Disclaimer & Copyright Notices; Optimized for the MS Internet Explorer
Soil & Water Conservation Society of Metro Halifax (SWCSMH)
Updated: October 09, 2013
Oligochaetes are common in most freshwater
habitats, but they are often ignored by freshwater biologists because
they are thought to be extraordinarily difficult to identify. The
extensive taxonomic work done since 1960 by Brinkhurst and others,
however, has enabled routine identification of most of our freshwater
oligochaetes from simple whole mounts. Some aquatic worms closely
resemble terrestrial earthworms while others can be much narrower or
thread-like. Many aquatic worms can tolerate low dissolved oxygen and
may be found in large numbers in organically polluted habitats.
Aquatic worms can be distinguished by:
- Body colour may be red, tan, brown or black.
- Cylindrical, thin (some are very thin), segmented body may be upto 5 inches.
- May have short bristles or hairs (setae) that help with movement (usually not visible).
- Moves by stretching and pulling its body along in a worm-like fashion.
Four families in the orders Tubificida
and Lumbriculida are common in freshwater in northeastern North
America: the Tubificidae, Naididae, Lumbriculidae, and Enchytraeidae.
In addition, freshwater biologists sometimes encounter lumbricine
oligochaetes (order Lumbricina; the familiar earthworms), haplotaxid
oligochaetes (order Haplotaxida; rare inhabitants of groundwater), Aeolosoma (class Aphanoneura; small worms once classified with the oligochaetes), and Manayunkia speciosa (class Polychaeta) in waters of northeastern North America.
- The tubificids probably are the best
known of the freshwater oligochaetes. They are most commonly found in
soft sediments rich in organic matter, and several species
characteristically live in sites that receive organic pollution. Like
all aquatic oligochaetes, tubificids respire cutaneously, but a unique
feature of this family is that some species can tolerate anoxic
conditions. Most tubificids are deposit feeders, subsisting on organic
detritus and its associated microflora. A few of the tubificids of
northeastern North America reproduce predominantly by fragmentation
(e.g., Aulodrilus spp. and Tasserkidrilus harmani), but most are sexually reproducing hermaphrodites.
- The Naididae is an
ecologically diverse family of worms common in both running and
standing waters. Many naidids are sediment dwellers, like the
tubificids, but other species are characteristically found among
aquatic plants. The family Naididae includes detritivores (e.g., Specaria josinae), algivores (e.g., Amphichaeta americana), carnivores (e.g., Chaetogaster diaphanus), and even a parasite of snails (Chaetogaster limnaei). Sexual reproduction is rare in most species. Reproduction occurs predominantly by paratomy.
- Only three species in the family Lumbriculidae occur in northeastern North America, and only two of them (Stylodrilus heringianus and Lumbriculus variegatus)
are common and widespread. These large worms are found in standing and
running waters, and are ecologically somewhat similar to tubificids.
- Enchytraeids are common in
marginal aquatic habitats-- marshes, small streams, springs, and
interstitial waters along the margins of streams-- and they are found
occasionally in the sediments of lakes and rivers as well. Because of
taxonomic difficulties, very little work has been done on the ecology
of freshwater enchytraeids in North America.
Of the freshwater annelids, the oligochaetes
display the greatest diversity and have the greatest indicator value.
The two families, Naididae and Tubificidae form 80 to 100% of the
annelid communities in the benthos of most streams and lakes at all
trophic levels (Mackie, 2001).
Oligochaetes are common in most
freshwater habitats, but they are often ignored by freshwater
biologists because they are thought to be extraordinarily difficult to
identify. The extensive taxonomic work done since 1960 by Brinkhurst
and others, however, has enabled routine identification of most of our
freshwater oligochaetes from simple whole mounts. Some aquatic worms
closely resemble terrestrial earthworms while others can be much
narrower or thread-like (Peckarsky et al, 1990).
- Oligochaete worms are diverse, and occur
in a spectrum of fresh waters, from unproductive to extremely eutrophic
lakes and rivers.
- As lakes become organically polluted and dissolved
oxygen concentrations become reduced or are eliminated, an abundance of
tubificid oligochaetes is commonly found concomitant with a precipitous
reduction and exclusion of most other benthic animals. As long as some
oxygen is periodically available, and toxic products of anaerobic
sedimentary metabolism do not accumulate, the rich food supply and
freedom from competing benthic animals and predators permit rapid
- Oligochaete densities can be very large (many
thousands per sq.m.). Productivity can vary greatly from year to year
because of changes in mortality associated with population dynamics of
major long-lived predators (e.g. chironomid midge larvae).
The tubificids are gatherers, feeding on
detritus in the sediments. They are the only worms present in the
deepest regions of lakes and are represented by several indicator
species. (Mackie, G.L. 1998. Applied Aquatic Ecosystem Concepts.
University of Guelph Custom Coursepack. 12 chapters.).
- The classical "pollution indicators" are Tubifex tubifex and Limnodrilus hoffmeisteri.
Both species are able to survive periods of anoxia, such as occurs in
the hypolimnia of eutrophic lakes during the summer and winter months.
Most tubificids have erythrocruorin, a red blood pigment, that
effectively extracts oxygen dissolved in the water. The densities of T. tubifex and L. hoffmeisteri in sewage lagoons may be so high that the bottom appears pink.
- Though, not all tubificids are pollution indicators. Some species, such as Tubifex kessleri and Peloscolex variegatum, require well oxygenated waters and reach their greatest densities in oligotrophic lakes.
References and web URLs:
- Kellogg, L.L.
1994. Save Our Streams. Monitor's Guide to Aquatic Macroinvertebrates.
Second Ed. Izaak Walton League of America. 60p.
- Mackie, G.L. 2001. Applied Aquatic Ecosystem Concepts. Kendall/Hunt Publishing Company. xxv, 744 pp. ISBN 0-7872-7490-9
- Pennak, Robert W. 1978. Fresh-Water
Invertebrates of the United States. Second Edition. John Wiley &
Sons. ISBN: 0-471-04249-8. xviii, 803p.
- Peckarsky, B.L., P.R. Fraissinet, M.A.
Penton, and D.J. Conklin, Jr. 1990. Freshwater Macroinvertebrates of
Northeastern North America. Cornell Univ. Press. xii, 442pp.
We salute the Chebucto Community Net (CCN) of Halifax, Nova Scotia, Canada for hosting our web site, and we applaud its volunteers for their devotion in making `CCN' the best community net in the world