My tank is a 75g reef with lots of live rock, live sand, and a few fish. The water quality is generally constant and very good, although my nitrates never seem to get lower than about 2mg/l. My problem is that I recently noticed that my feather duster worm seems to have shrunken – in fact it is now noticeably smaller than when I bought it. When I bought the worm, it was probably about 3" in diameter, but has shrunken down to about half that size (1.5"). It seemed to be doing fine for quite a while (8 or 9 months) in my tank, but about 2-3 months ago, I upgraded my skimmer from a crummy single pass co-current skimmer to a downdraft. The worm seems to have shrunken since that time, and I was wondering what to do about it. The worm is almost a year old now, and I don’t want to lose it. I also have a variety of other feather dusters in the tank (including some Cluster Dusters and Christmas Tree Worms), and am worried that they might be affected as well. What could cause my worm to shrink like that?
Thanks for your help!
Let me start by saying a little about worms in general. “Feather duster” is a common name that means different things to different people. Some pet shops use the term to refer to any worms that have a tube and a feeding crown, while others use it to specifically refer to only one or a couple of families of polychaetes (either the sabellid and/or serpulid polychaetes). I need to back up a step here, though. Polychaetes are one of three Classes of worms in the Phylum Annelida (the ring worms), the others being the Class Oligochaeta (the earthworms) and the Class Hirudinida (the leeches). Polychaetes are often referred to collectively as "bristleworms" although I really dislike that term, because there are so many negative connotations associated with it among reef aquarists, and because it is used in so many ways by different people that it is virtually impossible to have a useful conversation using this word. For example, some people use the term "bristleworm" synonymously with polychaete to refer to the group as a whole, others use “bristleworm” only to denote those families with particularly long bristles (such as the Families Nereidae and Amphinomidae), while others use it to refer only to the group specifically known as “fireworms” ( the Amphinomidae). Unless you know in which way the term “bristleworm” is meant, it could refer to the 10,000 currently described species of polychaetes, it could refer to a couple of specific Families of this class, or it could refer to a handful of potentially dangerous species of worms that give the entire group a bad reputation, respectively. Like the term “bristleworm,” “feather duster” can have widely varying meanings, and it is hard to give you specific answers based on my guess to which animal you are referring, but I’ll try.
You don’t mention the type of tube it lives in, which is an important detail in guessing which species you are most likely to have in your tank. I will assume that your worm is one of the more common species sold in pet shops, and based simply on the size I will guess that the tube is a soft, parchment-like tube and that the worm is likely to be a species of Sabellestarte (often called Hawaiian, Magnificent, or Giant Feather Dusters in the pet shops), possibly S. sanctijosephi from Hawaii or S. magnifica from the Caribbean. Of course without an accurate identification, it is hard to give you an exact diet suggestion for your worm, especially because some species feed almost exclusively on phytoplankton, some prefer small zooplankton, some feed on resuspended organic particles from the sea floor, some on "marine snow" and others actually specialize on decaying kelp detritus, for example. There are plenty of variations on these examples, but you probably get the idea from this brief list.
There are many different groups of suspension feeding worms that make tubes in which they live, including sabellids, serpulids, spirorbids, sabellariids, chaetopterids, etc., so like the terms above, “tube worm” does not really mean anything other than the worm being described lives in a tube. Despite the variety of species and groups included in this broad category, many of these animals have fairly similar feeding preferences and requirements. Most small tube worms feed actively on phytoplankton, but unlike some of the suspension-feeding corals I’ve discussed recently, feather dusters generate their own flow to capture food particles rather than relying primarily on the flow of currents to bring food particles to them. These worms extend their feeding pinnules (the "crown" of the feather duster) and actively pump water through the ciliated tentacles to capture organic particles as they pass through the crown (cilia are tiny hair-like extensions on the surface of cells that are under active control and used to generate currents to move water or mucus around).
Most people who keep tube worms generally try to target feed these animals to ensure that they get enough food in the aquarium, but most people are rather shocked to discover that the current is generated from the outside of the tentacles as water is drawn upwards into the crown from underneath and expelled towards the center of the ring on the upper side. This is particularly important, because most people who try to target feed these animals have a difficult enough time because the worms withdraw into the tube as soon as they sense the current generated by spraying food towards them. But if you are directing the food towards the center of the crown, even those worms that don't retract will get little to no food from your well-intentioned efforts because the food will be blown away from the animal by it’s feeding current (the center of the crown is where their waste water gets pumped away -- by target feeding the center of the crown, you're effectively trying to feed their butts). Therefore, if you are trying to feed a feather duster worm, you should be directing the food to the side and below the crown, where it will be drawn through the feeding tentacles and feed the worm. By creating water flow through the feeding tentacles, the worms actually use the eddies generated by having a branch of their crown in the flow (similar to a rock in a stream causes a swirling eddy which pulls objects in behind the rock) to cause food particles to swirl around that branch and get captured on the upper surface of the tentacle.
Depending on the species of worm and how big it is, the "mesh size" through the feeding pinnules can be very tiny or quite large, and the efficiency of capturing particles of various sizes depends on how big that "mesh" of feeding tentacles is. Tube worms are 'very' efficient at capturing particles of the correct size, and an undisturbed worm feeding at it's maximum rate can actually clear 100% of the particles of correct size (whether that is phytoplankton or zooplankton depends on the size of the worm) suspended in the water pumped through the pinnules. Again this is important, because that filtering efficiency is much higher than that of corals, clams and other animals that can also feed on suspended plankton, so, in general, tube worms should be the last to show signs of starvation -- if you have other filter-feeders, the chances are that they are suffering at least as much as your worm...
As I said above, most small tube worms feed on phytoplankton, but the very large species, such as Sabellestarte spp., tend to switch to consuming largely zooplankton as they grow – small animals feed primarily on small phytoplankton, but as the animal grows, so does the size of the mesh, and therefore the size of the phytoplankton preferred, and by the time the animal is an adult, these worms feed primarily on tiny zooplankton (rotifers, invertebrate larvae, copepods, etc.) but probably still capture large phytoplankton as well. The worms usually get enough suspended detritus and bacterial aggregates to grow when they are small, but as the animals mature and require larger plankton, the supply in most aquaria is quite limited, and specific feeding becomes ever more important. This is why many people observe that a worm initially does well in their tank, but as it grows it seems to languish and eventually suffer in the aquarium after long periods of apparently thriving. Feeding a variety of phytoplankton to small worms will obviously benefit them, but as they grows, the more zooplankton these animals will want in their diet, and the inclusion of rotifers will certainly be a good idea.
For those people who cannot obtain or culture rotifers (again this is the subject of another article for another time), there are a variety of artificial plankton products now available to feed to animals which require these sorts of tiny prey. The disadvantage of feeding prepared artificial plankton foods is that they usually settle out of suspension rather quickly, and are therefore easy to overfeed and contribute to a decline of water quality. Furthermore, few of them give exact nutritional profiles, so it is hard to determine how closely they approximate the nutritional composition of the plankton they are supposed to replace. Even so, however, they are certainly better than starving the animals completely, and if you have no other options, by all means try a powdered plankton food.