Crustacean assemblage and environmental characteristics of a man-made solar saltwork in southern France,with emphasis on anostracan (Branchiopoda) population dynamics

Physical and chemical variables, anostracan populations (Artemia parthenogenetica and Branchinella spinosa) and other biota were studied during 1996–1997 in a Camargue saltern (max. depth 1 m). The taxonomic composition and density of macroinvertebrates were investigated twice monthly, based on benthic substrate and water column samples. Fauna was composed of three groups in terms of numerical importance. The benthic macroinvertebrates were represented only by nematodes (< 50 ind. m^–2 to > 500 ind. m^–2 in November–December and May respectively). The zooplankton was dominated by crustaceans, one cladoceran, Moina salina (ranging from 670 to 2350 ind. m^–2 in spring), two anostracans, Artemia parthenogenetica (< 50 ind. m^–2 in autumn), and Branchinella spinosa (max. 190 ind. m^–2 in December to absent in April), and two copepods, Cletocamptus retrogressus (max. density 2000 ind. m^–2 in November), and Eurytemora velox (max. density 650 ind. m^–2 in February–March). Insects (Chironomidae, Culicidae) were rare, with mean densities < 1 ind. m^–2. The phenology of each crustacean population is discussed in relation to physical and chemical water variables. Salinity appeared to be of greatest importance regulating the population abundance.     

The response of rice to the growth and nitrogen fixation inAzolla caroliniana andAzolla pinnata at varying rates of phosphate fertilization

The response of rice toAzolla caroliniana, newly introduced in India, was compared with the reponse to the local isolate ofAzolla pinnata at varying rates of phosphate fertilizer (4.4–8.8 kg P ha^–1) during a wet and a dry season.Fresh weight, dry weight and fixed N were more for both species 21 DAI (days after inoculation) than 14 DAI, but acetylene reduction activity (ARA) was higher 14 DAI than 21 DAI. Dry weight of Azolla and fixed N were less 14 DAI forA. caroliniana than forA. pinnata during the wet season. Twenty-one DAI, fresh weight ofA. caroliniana was 62.1 and 27.6% higher than that ofA. pinnata during the wet and dry season, respectively. However, dry weight and fixed N were more 21 DAI inA. caroliniana than inA. pinnata during only the wet season. The ARA was higher inA. caroliniana both 14 and 21 DAI, irrespective of season. The presence of either species in the rice field increased grain yield, straw yield, number of panicles m^–2, number of grains per panicle and reduced percentage sterility during both the wet and the dry season. Phosphate application significantly increased fresh weight, dry weight, ARA and fixed N for both species as well as grain and straw yields of rice. The responses to phosphate fertilizer were similar for both Azolla species and for rice grown with either one of the Azolla species.     

Stomatal conductance in a tropical xerophilous shrubland at a lava substratum

Diurnal variation in leaf stomatal conductance (g _s) of three xerophilous species (Buddleia cordata, Senecio praecox and Dodonaea viscosa) was measured over a 10-month period during the dry and wet seasons in a shrubland that is developing in a lava substratum in Mexico. Averaged stomatal conductances were 147 and 60.2 (B. cordata), 145 and 24.8 (D. viscosa) and 142.8 and 14.1 mmol m^–2 s^–1 (S. praecox) during the wet and dry season respectively. Leaf water potential () varied in a range of –0.6 to –1.2 (S. praecox), –0.6 to –1.8 (B. cordata) and –0.9 to –3.4 MPa (D. viscosa) during the same measurement periods. Stomata were more sensitive to changes in irradiance, air temperature and leaf–air vapour pressure difference in the rainy season than the dry season. Although stomatal responses to were difficult to distinguish in any season (dry or rainy), data for the entire period of measurement showed a positive correlation, stomata tending to open as increased, but there is strong evidence of isohydric behaviour in S. praecox and B. cordata. A multiplicative model relating g _s to environmental variables and to accounted for 79%–83% of the variation of g _s in three sites (pooled data); however, the performance of the model was poorer (60%–76%) for individual species from other sites not included in the pooled data.     

