A comparison of reproduction, growth and acute toxicity in two populations of Tubifex tubifex (Müller,1774) from the North American Great Lakes and Northern Spain

Reproduction in Tubifex tubifex is being used as part of a suite of indicators of sediment toxicity in Canada and Spain, and reproduction of T. tubifex is being considered as a component of sediment objectives for environmental regulation and clean-up in the Canadian Great Lakes. The data being used to set these reproductive targets have been developed from a single culture of T. tubifex from Lake Erie. The plasticity of this particular species is well known and before it can be adopted widely as a test organism it is necessary to determine whether a single culture source should be used or if cultures derived from different populations respond similarly. A series of experiments with two cultures, one from Lake Erie the second from a small mountain stream in Northern Spain have shown that the Spanish worms appear to produce fewer cocoons per adult (mean 8.6 S.D. 1.0) than those from Lake Erie (mean 10.4 S.D. 0.3) at 22.5 °C, a standard test temperature. The number of young produced per adult by the Spanish culture is also lower (mean 19.0 S.D. 4.6) than the L. Erie population (mean 30.6 S.D. 2.3), however, the Spanish population has higher reproductions rates at a lower temperature. The Spanish worms also have lower and more variable growth rates than the Canadian population. There also appear to be slight differences in the sensitivities to toxicants, with the Canadian worms having higher LC50s for copper, chromium and cadmium. While there are differences in the responses in the two cultures these are not considered to be sufficient to invalidate the use of either population in a standard bioassay protocol as long as appropriate calibration and validation are undertaken.     

Countering morphological ambiguities: development of a PCR assay to assist the identification of <Emphasis Type="Italic">Tubifex tubifex</Emphasis> oligochaetes

The freshwater oligochaete, Tubifex tubifex, is a common resident of organic-rich sediments worldwide. Although it is a familiar species to fish enthusiasts, toxicologists and parasitologists, T. tubifex often confounds definitive identification due to the similarity that immature specimens bear to several other common oligochaetes, and given the degree of plasticity of key morphological characters due to environmental conditions and/or age of specimen. To solve this identity crisis, we used a polymerase chain reaction based molecular approach and developed a T. tubifex specific assay with primers that amplify a 192 bp fragment of the internal transcribed spacer region 1 ribosomal DNA. We tested these primers on four T. tubifex mitochondrial genotypes, and on other oligochaete species from nine genera. The primers amplified all specimens identified morphologically asT. tubifex. They did not amplify any other species, including morphologically similar worms possessing hair chaetae (Dero digitata, Ilyodrilus templetoni, Tubifex ignotus or Rhyacodrilus spp.) or other oligochaetes often found with T. tubifex (Lumbriculus variegates, Limnodrilus hoffmeisteri, Stylodrilus heringianus or Trichodrilus sp.). This technique should remove the uncertainties all too often associated with identification of T. tubifex.     

Ammonium excretion by some freshwater zoobenthos from a eutrophic lake

Relationships between the ammonium excretion rate of zoobenthos and temperature were examined for two chironomids, Chironomus, plumosus and Tokunagayusurika akamusi, one chaoborid, Chaoborus flavicans, and two tubificids, Limnodrilus spp. and Branchiura sowerbyi, which often dominate in eutrophic lakes. The representative Q₁₀ value and excretion rate at 15° C for each species were as follows: C. plumosus, 1.67, 1.40, (µg N mg dry w.^–1 d^–1 ); T. akamusi, 1.02 (< 15° C), 0.33; C. flavicans, 1.49, 2.87; Limnodrilus spp., 2.98, 0.59; and B. sowerbyi, 3.15, 0.79.     

Cyst formation of Tubifex tubifex (Müller) — an adaptation to survive food deficiency and drought

Adult individuals of Tubifex tubifex (Müller) (Oligochaeta, Tubificidae) could be induced to form cysts in the laboratory. Hiding in cysts, Tubifex tubifex survived a five-month drought period in the field. Encysted Tubifex tubifex had a lower super-cooling-point than mobile individuals. Food shortage is believed to be the main factor in cyst formation.     

