Aquatic Invertebrates of Montana
Montana Chapter AFS- Tubifex Research
I am starting to feel that I need to apologize to those who have heard this before. I only have one Tubifex story and it has not changed much even with large amounts of new data. That is a good thing, but it might get old for some of you.
The biggest advance in research and eventual management of the myxosporean fish parasites was establishing the connection with the actinosporean worm parasites. It is now known for about a dozen species and highly probable for all 1200 described myxosporeans, that they represent an alternate form in the life cycle of actinosporean worm parasites. While there may well be groups of actinosporeans that do not involve fish in the life cycle (these must have evolved before fish were even present), it seems clear that using fish to mass-produce and disperse resistant spores is a very successful strategy for these parasites. It can be hard on the fish.
None of Montana's aquatic invertebrate biologists worked seriously on oligochaetes at the onset of the whirling disease problem here. I agreed to help fill this void a year and a half ago now. I thank Dick Vincent and the Montana Department of Fish, Wildlife and Parks for getting this project started and for continuing to support it. Ernie Vyse and the Department of Biology at MSU-Bozeman have also supported this project. My basic goals are to master aquatic oligochaete identification, conduct a state-wide survey of all species, emphasizing Tubifex tubifex, map their distributions, learn their life histories and basic ecology and respond to the needs of whirling disease research as they develop.
My approach, so far, has been simple- sample as many different waters as possible and then design additional samples to address the questions as they arise. My methods continue to evolve, but the goal is to get a usable sample of worms from many locations and dates onto microscope slides for identification and generate species lists with head counts for analysis. Here I am blasting the substrate with a water current generated with a hand trowel and catching the worms and lighter debris with a big net.
My field gear looks something like this. I keep it simple so that it can be used in a wide variety of conditions and easily cleaned between samples. I use the course bucket sieve and the solid bucket for field separation to get rid of course debris and heavy sediment such as sand and gravel. Failing to do so invites destruction of the specimens during transport, especially on long expeditions, which I favor. A readily available aquarium net works well with worms.
I poison the sample in the field with dilute alcohol for several minutes so that the worms lay dead like limp noodles instead wrapped up in tight coils. Preservation must be with strong fixatives such as Kahles fluid or 10% formalin. Weaker fixatives, like alcohol invites deterioration that can leave the worms unidentifiable.
Stains, such as Rose Bengal may aid sorting, but they can make identification difficult or impossible, so they are best avoided. Well preserved worms usually stand out against a black background.
So far, I have made permanent slides, because of the broad survey nature of my project. This provides long-term vouchers of every specimen. It also lets me move full speed ahead with sample processing even with unknown worms- the identifications can be completed latter. Some slides are whole worms, others are just the anterior 12 mm, which lets me get more worms on a slide. The slides are staking up- I now have over 300 samples, 2700 slides with 17,000 identified worms. This is, however, a very slow rate of specimen processing, compared to many other taxa that I work on.
If I had more time, a lot more time, I would outline some of the problems with working on worms, but suffice it to say they are about the worse ecological subjects that I have worked with in many ways. Oligochaete identification itself, is not as difficult as many believe, especially for tubificids. You do have to get used to putting every specimen under a compound scope, however. With practice, a fully mature worm in perfect condition on a perfect slide mount can be recognized to species in just a few seconds. Unfortunately, this is a lot to ask, and many specimens cannot be identified with certainty, even by experts. I examine many worms for each site to get a good species list and at least ordinal quantification.
Most of my results are available on the WWW under my World Wide Whirling Worm Web (WWWWW) page. My philosophy here is that whirling disease is such a serious, multidisciplinary problem that it requires maximum and rapid communication if solutions to be found quickly. Everything I am covering today is already on the web, there should be no surprises.
So far, I have seen about 35 species of aquatic oligochaetes from 6 families in Montana. Some 65 species seem probable here. The discovery rate is very fast compared to insects, but slower than I might expect based on worm life history. Species from at least 3 families are already known as alternate host to myxosporean fish parasites. I see no reason the others or even leeches, which I have always worked on, could not be used by these parasites.
This is the latest Tubifex map from my web site. Time will not allow me to go into details here, but some patterns seem pretty clear. I am currently preparing summaries for every drainage in the state and I hope to get more feed-back from local field workers to identify high-risk, important, unique and interesting sites to fill the gaps. On the WWW, this map, as well as more detailed maps like the Madison River drainage, are linked to a program that provides some details for the samples from any location that you click on. This makes new data immediately available.
The initial connection of Tubifex tubifex to the salmonid whirling disease parasite Myxobolus cerebralis was a shock to many. Tubifex tubifex is well known as the sewage sludge worm, and its widespread occurrence in western trout streams seemed doubtful. This led to 2 alternate hypotheses. The first alternate hypothesis is that there must be other worm hosts for this parasite. This could be true, but my field data give no reasons to believe so. I have now sampled 31 separate streams that are whirling disease positive and found Tubifex, or immature worms that are probably Tubifex, at all of them. Actually there is 1 negative site, but it has not yet been verified for location and there are many reasons to believe it is not correct. So what are the odds of finding Tubifex at 31 random trout streams in Montana? Bootstrapping the sites in my data base, which are definitely biased toward Tubifex positive sites should give a high estimate to this probability. That probability it turns out is too small to estimate accurately, but is somewhere around 1 in 5 million. We have far too many Tubifex-free streams for all whirling disease positive sites to have Tubifex, by chance alone. Still, this is circumstantial evidence.