Winter Host Plant Specialization in a Host-Alternating Aphid

The host alternating aphid, Rhopalosiphum padi (L.), feeds in summer on several different species of grasses but is monophagous on its winter host, Prunus padus L. The monophagy on P. padus could be a result of the restricted host range of the several different generations colonizing, or feeding, on this host during autumn–winter–spring. This study shows that the winter host plant specificity of R. padi is controlled mainly by the preference of the females remigrating (gynoparae) to the winter host, P. padus, in autumn. The other generations living on the winter host, i.e., sexual females, males, and spring generations, all accept a broader range of winter hosts. One alternative host plant, Prunus spinosa L., could be utilized by all generations associated with the winter host, except for the females remigrating at autumn.     

Abundance of two threatened woodpecker species in relation to the proportion of spruce plantations in native pine forests of western Norway

In a comparative study we investigated woodpecker abundance in forest landscapes with different proportion of native pine forest and spruce plantations in western Norway. In 100 circular study plots of 100ha each we recorded 38 white-backed –Dendrocopos leucotos, 22 grey-headed –Picus canus, 13 great spotted –Dendrocopos major, 6 green –Picus viridis, and 2 lesser spotted –Dendrocopos minor woodpeckers in the breeding season. The mean number of recorded woodpecker species peaked at 20–40% spruce plantations. The two most common species in the study, the white-backed and the grey-headed woodpeckers are both Red-listed species in Norway and among the rarest woodpeckers in Europe. The white-backed woodpecker preferred plots with higher than average proportions of standing dead trees and deciduous trees, and low proportions of spruce plantations in the plots. The grey-headed woodpecker preferred plots in the western (coastal) parts of the study area with presence of large aspen Populus tremula trees. Logistic regression models did not reveal any clear threshold values with respect to proportion of spruce plantations in plots, although both woodpecker species were extremely rare in plots with >60% spruce plantations. We recommend spruce plantations to be kept at moderate levels to ensure viable populations of woodpeckers in western Norway.     

Distribution of sawfishes (Pristidae) in the Queensland Gulf of Carpentaria,Australia, with notes on sawfish ecology

Synopsis Pristis microdon, P. zijsron, P. clavata and Anoxypristis cuspidata are distributed throughout the Queensland section of the Gulf of Carpentaria, Australia. In a survey of the four species, Anoxypristis cuspidata was the most abundant and was recorded in both the inshore and offshore set net fisheries. The size distribution and catch locations of A. cuspidata suggest that the inshore area to a depth of 10 m may be the preferred habitat for juveniles of this species, while adults primarily occur offshore. Pristis microdon, P. zijsron and P. clavata were recorded only in the inshore fishery with catches dominated by immature animals. Pristis microdon was caught in the inshore fishery late in the monsoonal wet season (February to April) and inhabited both freshwater and estuarine environments. Pristis zijsron occurred only on the sand and mud flats outside river mouths whilst P. clavata inhabited both the sand and mud flats and upstream estuarine habitats. Observations on reproductive staging and the capture of neonate specimens suggest that in all four pristids, pupping occurred through the wet season until the beginning of the dry season in May. A seasonal set net closure for the barramundi, Lates calcarifer and shark fisheries, which has been in place since 1980 in Queensland Gulf waters, therefore offers a measure of protection to breeding female sawfish and their offspring.     

Effect of salinity on competition between the rotifers Brachionus rotundiformis Tschugunoff and Hexarthra jenkinae (De Beauchamp) (Rotifera)

We studied the effect of different concentrations (0, 3, 6, 9 and 12 g l^–1) of sodium chloride at one food level of Chlorella (1×10⁶ cells ml^–1) on competition between the rotifers B. rotundiformis and H. jenkinae, both of which were isolated from a saline lake. The population growth experiments were conducted for 3 weeks. Both the rotifer species did not survive beyond one week at a salinity of 0 g l^–1. Regardless of salt concentration and the presence of a competitor, H. jenkinae reached higher densities than B. rotundiformis. When grown alone, both B. rotundiformis and H. jenkinae showed optimal peak population densities at the salinity of 6 and 9 g l^–1. Since biomass wise, B. rotundiformis was larger than H. jenkinae, it showed a lower numerical abundance. Thus, the maximum peak population densities of B. rotundiformis and H. jenkinae recorded in this study were 107±3 and 203±28 ind. ml^–1. The maximal rates of population increase for B. rotundiformis and H, jenkinae when grown alone were 0.264±0.003 and 0.274±0.004, respectively. Our results also indicated that B. rotundiformis and H. jenkinae coexisted better at a salinity of 6 and 9 g l^–1 of sodium chloride while a salinity of 3 g l^–1 favoured Hexarthra over B. rotundiformis. At 12 g l^–1, both the rotifer species grown alone or together showed lower growth rates compared to those at lower salinity levels. Except 0 g l^–1, in all other salinity treatments, H. jenkinae was a superior competitor to B. rotundiformis.     