Acute and chronic effects of an anionic surfactant on some freshwater tubificid species

We report the results of research on acute and chronic effects of linear alkylbenzensulfonate (LAS) on two tubificid species. 96 h LC₅₀ assay values were estimated at 10° for Limnodrilus hoffmeisteri and Branchiura sowerbyi exposed to different concentrations of LAS dissolved in water, both with and without sediment. The presence of sediments modified LAS toxicity and increased values: NOEC and LOEC resulted in values 2.5 times higher for Branchiura sowerbyi and 4–4.5 times for Limnodrilus hoffmeisteri, when the sediments were present. The chronic effects induced by a long exposure to LAS were evaluated for different stages of the biological cycle of Branchiura sowerbyi. Using concentrations between the NOEC and LOEC (0.5, 2.5, and 5 ppm), with control, we could observe that: 1) at 5 ppm the cocoons were laid precociously compared to controls, 2) in all treated series the number of cocoons was lower than in controls, 3) the mean number of oocytes per cocoon was lower for the worms submitted to LAS, compared to the control, 4) the period of embryonic development was similar for all used concentrations and for control, and 5) the number of degenerated cocoons was unchanged by the LAS treatment.     

Density-dependent processes in cohorts of Tubifex tubifex,with special emphasis on the control of fecundity

Laboratory cohort cultures of the tubificid Tubifex tubifex with different initial densities were carried out at 20° C with the condition of unlimited food. The main results were: 1) Intracocoon mortality was 37% of the laid eggs (observation of 689 eggs); 2) The principal bionomic parameters (generation time, r, R₀) appeared to be density dependent; 3) Recruitment was regulated through the percentage of worms that actually attained the ovigerous stage, specific fecundity, and the duration of the egg laying stage, which appeared to be inversely correlated with density.     

Population analysis in mass cultures of Tubifex tubifex

Mass cultures of Tubifex tubifex from Lake Orta were kept in the lab at 20 °C starting with different initial densities (10, 45, 86, 161 ind · jar^–1), with the aim of evaluating the effect of density on population numbers and on population parameters. The results show that density mainly controls fecundity, growth, maturation and ovigeration rates. Growth rates and mean number of eggs laid/ovigerous (R₀) are inversely related to density, but generation time appears to be directly related. Very low or very high initial densities display, at different times of the culture history, efficient density controls. Intermediate N₀ seem to bring about situations of bad control, easily leading to numerical overshoots. A possible implementation of a population dynamics model (Bonomi & Di Cola, 1980), originally used for laboratory observations on T. tubifex cohorts was considered, including some density control functions derived from our observations on cohort and mass cultures in some transfer rates and in fecundity rate.     

Aquatic oligochaete fauna (Annelida,Clitellata) in Lake Tonle Sap and adjacent waters in Cambodia

In surveys conducted during 2000–2005, 39 taxa of aquatic oligochaetes belonging to the families Enchytraeidae and Naididae were found in Lake Tonle Sap in the Mekong River Basin, Cambodia. Dominated by naidines and pristinines (29 taxa), they mainly comprised widely distributed species as well as South Asian and Southeast Asian species. Among the four areas studied, the littoral regions of the lake—where inundated forests and aquatic vegetation developed during the flooded seasons—presented the highest number of species. Submerged vegetation in the littoral Lake Tonle Sap harbored abundant epiphytic oligochaetes, especially Stylaria fossularis. In contrast to the rich abundance of naidine and pristinine fauna, tubificines and ryhacodrilines were scarce in and around the lake, irrespective of the vegetation in their habitats. Several Aulodrilus species and Branchiura sowerbyi were the main representatives of the benthic oligochaete assemblages throughout the offshore zone of the lake without vegetation. It is noteworthy that the widely distributed tubificines Tubifex tubifex and Limnodrilus hoffmeisteri were not found in any surveyed locality.     

