Polychaete worms are a major food source for a number of reef fish. For example, in Madagascar polychaete worms are the third most important prey for fish, and on Virgin Island reefs at least 62 fish representing 24 families feed on them. Off Hawaii and French Polynesia, polychaetes are an important food source for certain butterflyfishes. In the Caribbean they are the dominant prey of the banded butterflyfish (Chaetodon striatus), Atlantic longnose butterflyfish (Prognathodes aculeatus), French grunt (Haemulon flavolineatum), yellow goatfish (Mulloidichthys martinicus), clown wrasse (Halichoeres maculipinna) and smooth trunkfish (Lactophrys triqueter).
Reef fish handle polychaetes in several different ways. Butterflyfishes, for example, are adept at nipping the feeding tentacles off of fan or feather duster (family Sabellidae), Christmas tree (Spirobranchus gigantea) and spaghetti (family Terebellidae) worms. Spadefishes and certain damselfishes, wrasses, the Moorish Idol, trunkfishes, triggerfishes, filefishes and tobies will also feed on worm feeding structures. Other fish feed on whole worms, which they dig out of the sand or consume at night when the worms emerge from their holes in the reef. Grunts and wrasses hunt hidden worms during the day, while squirrelfishes and cardinalfishes are nocturnal worm-eaters. Some fish, like the violet soldierfish (Myripristis violacea), will pull entire sabellid worms from their sedimentary tubes in the sand. The threadfin butterflyfish (C. auriga) feeds heavily on worms that hide in the reef rubble and takes advantage of the feeding activities of other fish to find them. This butterfly commonly follows feeding goatfish, which flip rubble over to uncover food.
Fireworms are one type of undesirable worm that often is introduced to our aquariums with live rock. They are named fireworms because of the sharp hairs along the sides of their bodies that can cause skin irritation. These worms, especially larger specimens, will eat the soft tissues of corals, anemones and tubeworms, and their population densities may explode. Thus, aquarists are often looking for ways to rid them from their aquariums. There are some fish that eat fireworms that can be employed to help control their numbers. For example, there are several species of dottybacks that seem to relish small fireworms. These include the neon dottyback (Pseudochromis aldabraensis), Springer’s dottyback (P. springeri), the sunrise dottyback (P. flavivertex) and, to a lesser degree, the magenta dottyback (P. porphyreus). Do not be surprised if you see one of these fish with the setae (the bristlelike hairs) of these worms embedded in their jaws; that’s the price they pay for eating these porcupines of the worm world. There are also a number of wrasses that will eat small to medium-sized fireworms. These include members of the genera Coris, Halichoeres, Thalassoma and Maori (Cheilinus and Oxycheilinus spp.) and bird wrasses (Gomphosus spp.). I have also seen small bristleworms fall prey to hawkfishes, sleeper gobies (Valenciennea spp.), dragonets (Synchiropus spp.) and sand perches. Other fish that are likely to eat fireworms include grunts, goatfishes and tilefishes of the Malacanthus genus.
Christmas tree worms and fanworms are often found on live rock, or can be purchased as individual specimens or in colonies. Some of these worms have a hard calcareous tube (serpulid worms), while others form their tubes out of soft sediment (sabellid worms). These worms feed and respire by folding out featherlike tentacles. Cilia on the tentacles direct food particles and water down central channels that lead to the mouth. When the worms are threatened, they quickly retract their feeding structure back in their tubes.
Unfortunately, for fan worm fanciers, some fish that are introduced to reef tanks irritate or feed on these invertebrates. For example, copperbanded (Chelmon rostrata), yellow longnose butterflyfish (Forcipiger flavissimus), the Atlantic longnose butterflyfish (Chaetodon aculeatus) and tobies (Canthigaster spp.) will bite the feeding tentacles off before they can be withdrawn. Flame hawkfish (Neocirrhites armatus) and large anemonefishes have been observed to grip the tentacles and rip the worms right out of their homes, while smaller sabellid worms are often eaten whole by goatfishes, grunts, angelfishes and surgeonfishes.
Some fishes, like the pygmy angelfishes, do not actually feed on serpulid worms but nip at the extended feeding tentacles, causing the worms to retract into their tubes. If these attacks persist, the worms will stop feeding all together. In the case of sabellid worms, herbivores will sometimes chew right through their soft tubes as they feed on diatoms that grow on them.