Hello, Sam here. Most saltwater aquarists know what a bristle worm is, but they may not know that it has function in the reef. There are many different species of bristle worm, some are scavengers and some are carnivores. Most of the small bristle worms found in a reef tank under the live rock or crawling across the sand are Eurythoe sp. These worms are scavengers and help you by eating leftover food that settles to the substrate from daily feedings or waste from the other fish in the tank. The problem occurs when their population in the aquarium grows and you’re suddenly faced with bristleworms everywhere! They may not be the most attractive things to look at, and clusters of them on rock and in substrate can be a little unsettling when you peer into your tank.
Small bristleworms in controlled numbers can actually be good for a well-established reef. They help tp keep the substrate aerated, and they are able to feed on debris that may be missed during regular maintenance. Population explosions can occur if you feed too much or too often, and if the tank is not maintained properly ensuring that most of the excess debris are not removed from the substrate. The key is to maintain a balance in thier numbers, otherwise that can create problems for your tank.
If you start to see an abundance of these little creepers in your tank there are several solutions to reducing their numbers, even if it is just for your own piece of mind. The first step is to adjust your feeding and cleaning habits. Watch the amounts and frequence of feedings to make sure that little or no food is left to fall to the floor or into the rockwork of your tank. If the worms are still really small, you can siphon portions of your substrate to remove them and excess waste, while you’re doing small water changes. If your tank has little open space to siphon, set a bristleworm trap to lure them in with bait and easy removal.
Once the population appears to be in more manageable numbers, you may want to consider introducing a natural predator. Certain fish and crabs will eat these bristle worms, helping to keep the population low. Most fish from the genus Pseudochromis or Dottybacks will eat these worms with much vigor, and many of them are colorful and attractive with a max size of just a couple of inches. The Six-Line Wrasse has been a recommended bristleworm hunter for decades, and many of the fish in its genus will also eat bristle worms. Another stand-by, the arrow crab, does a great job of reaching deep into rocks with its long arms and picking at the bristle worms.
Bristle worms can grow to a large size, some obtaining a size larger than 4 inches, and some species much larger! If the worms in your tank are larger, smaller fish or crabs will not be able to eat it. These bristle worms will need to be extracted by forceps (touching a bristle worms can be a painful idea, be sure to wear gloves to protect you from the bristles) or by using a trap.
Until next time,