Acute toxicity testing with the European estuarine amphipod <Emphasis Type="Italic">Corophium multisetosum</Emphasis>

This study reports on the use of the estuarine amphipod Corophium multisetosum in acute toxicity testing. The species was successfully acclimated to the laboratory and was used in a water-only whole effluent 96 h acute bioassay and in a 10 days whole estuarine sediment test. C. multisetosum response was compared to other species in 96 h bioassays, testing boiling cork effluent and iron filings lixiviates. The amphipod showed high sensitivity and the results were similar to those obtained with others species namely, the freshwater cladoceran Daphnia magna, the estuarine amphipod Gammarus chevreuxi and the seawater annelid Sabellaria alveolata. In a 10 days static exposure to natural impacted estuarine sediments, the response of the species was compared to a fertilization bioassay with the sea-urchin Paracentrotus lividus. Both species indicated the same sediment samples as the most potentially toxic. These samples were collected in sites where the resident macrofauna benthic community is also the most affected, with strong reduction of the species richness, abundance and biomass. The results revealed that C. multisetosum presents high potential to be used in routine acute toxicity testing in the estuarine environment.     

Production and population dynamics of Tubifex tubifex in the profundal zone of a freshwater reservoir in N. Italy

During a study of a pumped storage system from May 1979–June 1980 the profundal macrobenthos of the upper reservoir (Lago di S. Maria Valvestino) was sampled at a fixed station and the population of the tubificid Tubifex tubifex studied in detail. Eggs, embryos and the individuals living in an extra-cocoon stage were counted and individually weighed from monthly samples, according to the methods described in Bonomi & Di Cola (1980). Numerical recruitment during the study period was estimated as 257 000 ind m^–2 yr^–1; of which 110 000 died either as eggs or as embryos, i.e. inside the cocoons, and a further 128 000 died before they attained sexual maturation. The data seem to confirm the typical demographic strategy of T. tubifex i.e. high fecundity and high mortality in the early life stages. The total annual production of the species was estimated at 91.7 g (w.w.) m^–2. The low P/B ratio (2.0 yr^–1) is considered to be mainly due to high population densities.     

Observations on cohorts of Tubifex tubifex cultured at different food levels,using cellulose substrate

In order to clarify the relationship between food availability and population dynamics in aquatic oligochaetes, short term cultures and cohort cultures of Tubifex tubifex were reared using substrates with different food concentrations, obtained by mixing sand with different amounts of cellulose powder.In short term experiments, T. tubifex seemed capable of utilizing cellulose substrates for growth or egg production. Yet, in the cohort experiment, newly hatched worms could not grow on cellulose substrates. Survivorship, however, appears to be influenced by cellulose concentration giving an indication that this material, although inadequate, is somehow utilized.     

Tubifex tubifex as a link in food chain transfer of hexachlorobenzene from contaminated sediment to fish

Sediments contaminated with poorly water-soluble organic chemicals pose a risk to aquatic food chains. Sediment-associated chemicals can be accumulated by endobenthic, sediment-ingesting invertebrates. Some tubificid species – or other benthic annelids – serve as food for benthivorous fish, which thereby ingest the sediment-borne chemicals and may accumulate contaminant concentrations far higher than from water exposure only, and transfer them to organisms of higher trophic levels. For measurement of biomagnification, a sediment based food chain was developed and established in the laboratory. The two-step food chain included the sediment-dwelling freshwater oligochaete Tubifex tubifex (Müller) as a representative species of benthic infauna. The three-spined stickleback (Gasterosteus aculeatus, Linné), a small teleost fish which often feeds primarily on benthic invertebrates, served as a model predator. Spiked artificial sediment and reconstituted water as the overlying medium were used. Experiments were performed using ¹⁴C-labelled hexachlorobenzene, a hydrophobic pollutant as a model compound. To examine the influence of benthic prey on the bioaccumulation of the test substance in the predator, fish were exposed to spiked water, spiked sediment, pre-contaminated prey organisms, or combinations of these exposure routes. The results of these experiments indicate that for hexachlorobenzene, the presence of contaminated Tubifex tubifex as a food source in combined exposure leads to significantly higher accumulation in fish than exposure to single pathways.     