Growth of dominant zooplankton species feeding on plankton microflora in Lake Shira

Batch cultures and continuous flow cultures were used to study the growth rates of zooplankton species from Shira lake, the rotifer Brachionus plicatilis Muller and calanoid copepod Arctodiaptomus salinus Daday, which were fed on phytoplankton and bacterioplankton from the lake. Analyses of the birth and survival rates were used to demonstrate that the lake phytoplankton, consisting mostly of cyanobacteria and diatomaceous algae, is inadequotes for optimal realisation of the reproductive potential of B. plicatilis when compared with the bacterial diet. The study revealed that the kinetic growth characteristics of the two zooplankters were similar: B. plicatilis r _max, 0.120 d^–1; S ₀, 0.253; and K _s, 0.114 mg dry mass l^–1; and for A. salinus r _max, 0.129 d^–1; S ₀, 0.240; and K _s, 0.171 mg dry mass l^–1. Fluctuations in natural food concentration reduced the growth rate of both species. Even though the threshold concentration of food for B. plicatilis and A. salinus were quite similar, the copepods were less sensitive to food limitation.     

Activity of pupal parasitoids of the stable fly Stomoxys calcitrans and prevalence of entomopathogenic fungi in the stable fly and the house fly Musca domestica in Denmark

A survey was conducted on confined dairy cattle farms and a pig farm from May–October in 1999 to determine the activity and relative abundance of pupal parasitoids and the prevalence of entomopathogenic fungi in populations of the haematophagous stable fly, Stomoxys calcitrans (Diptera: Muscidae), in Denmark. Four species of pteromalids were found with Spalangia cameroni as the predominant. The other parasitoids were S. nigripes, S. nigra and Phygadeuon fumator (Ichneumonidae). Peak activity of the parasitoids was observed to be late in the summer and the beginning of autumn (August–September) when approximately 10% of the collected stable fly pupae were parasitised. Adult stable flies were infected with four species of entomopathogenic fungi: Entomophthora muscae, E. schizophorae, Beauveria bassiana and Verticillium lecanii. All fungi occurred in low percentages (max. 4%) and remained at this level throughout the sampling period. Likewise, adult house flies were infected with B. bassiana and V. lecanii,but Metarhizium anisopliae, Paecilomyces fumosoroseus and V. fusisporum were also recorded. The overall hyphomycete prevalence in house flies was 0.3%, and single species rarely exceeded 0.1%. The prevalence remained low in spite of increasing house fly numbers in August–September.     

Dormant egg bank characteristics and hatching pattern of the Phallocryptus spinosa (Anostraca) population in the Makgadikgadi Pans (Botswana)

The anostracan Phallocryptus spinosa has an almost exclusively palearctic distribution. The Makgadikgadi Pans area in Botswana represents the only distribution record south of the Sahara. In this ephemeral wetland, it is an important food item in the diet of migrating birds. By studying egg bank characteristics (such as depth and density) and hatching requirements, we investigated the persistence of this sub-Saharan population. At localities in the middle and north basin of Sua Pan, sediment cores were taken along a transect, and dormant eggs were isolated. Densities of the active dormant egg bank ranged from 833 to 31449 dormant eggs m⁻², indicating that this species is well established. Most of the dormant eggs were found in the top 4 cm of the sediments, and densities decreased to zero at a depth of 13 cm. Considering the expected low sedimentation rate, the presence of dormant eggs down to 13 cm indicates long-time occurrence of P. spinosa in the Makgadikgadi Pans area. We observed high hatching fractions (up to 85%) at a temperature of 22 °C and a salinity of 5 ppt. A second anostracan species, Branchinella ornata, co-occurred with P. spinosa in our study site. This population also had a large active dormant egg bank (ranging from 6634 to 50557 dormant eggs m⁻²) with dormant eggs present until a depth of about 11 cm. This pattern indicates a long-time co-occurrence of P. spinosa and B. ornata.     

