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The freshwater euryhaline oligochaete Limnodrilus hoffmeisteri was selected for use in bioassays with polluted sediment from Santander Bay. It is easy to culture; is tolerant of low to moderate, up to 15‰, salinity; and is common in oligohaline conditions in European and North American estuaries. Worms were collected from an estuarine population and kept in unpolluted sediment for between 2 and 4 weeks, under laboratory conditions, at 7–8.5‰ salinity and 22.5 °C. Sediment from different sites in Santander Bay were sieved through 250 μm mesh and adjusted to a salinity of approx. 7‰ prior to the bioassays, either by adding sea water or dechlorinated tap water to the overlying water. High levels of ammonia in some sediment, which may confound results in ecotoxicity bioassays, were reduced by oxidation of the sediments in shallow trays. Sediment bioassays were performed with sexually mature Limnodrilus hoffmeisteri worms in 250-ml beakers, with a 1:3 ratio of sediment:water and 4 worms per baker. Endpoints in the 14-day bioassay were % mortality, adult final biomass, % adults that have shown resorption of the clitellum, number of cocoons, and burrowing behaviour. It was possible to rank the sites according to their toxicity using both mortality rates and sublethal effects. The control site had the following values for the endpoints: 5% mortality, ( $$\overline{x}\pm {\rm sd}$$ ) 2.40 ± 1.52 cocoons per beaker and 1.271 ± 0.470 mg dw adult final biomass. The most toxic sediment resulted in 65% mortality, resorption of the clitellum in 67% of the adults, no production of cocoons and a low final biomass ( $$\overline{x}\pm {\rm sd}$$ =0.681 ± 0.489 mg dw per adult). A second site had high mortality (60%) and no reproduction, although resorption of the clitellum did not occur in surviving animals. The remaining sites showed similar mortality (35–42%), and at only one of them was low reproduction observed (0.8 ± 0.447 cocoons per beaker). Behavioural effects, measured as length of galleries in a fixed area of the test-vessel at the end of the bioassay, were significant compared with control at only one site. Multivariate analysis showed the mortality gradient to be the strongest, with a second unassociated gradient representing clitellum resorption. The mortality gradient was associated with Cu and Zn concentration, and PAH and Pb possibly with resorption. [ABSTRACT FROM AUTHOR]

The behaviour of Polycelis nigra (Müller). P. tenuis (Iiima), Dugesia polychroa (Schmidt) and Dendrocoelum lacteum (Müller) in terms of their competition for food was studied in the laboratory. Activity of each species in the absence of food was minimal with P. tenuis showing the most. Speed of arousal by prey fluids was timed and it varied with the prey. Preference for any of these prey fluids was tested using a Y-maze. Chemosensory discrimination between three prey fluids offered in pairs did occur and some preferences were shown. Using a scentless nylon bristle it was demonstrated that each species turned towards a gentle contact stimulus and this was taken to be appetitive behaviour. The responses shown are considered to be integral to the competition for food amongst these four species. [ABSTRACT FROM AUTHOR]

The article presents evidence for intra-specific competition in field populations of triclads. It stresses thet sessile habit of these plants explains the more satisfactory demonstrations of competition by botanists. The article also notes that the species is widespread in Britain and lives under variable biological conditions. Breeding occurs over most of the year but there are two peaks, a larger one in early spring and another in later summer. It explains that triclad populations in this account illustrate intra-specific competition well through determining the special characteristics of animals and special conditions.

The population dynamics of Polycelis nigra, F. tenuis and Dugesia polychroa were studied in laboratory ecosystems provided with a constant supply of natural food and maintained under a temperature regime which followed that of an outdoor pond. The same phenomena, related to breeding, such as shrink-age of adults, mortality of small individuals and curtailment of egg production occurred in these populations as was observed earlier in field populations. Analysis of size-structure, population numbers and biomass suggested that the major changes were the result of intraspecific competition for food. Experiments to study the effect of varying the population density of triclads upon food up- take, under conditions of a constant food supply, showed that competition may occur although all the food is not utilised. This was attributed to the aggregation of triclads on individual prey. Certain anomalies in the performance of some of the populations were considered to be partly due to chance events in this feeding behaviour of triclads. It was shown that while exocrene substances influenced the fecundity of triclad populations this was a minor factor compared with intraspecific competition for food. [ABSTRACT FROM AUTHOR]

1) The life-cycle and population biology of Dendrocoelum lacteum living in a small pond is described. 2) Data of numbers, size and breeding activity were obtained by taking quad rat samples and from the examination of refuges placed in the habitat. Sampling took place once a fortnight by using the methods alternately, over two years. 3) There was an annual cycle in the number of adults, in the incidence and intensity of breeding and recruitment of young. These were indicated in the size-structure of the population and total numbers, 4) Approximate estimates of fecundity suggested a minimal value of 4.9 and a maximal value of 6.9 young per adult. 5) Changes in the numbers of prey organisms were recorded and their bearing on the population of D. lacteum discussed. 6) Breeding occurred from December to August with a peak around May. Recruitment of young started in April, reached a peak in June and ceased by September/October. Adults declined in numbers throughout the breeding season, initially due to mortality, later due to shrinkage. Total numbers reached a peak in July toward the end of breeding and thereafter declined to an approximately stable pre-breeding number. 7) This annual cycle stems from breeding which ultimately causes intra-specific competition for food. This is relieved by mortality. The main prey organism involved is Asellus meridian us and its annual cycle of numbers fits the hypothesis. 8) The population dynamics of Dendrocoelum lacteum and the three planariid species, Polycelis nigra (Müll), P. tenuis (Ijima) and Dugesia lugubris (O. Schmidt) are compared briefly. [ABSTRACT FROM AUTHOR]