Expression pattern of annelid <Emphasis Type="Italic">Zic</Emphasis> in embryonic development of the oligochaete <Emphasis Type="Italic">Tubifex tubifex</Emphasis>

Embryonic expression of a Zic homologue (Ttu-Zic) was examined in the oligochaete annelid Tubifex tubifex. The body plan of T. tubifex is characterized by obvious segmentation in the ectoderm and mesoderm. Ttu-Zic expression is detected in the mesodermal germ band and a subset of micromere descendants. Ttu-Zic is transiently expressed in primary m-blast cells (i.e., founder cells of mesodermal segments) as early as the time of their birth from M teloblasts. During its development, each mesodermal segment experiences two additional phases of Ttu-Zic expression. Ttu-Zic expression in micromere descendants is seen on the anterior surfaces of embryos undergoing teloblastogenesis; subsequently, these cells proliferate to form bilateral clusters, which then become internalized. Finally, clusters of Ttu-Zic-expressing cells are found in the center of the prostomium, corresponding to the cerebral ganglion. The Ttu-Zic expression profile in the early embryogenesis of T. tubifex may be homologous to those of evolutionarily distant animals.     

Potential for aquatic oligochaetes as live food in commercial aquaculture

Aquatic oligochaetes may potentially become an important constituent in commercial aquaculture as a live food source. Tubifex tubifex, Limnodrilus species, Branchiura sowerbyi and the lumbriculid Lumbriculus variegatus have been economically mass cultured with production rates of 15 kg m^- and population doubling times of 11–42 days reported. Relatively high growth and survival rates of trout, salmon and sturgeon have been achieved in association with the use of this live food source. Benefits stem from advantages with increased appetites and palatability. As well, sanitation and heating requirements in fish hatchery situations may be reduced. Disease transmission must be prevented.     

Sediment toxicity in lakes along the river Kolbäcksån,central Sweden

The River Kolbäcksån system is located in a historical mining and steel works district of central Sweden. Ten years ago, intensive limnological studies indicated that the sediments in many of the lakes of this system were contaminated with metals and oil (grease). More recently a very high toxicity was found in the sediments from some of these lakes in tests with Daphnia magna and Tubifex tubifex. The objective of this study was to determine the toxicity to Daphnia magna of surficial sediments from representative locations (N = 39) within this system of lakes and to look for possible correlations with concentrations of metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) and oil (total) analysed in parallel samples. These results were also compared with spiked sediment toxicity data generated for these metals and with the bottom fauna at 8 of the 39 locations. Among the metals analyzed, only Cd, Pb and Zn were correlated with whole sediment toxicity. Only for Zn and Cr did the maximum concentrations approach those that were toxic in the spiked sediments. Correlations using single and combined metal contamination and toxicity (additive models) explained 16% of the sediment toxicity (r ² = 0.16; N = 39). Significant correlations with the bottom fauna in situ (gross abundance, biomass and species richness) were found for whole sediment toxicity, but not for metal contamination (N = 8). The use of the sediment quality triad approach for assessment of sediment quality is exemplified with a numerical normalization procedure for the latter 8 sites.     

Stromatinia cryptomeriae sp. nov., the teleomorph ofGloeosporidina cryptomeriae causing twig blight of Japanese cedar

A new species,Stromatinia cryptomeriae, is described based on a specimen collected in Iwate Prefecture, Japan. It was found on fallen dead branches and twigs of Japanese cedar,Cryptomeria japonica. The morphology of isolates on potato-dextrose agar (PDA), which were obtained from single ascospores ofS. cryptomeriae, was identical withGloeosporidina cryptomeriae, the causal fungus of Japanese cedar twig blight. In an inoculation test using single ascospore isolates, many minute black spots (sclerotioid bodies; sclerotules) and acervuli ofG. cryptomeriae were formed on the necrotic lesions, which developed into typical symptoms of Japanese cedar twig blight. These results show thatStromatinia cryptomeriae is the teleomorph ofG. cryptomeriae. On PDA, the fungus grew over a range of about 1 to 25°C, with the optimum growth at about 15–20°C.     