The assessing of Pacific oyster (Crassostrea gigas) rearing performances by the IFREMER/REMORA network: method and first results (1993–98) in Brittany (France)

Parasitological monitoring was carried out from 1997 to 1999 in a highly saline (41–45 g/l) lake in southeastern California, Salton Sea. A total of 1473 fishes were examined. Young tilapia, Oreochromis mossambicus, croaker, Bairdiella icistia, and mudsucker, Gillichthys mirabilis, were found infected by ectoparasites. Some persistent foci of fish infestations were found around the perimeter of the lake. The diversity of parasites was limited to three protozoan species, Amyloodinium ocellatum (Dinoflagellida), Ambiphrya ameiuri (Peritricha), Cryptobia branchialis (Bodonida: Kinetoplastida), and two metazoans, the monogeneans Gyrodactylus olsoni and G. imperialis. Both A. ocellatum and A. ameiuri infested fish from spring through fall. The greatest infestations occurred in summer (29–40°C) in the case of A. ocellatum and in spring and autumn (22–27°C) in the case of A. ameiuri. High parasite loads caused severe damage to such respiratory organs as gills and skin. They may depress respiration and osmoregulation and, in combination with other environmental factors, cause fish suffocation and death. These parasites may play a major role in juvenile fish mortality.     

The effect of rainfall on tick challenge at Kyle Recreational Park,Zimbabwe

The effect of rainfall pattern on tick challenge was investigated at Kyle Recreational Park, Zimbabwe, from 1991 to 1992 using drag and removal plot methods to sample environmental tick density. The abundance of adults and nymphs of the brown ear-tick Rhipicephalus appendiculatus and larvae of the bont tick Amblyomma hebraeum was positively correlated with monthly rainfall, whereas no relationship with rainfall was revealed for larval R. appendiculatus, adults of the red-legged tick R. evertsi, or larvae of the blue tick Boophilus decoloratus. A comparison between 1991 (490 mm rainfall) and the drought year of 1992 (161 mm) revealed significant differences in the abundance of R. appendiculatus, A. hebraeum, and B. decoloratus. During the wet season, R. appendiculatus adults were 2–3 time more numerous in the environment during the higher rainfall year of 1991. A. hebraeum larval abundance exhibited a similar pattern to that of R. appendiculatus adults, but B. decoloratus larvae were more abundant in the drought year of 1992 during both the wet and dry seasons. Comparable tick abundance data collected at Kyle during the above-average rainfall years of 1975–1977 (mean = 1029 mm) were compared with tick challenge during the below-average rainfall years of 1991–1992 (mean = 326 mm). In grassland sand habitat and all habitats combined R. appendiculatus adults, nymphs, and larvae were much more abundant during the high rainfall years. In contrast, larvae of B. decoloratus were more numerous during the drier years. A. hebraeum larvae were also more abundant during the drier years. The strong positive correlation of adult R. appendiculatus abundance with rainfall and the coincidence of increased adult tick challenge with increased rainfall indicates that adult R. appendiculatus tick burden on hosts would be heaviest during the wet season and high rainfall years.     

Seedling ecology of two miombo woodland trees

The development of seedlings of two miombo trees, Brachystegia spiciformis Benth. and Julbernardia paniculata (Benth.) Troupin, was studied during two growing seasons (December 1989–April 1991) at a Zambian grassland site. Seed germination rates under laboratory and field conditions were not significantly different although germination in the field was delayed by 1–2 weeks due to insufficient rainfall. After one year of storage J. paniculata seed germination had declined from 67% to 17% while germination of B. spiciformis seeds remained at about 83%.Leaf production was confined to the rainy season. Leaf fall occurred during the dry season and in J. paniculata this was followed by shoot die-back during the hot dry period (August–November). Two-thirds of B. spiciformis seedlings experienced shoot die-back but shoot die-back did not necessarily result in seedling mortality. Seedling deaths occurred during the germination period (6–10 weeks after planting) and in the hot dry period (40–50 weeks after planting) during September–November. Survivorship of B. spiciformis seedlings was 74% at the end of the second growing season while this was 46% for J. paniculata.Shoot growth was negligible during the second growing season. In fact mean maximum leaf area of B. spiciformis decreased significantly from 19.7 cm² (SD=5.7) per plant at the end of the first growing season to 13.3 cm² (SD=5.8) at the end of the second growing season (t=3.31, P<0.01). However, root biomass of B. spiciformis seedlings increased 2.8 times during the second growing season.These results suggest that shoot die-back in seedlings of miombo trees is caused by drought and that the slow shoot growth is the result of allocating most of the biomass to root growth during seedling development.     