I am also studying the whirling disease negative tributaries to whirling disease positive rivers and streams. Preliminary results, pending more fish sampling, seem to let most of our common worm species off the hook as candidate hosts. Only Ilyodrilus templetoni cannot be addressed this way as it always occurs with or downstream of Tubifex, or in warm springs that have no trout. This species is also the closest cousin to Tubifex in our trout streams, but it is limited to warmer streams.
The second alternate hypothesis is that Tubifex is not at all what we thought it was. That it is really a poorly known species, probably ubiquitous, maybe even invasive, but certainly not limited to polluted sites. My research and field data strongly suggest that all of these premises are wrong. Tubifex tubifex is very well known species with a large literature. That literature, my results and the views of leading worm experts are all in essential agreement. Tubifex tubifex is widespread, but not at all ubiquitous. We have many areas where it is not found. If Tubifex is, in fact, the only worm host, I can assure you that most of our pristine headwaters and their remnant cutthroat and bull trout will be quite safe from whirling disease. Tubifex is, in fact, almost entirely limited to polluted sites, and it is not invasive of unpolluted areas. It is the nature of the pollution that is frequently misunderstood.
It is most important to recognize Tubifex tubifex for what it is- a tramp! Tramps are nothing more than the animal equivalence of weeds, and as such they are characterized by 4 outstanding biological features. First is a tremendously wide environmental tolerance. You may think of T. tubifex as pollution tolerant, but it also tolerates extreme oligotrophic conditions. Second is an almost supernatural power of dispersal. With T. tubifex this is well documented, but the details are not at all well known. The young worms can encyst and the egg cocoons are quite tough. We need not worry about introducing Tubifex by itself- if conditions are right, it will be there on its own. If conditions are wrong, it will be quickly eliminated by predators and competitors. Third is rapid reproduction. Tubifex can mature quickly, breed anytime and all individuals deposit egg cocoons, which protect the young worms. So tramps and weeds are broadly tolerant, widely dispersing and great reproducers- why aren't they everywhere? The price they pay for all of the above is an almost pitiful ability to deal with the interactions, competition and predation, that occur in normal, diverse communities. So with a weed, if you clear away the native vegetation from a piece of ground- and it doesn't much matter what the native vegetation was or what the ground is like, the same damn weeds appear almost overnight, but they do not invade nearby undisturbed areas. Tubifex is the same- simplify the native benthic community and it will come. If the bacterial food source is rich they will be abundant and fast growing, and if the food source is poor they will be less abundant and more slow growing.
So the pollution Tubifex needs is anything that reduces the normal community diversity. In Montana this is usually livestock grazing or dams, but many other activities can contribute. Springs are about the only natural cause for Tubifex in Montana trout streams. Note the irony here- the water we normally think of as the most clean is naturally prone to Tubifex. Springs always have very low diversity compared to normal surface waters.
Tubifex is so broadly tolerant of the physical environment that there really is not any such thing as Tubifex physical habitat. Many see fine sediment as the key, but my observations strongly suggest that this is irrelevant to Tubifex, except for how it interacts with community diversity. When the community is really wiped out, Tubifex lives in or on all substrates including sand, gravel, cobble, boulders, bedrock, and concrete. Hatchery personnel need to known that concrete does not eliminate Tubifex, it just makes it easier to remove the worms by routine cleaning. The worms can be both large and abundant with only a couple millimeters of crud covering the surface.
Beyond the normal conditions required for most higher life, I have seen only 1 environmental limitation for Tubifex. It appears to be limited to cold or cool water, again contrary to the expectations of many. I hypothesize that recognizing Tubifex as a cool-water tramp will eventually explain much of the continent-wide variation in whirling disease severity. In our warmer trout streams and below, Tubifex takes on a long winter life cycle like many of our insects. The young worms appear in the fall, grow through the winter and mature and reproduce by the spring. The adults normally die after completing reproduction and they disappear with spring runoff. Cooler streams have no such pattern, even with large spring floods. This warm-water life cycle appears to be unfavorable to the parasite and may represent the downstream limit of the disease. This will vary from year to year. With the expected high water of this year, whirling disease may worsen in these areas.
It turns out that serious parasite outbreaks are often due to environmental change. Unnatural host populations and range shifts are usually to blame. With whirling disease we have unnatural fish communities created by introducing species from all over this continent and others, we have habitat degradation that allows the widespread expansion of Tubifex in western trout streams, and we have a parasite introduced from Europe. Just why is whirling disease so serious here? There should be no surprise and I am afraid it may just be the tip of the iceberg coming our way!
Whirling disease, treated as a fish health problem has no sure solutions in sight. Looking for resistant fish seems to be the best hope, but why a western North American species should be resistant to an western Eurasia parasite I do not known. It could happen, but still, the intentional further simplification of our once diverse western salmonids would not be my first choice for a solution.
Whirling disease, treated as an environmental problem has many obvious solutions, and we can be quite sure that they will work. Getting Tubifex out of hatcheries cures the disease in the hatcheries and getting the "pollution" out of streams gets rid of Tubifex in the streams. Both of these are already documented and the extension seems perfectly logical. So we already have a solution to whirling disease. We may lack the resolve, or the courage, or the clout, or the money, but we do have a solution. Moving forward with this totally in line with modern soil and water conservation practices that are already occurring in more developed areas. It will happen here eventually. With whirling disease, the economics of land and water abuse have changed and our land and water management practices need to be reevaluated.
06 FEB 1997 D.L. Gustafson
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