1. The taxonomy of the Dugesia lugubris-polychroa species complex is briefly discussed. 2. The breeding biology of Dugesia lugubris (O. Schmidt) living in a small, eutrophic pond is described and supplemented by laboratory observations. 3. Changes in the size-structure and proportions of adult and young were observed at monthly intervals and showed an annual cycle of events. Adults reached a peak in early summer (June) just after breeding commenced and relative numbers declined markedly to a minimum in Sept. Recovery commenced in Oct. 4. These changes can be related to the appearance of young in the summer which seemed to produce an acute food shortage. Comparison of fecundity in the field and laboratory supported this explanation. It was confirmed by a field experiment in which the addition of food prevented the summer decline of adults and increased fecundity almost four-fold. 5. The condition of the reproductive organs of large-sized individuals was examined by sections and discussed in relation to population events. [ABSTRACT FROM AUTHOR]

1. The breeding biology of a population of Polycelis temuis Ijima living in a small, eutrophic pond is described and supplemented by laboratory observations. 2. Changes in the size structure of this population observed at monthly intervals showed an annual cycle of events. Adult numbers reached a peak in early spring just prior to breeding, declined markedly during breeding and then began to recover in the autumn after the cessation of breeding. 3. These events can be geared to the appearance of young in the spring which ultimately seemed to produce a crisis in availability of food to the entire population. 4. Comparison of fecundity in the laboratory and the field confirmed the periodic existence of food shortage and consequent low fecundity in nature. 5. The condition of the reproductive organs of large-sized individuals from natural populations fitted the interpretation placed on field events. [ABSTRACT FROM AUTHOR]

1. The current taxonomy of the 12 or 13 British species of freshwater triclads is discussed and drawings for identification provided. 2. Ninety lakes, tarns and ponds from 6 areas in northern Britain have been sampled during the summer period for triclads and certain of the chemical properties of the water measured. Lakes etc. selected for study were restricted to those with an area of less than 1 sq. mile and collections confined to gently shelving, non-exposed, stony shores. 3. A quantitative sampling method was used for triclads which is shown to provide valid data for determining population trends. 4. Some general features of these lakes are described. By selecting a wide range of soil type and utilisation of the drainage area, a corresponding range in lake productivity, as indicated by the chemical features of the water, was provided. 5. As lakes become more productive the number of triclad species which they contain increases from 0 to 5. Polycelis nigra is most tolerant of conditions followed by P. tenuis and P. hepta, while Dugesia lugubris and Dendrocoelum lacteum are confined to more productive lakes. Phagocata vitta inhabits only the more unproductive takes above 500 ft. Polycelis felina is an important lake-dwelling species numerically in Scotland. 6. The triclad faunas of the western islands, Anglesey, Islay and the Isle of Man are less varied than those of the mainland. 7. It is shown that a highly significant, positive relationship exists between the total triclad populations and the calcium and dissolved matter contents of lake waters, particularly the latter. This relationship is modified by such factors as lake altitude, the amount of pollution a lake receives, exposure of the shore to wave action, dystrophy etc. It probably depends on a greater avail- ability of food as lake productivity increases. 8. Analysis of comparable lakes in the various regions shows that there is a broad agreement between climate as evidenced by air temperature, and triclad abundance; higher temperatures being more favourable. The N. Ireland lakes support the highest populations and this is very tentatively attributed to greater pollution. 9. A comparison of the trends of mono-specific populations shows that P. nigra is adversely influenced by the presence of other species in the genus. The cause of this is unknown but circumstantial evidence suggests competition for food as a likely factor. There is only slight evidence for inter-generic effects between Polycelis and Dugesia plus Dendrocoelurn but the data are few. 10. A basis for using triclads to assess lake productivity or type, is suggested. [ABSTRACT FROM AUTHOR]

Two sediment bioassay methods using Tubifex tubifex (Muller, 1774) as the test species were compared. The first was an adult reproductiontest, the second an early-life-stage survival test. The duration of both bioassays is 28 d and the amount of work required was similar; they may be useful alternatives to each other in different circumstances (e.g., the early life stage bioassay could be carried out with smaller volumes of sediment). The two bioassays were performed simultaneously on copper-spiked sediments. Sediments from two freshwater and two terrestrial sites were used; five separate, non-simultaneous experiments were performed, one for each sediment or soil and a further experiment with soil with a food supplement. In the adult bioassay, there were large differences in the production of cocoons, eggs, and young among the control treatments of the five experiments. There were also major differences in the NOEC (no-observed-effect concentration) and LOEC (lowest-observed-effect concentration) for copper between the tested substrates. The early life stage bioassay appears to be lesssensitive to copper toxicity than the adult reproductive bioassay since NOECs and LOECs are higher for early survival than for the most sensitive endpoints of the adult bioassay in three experiments out of five. [ABSTRACT FROM AUTHOR]