Preliminary investigations on the utilization of tubificid worms by postlarvae of Macrobrachium lanchesteri (de Man)

Postlarvae of Macrobrachium lanchesteri were stocked in confined waters. The larvae were fed on an ad libitum food of Tubifex tubifex worms for 30 days and their rearing has been established. 1 Kg of initially stocked postlarvae need 4.5 Kg of live T. tubifex to produce 0.537 Kg of new flesh. The worms were found to increase the crude protein content of larval flesh by 17% of the dry matter.     

Inorganic carbon fluxes at the water–sediment interface in five littoral systems in Spain (southern Europe)

The assemblage of littoral oligochaetes in six crater lakes in Central Mexico, was studied throughout a yearly cycle. To establish species composition, richness, density and biomass, 14 localities were sampled in the lakes. A total of eight species belonging to the families Naididae (five species), Tubificidae (two species), and Enchytraeidae (one species) were found. The dominant species, Limnodrilus hoffmeisteri, contributed with up to 99% in both abundance and biomass. Sediment organic matter is the most important environmental variable explaining the differences in density and biomass. Seasonal (dry and rainy seasons) changes were not significant for density and biomass. Higher density and lower biomass values characterized these lakes in contrast to other tropical and subtropical lakes worldwide. The small size of the dominant species L. hoffmeisteri was recorded in all lakes and explained the low biomass recorded in the area of study. The correlation between L. hoffmeisteri and four other species (Dero (Dero) nivea, D. (D.) digitata, Nais variabilis and Tubifex tubifex) was negative. The naidid species were positively correlated (>0.5) to each other.     

Long-term experiment on Branchiura sowerbyi Beddard (Oligochaeta,Tubificidae) using sediment treated with LAS (Linear Alkylbenzene Sulphonate)

A long-term experiment was performed with Branchiura sowerbyi in order to assess possible effects of LAS sorbed to sediment on its reproductive cycle, using concentrations in sediment 2–5 times higher than those calculated for the LC50 values of LAS dissolved in water. No significant effects were observed during the whole experiment, so that we can confirm that LAS adsorbed on sediment has a much lower influence on the examined animals than LAS dissolved in water.     

Community metabolism on rocky-shore assemblages in a mesocosm: A. Fluctuations in production,respiration, chlorophyll a content and C:N ratios of grazed and non-grazed assemblages

Studies were undertaken with the aim of developing a standardized method for assessing environmental pollution in sediments by utilization of life-history data of freshwater tubificids. Similar bioassay methods have long been used for Daphnia magna, species of Ceriodaphnia and Nitocra, etc. in accordance with guidelines from the International Organization for Standardization (ISO). Tubifex tubifex was found to be the most likely candidate for such bioassays, since the species is readily kept in culture and reproduces more or less consistantly.The culturing method is slightly modified from Kosiorek (1974). This paper provides an example of the particular sensitivity of this kind of bioassay method in the detection of heavy metal contamination of lake sediments. Sediments from the oligotrophic Lake Runn were considered suitable for the purpose, since the lake receives waste water from a major mining industry in Sweden. Metal analyses of the sediments had revealed the agents likely to be causing the decreased biological activity measured in the lake; rough amplitudes for mercury: 800–3600 ng · g^-1 dw, copper: 800–1800 g · g^-1 dw, zinc: 3.3 – 8.1 mg · g g^-1 dw have been estimated for surficial sediments.Young tubificids exposed to Lake Runn sediments did not grow much and died off within a short period of time. No reproduction occurred. Sediments from Lake Runn, when mixed with sediments from the eutrophic Lake Hjälmaren, made reproduction of T. tubifex occur only in mixtures containing less than 50% L. Runn sediments. The growth rate, reproductive success and the very timing of consecutive reproductive events of cohort individuals were found to be highly indicative of toxic effects. When additional food sources were available, however, these effects were largely masked. Therefore, extra food rations were excluded from the original method.