Phosphorus inputs to Lake Naivasha,Kenya, from its catchment and the trophic state of the lake

The main river supplying Lake Naivasha, Kenya, the Malewa, drains a catchment given over to largely subsistence cultivation and animal husbandry. The lake itself is the focus for an intensive horticultural industry based upon irrigation from the lake. The Malewa, however, is relatively independent of the impact of industry, and so its contribution to eutrophication of the lake was evaluated. Two periods of study, a very wet-dry and a `normal' wet-dry season showed that the river contribution of phosphorus led to a total phosphorus loading of 1.4 g m<sup>–2</sup> lake surface ann<sup>–1</sup> in the very wet period compared to 0.2 in the `normal'. Chlorophyll `a' in the open water of the lake was significantly related to soluble reactive phosphorus. The lake is now eutrophic by normal limnological criteria.     

Seasonal and environmental effects on the blood hemoglobin concentrations of some Panamanian air-breathing fishes

Synopsis Interspecific differences in blood hemoglobin concentration ([Hb]) occur among air breathing fishes. However, the effect on [Hb] of factors such as air-breathing organ structure and blood circulation pattern, air breathing behavior, as well as season and environmental conditions have not been fully examined. [Hb] in seven Panamanian species of air-breathing freshwater teleost fishes were compared and were monitored for most species during the wet and dry seasons and in hypoxic laboratory conditions. Fishes studied were Ancistrus, Hypostomus, and Loricaria (Family Loricariidae); Hoplosternum (Callichthyidae); Synbranchus (Synbranchidae); Piabucina (Lebiasinidae); and Dormitator (Eleotridae). [Hb] in these species ranged from 4.8 to 14.6 g 100 ml^–1 (g%). Ancistrus, Hypostomus, and Dormitator significantly increased [Hb] during the dry season and, with Piabucina, also increased [Hb] when acclimated to hypoxia in the laboratory. An increase in [Hb] during the dry season may precondition facultative air breathers for habitat hypoxia (and the need to respire aerially) in the event this occurs. Intraspecific differences in both [Hb] and in red cell Hb-phosphate ratio, an index of oxygen affinity, were found in populations of Hypostomus and relate directly to differences in habitat oxygen level. In all species tested alterations in blood hematocrit (Hmct) and mean corpuscular hemoglobin concentration (MCHC) occurred only with correspondingly large net changes in blood [Hb]. The [Hb] of Loricaria, Synbranchus, and Hoplosternum was not affected by season or hypoxia and this may be due to behavioral and physiological adaptations that reduce the transbranchial loss of aerially-obtained oxygen or to a ventilatory mode that precludes this possibility.     

Phylogenetic relationships among genera in theLiliaceae-Asparagoideae-Polygonatae s.l. inferred fromrbcL gene sequence data

The chloroplast gene encoding ribulose-1,5-bisphosphate-carboxylase (rbcL) was sequenced for phylogenetic analysis of 13 species (10 genera) in the tribePolygonatae s.l. of theLiliaceae-Asparagoideae. The data were analysed using maximum parsimony and neighbour-joining methods. There were 233 phylogenetically informative sites out of 1368 base pairs compared. The results suggest that there are three monophyletic groups withinPolygonatae s.l. with high bootstrap confidence values. Group A representsPolygonatae s.str., with generaMaianthemum, Smilacina, Convallaria, Disporopsis, andPolygonatum. Group B containsUvularia andDisporum and group C includesStreptopus, Tricyrtis, Clintonia, andProsartes. The study suggests thatPolygonatae s.l. are not a monophyletic group, including at least three groups of different phylogenetic origin. Monophyly of the taxa within groups A, B, and C is supported by the high bootstrap confidence values (85–100%) of the bootstrap replications for both parsimony and neighbour-joining methods. The differences between each group (calculated as 100x base substitutions per site) were 6.99–9.03 for group A and B, 4.92–7.35 for A and C, and 6.66–7.57 for B and C.     

