient levels. Populations of these pests can increase to a point where they will actually perch on corals, blocking the light from reaching the corals' tissue, thus damaging them to the point where they will die. Some believe that the rust brown flatworms actually feed on the zooxanthellae from coral tissue, which also damages the corals to the point they will die off.
Where to spot them
From directly on your corals to on your tank glass. You can find these just about anywhere in your tank but normally in low flow areas.
Solutions
Prevention is the best way of controlling pests. If you have quarantined your corals before introducing them into your display tank; your battle with these guys is going to be much easier. In quarantine you can physically remove visible flatworms by siphoning them off (flatworms do not have a strong grip). Just be careful to not harm your more delicate corals. Also, maintaining low nutrient levels with the use of carbon and aggressive protein skimming, along with increased water flow will help to reduce the populations of these pests.
Natural Solutions (Please read up on tank compatibility and care before introducing any species into your tank)
- Blue Velvet Nudibranch (Chelidonura varians) very sensitive to changes in water chemistry and has a short life expectancy in the home aquarium.
FISH (The below wrasses consume flatworms, but most likely will not rid your tank of these pests completely)
- Six Line Wrasse (P. hexataenia)
- Halichoeres Wrasse, such as Yellow Wrasse (H. chrysus),
- Macropharyngodon Wrasse such as the numerous Leopard Wrasse (Macropharyngodon sp.)
- Dragonets such as the Spotted Mandarin (Synchiropus picturatus).
Home Remedies
- Brief freshwater bath or dip. (If trying this method please use caution to reduce the amount of stress on your coral)
With severe infestations, you may have to employ a combination of all methods mentioned above in order to eliminate or even control the populations of these pests.
Sources
http://saltwater-aquarium-advice.com/blog/?tag=pest-flatworms
Acropora-eating Flatworm
The Acropora Flatworm is a more aggressive species of flatworm that consumes the actual tissue of Acropora sp. corals at a rapid rate. This flatworm is harder to spot in your tank as it appears white to opaque in color, and is mostly oval in shape.
They seem to prefer species of Acropora that have shorter polyps, and are most commonly found on Staghorn types and Tricolor species. This flatworm is very invasive, and immediate action should be taken if noticed in your aquarium.
The Acropora-eating Flatworm can be recognized by the rapid tissue loss in certain colonies of Acropora, and their presence will be known by the gold to brown egg masses that they leave behind on the bare coral skeletons.