Aspects of the population dynamics of Neosarmatium meinerti at Mgazana, a warm temperate mangrove swamp in the East Cape, South Africa, investigated using an indirect method

Encysted embryos (cysts) of the brine shrimp, Artemia provide an excellent model system for the study of biochemical adaptation to environmental extremes. Here, we describe an experiment in which cysts of A. franciscana from the San Francisco Bay (SFB), California, U.S.A., were inoculated into experimental ponds in the Mekong Delta region of Vietnam where water temperatures are much higher than the SFB. Cysts produced in each of three successive growing seasons (1996–1998) were collected and examined in the laboratory for resistance to high temperature and relative contents of three stress proteins (Hsp-70, artemin and p26). Thermal adaptation took place rapidly, during the first growing season. The increase in thermal tolerance was reflected in an overall increase in stress protein content, compared to SFB cysts used for the initial inoculation. Also examined were cysts of A. tibetiana collected from a lake on the high plateau of Tibet, PR China, almost 4.5 km above sea level. These cysts were very sensitive to high temperatures, and contained much lower levels of all stress proteins examined, compared to A. franciscana cysts from SFB and Vietnam. Cysts of A. sinica, collected from a hypersaline lake in Inner Mongolia, PR China, were examined in the same fashion and found to be similar to SFB cysts in terms of thermal resistance and stress protein content. The harsh environments in which Artemia are found, and the great diversity of its habitats, world-wide, provide excellent opportunities to relate the ecological setting of an organism to the underlying physiological and biochemical processes enabling its survival.     

Life history,resting egg formation,and hatching may explain the temporal-geographical distribution ofArtemia strains in the Mediterranean basin

Life history traits are presented for the sexual species (Artemia tunisiana) and for parthenogenetic diploid and tetraploid strainsA. parthenogenetica reared at 15 °, 24 ° and 29.5 °C.In laboratory cultures, we present evidence that the seasonal appearance of the sexualArtemia tunisiana (the dominant winter-spring population), and of two parthenogenetic populations ofArtemia (the dominant spring-summer populations) in certain Spanish saltworks is controlled by temperature through its effect on reproductive and survival traits. Minimum and maximum reproductive output and survival for the sexual and parthenogenetic populations, respectively, occurred at a typical temperature (24 °C) of the late-spring season when the sexual population is replaced by parthenogenetic forms. Furthermore, the high production and hatchability of cysts from the sexual population at low temperatures (15 °C), and of the parthenogenetic populations at middle temperature (24 °C), indicate the role of dormancy as an adaptation regulating seasonal occurrence.     

Elephant dung decomposition and coprophilous fungi in two habitats of semi-arid Botswana

In order to understand the impact of habitat changes on ecosystem processes caused by increased populations of elephants, elephant dung decomposition was studied in semi-arid Botswana. Dung decomposition rates were studied with and without the presence of arthropods, using pairs of exposed dung and dung enclosed in nylon-mesh bags, respectively. Dung decomposition rates were lower in the absence of arthropods. The rates in the late wet season were higher in the scrubland than in the woodland. In the early dry season, immediately after the wet season, the rates were higher in the woodland than in the scrubland. The difference in decomposition rates between habitats was attributed to microclimatic conditions created by vegetation cover. With regard to fungal succession, Cladosporium cladosporioides and Eurotium brefeldianum occurred only in the late stages of dung decomposition whereas Talaromyces helicus, Cercophora coprophila and Sporormiella minima occurred in all the stages. Although there was no significant difference in Shannon–Weiner fungal species diversity index between habitats, seasons, dung ages and laboratory incubation periods, there were significant differences in fungal community composition between these parameters. Species richness was higher in the late wet season than in the early dry season, indicating the importance of moist conditions for a large diversity of fungal species.     

Population dynamics of Potamothrix alatus paravanicus Poddubnaya & Pataridze (Tubificidae) in different areas of Lake Sevan

Potamothrix alatus paravanicus Poddubnaya & Pataridze (Tubificidae) is the most abundant species of benthic invertebrate in Lake Sevan and the only species in the deep profundal. Differences in annual temperature, length of the stratification period (low oxygen content) and bottom sediment characteristics influence the population of P. a. paravanicus in different depth zones of Lake Sevan. From shallow to deep water a regular increase of the following indices was observed in 1984–1987: annual biomass from 1.2–2.0 to 8.2–17.0 g m^–2 wet weight; mean individual wet weight of clitellate specimens from 2.0–3.8 to 8.3–16.6 mg; total life span from one and a half to more than 20 years; the length of breeding season from 2–3 to 12 months.An important ecological distinction between P. a. paravanicus and allied Potamothrix hammoniensis (Michaelsen) is the much lower fecundity of the former species.