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.     

Damage released prey alarm substances or predator odours? Risk assessment by an aquatic oligochaete

Although the abilities of prey to detect and respond to chemical substances associated with a predator have been widely reported, the factors promoting the evolution of responses to prey alarm cues vs. predator odours are still vague. In this article, we combined field research with laboratory experiments to explore which chemical substance associated with predator activity (predator odour, conspecific or heterospecific alarm substances) induces defence responses in the aquatic oligochaete Stylaria lacustris, which is vulnerable to common littoral predators. The field results indicated that predators injure the oligochaetes and a great proportion, up to 45% of individuals in the population, were found to be damaged. The results of the laboratory experiments revealed that chemical odours from damselfly larvae feeding on S. lacustris did not induce the defence response in the oligochaetes. On the contrary, oligochaetes detected and responded to alarm substances from damaged conspecifics alone and substances from damaged cladoceran Daphnia magna. We discussed conditions favouring the responses to damage released prey alarm cues instead of predator odours in Stylaria lacustris. Our data suggest that the selection of responses to alarm cues from damaged prey vs. predator odours may be dependent on three factors: (1) non-species-specific predation, (2) divergence of food niche of the different stages of the predator and (3) complex food web with multiple predators. Handling editor: S. Declerk     

Diversity and distribution of Tubificidae, Naididae, and Lumbriculidae (Annelida: Oligochaeta) in the Netherlands: an evaluation of twenty years of monitoring data

Data from 24 water management districts and the rivers Rhine and Meuse in the Netherlands were used to study geographical distribution, relative occurrence, and environmental requirements of 76 aquatic oligochaetes (families Tubificidae, Naididae, and Lumbriculidae) (Annelida, Clitellata). Approximately 50% of the 76 species that occur in the Netherlands are uncommon, rare, or very rare. The other half of the species are common, very common or abundant. The abundant species are: Stylaria lacustris, Ophidonais serpentina, Limnodrilus claparedeianus, Limnodrilus hoffmeisteri, and Lumbriculus variegatus. With the exception of several brackish water species (those restricted in distribution to water management districts close to the sea that are influenced by salt water influx) and specific running water species (restricted mainly to the eastern part of the Netherlands), most of the species occurred throughout the whole Netherlands. The species distribution was related to environmental variables using ordination. In general, species distribution was correlated with either large waters with high chloride and phosphorus concentrations and a high hydrogen ion concentration (as pH), or with small forested (running) waters in more natural (undeveloped) areas that occasionally become intermittent. Vegetation cover was positively correlated with several swimming species in the family Naididae. While the distribution of aquatic oligochaetes in some families occurring in the Netherlands is known to some extent, the occurrence and distribution of rare and small taxa, particularly those that are difficult to identify taxonomically, is virtually unknown. Some of the rare oligochaete taxa, especially those associated with unique habitats, have received only cursory attention. Also in the data studied, the observations of the more rare species were too few to draw conclusions. To improve our knowledge of oligochaete distribution in the Netherlands, additional research should focus on rare species associated with special habitats and water types (natural areas) and those taxa in poorly known families. The standardisation of sampling and processing methodologies, particularly the use of nets and sieves with fine-meshed screening, will ensure the collection of the smaller species of oligochaetes. Subsequently, oligochaetes should be identified to species level by experienced taxonomists trained in oligochaete identification. Finally, many aquatic oligochaete species are identifiable only when sexually mature and therefore the time of year in which samples are collected is critical to the accurate representation of true oligochaete diversity at any given site. For analysing the relation between species and environmental variables the best option is to use composite data from spring and autumn.     

Environmental factors affecting the distribution and abundance of cyst-forming Myxobolus spp. and their cyprinid hosts in 3 lakes in Algonquin Park,Ontario

In 1999, 4 species of cyprinid were surveyed for myxozoan parasites in a watershed in Algonquin Park, Canada, Kathlyn Lake. Broadwing Lake, and Lake Sasajewun were included. Eight species of Myxobolus were found that differed in their prevalence and distribution among the 3 lakes. The oligochaetes and environmental parameters, including sediment types and aquatic plants, of these 3 lakes were surveyed the following year. Oligochaetes belonging to 17 species were collected from the 3 lakes. The distribution patterns of the oligochaete fauna, with respect to the environmental variables, were examined using canonical correspondence analysis. Naidids were predominant in all 3 lakes, particularly in the pebbly and sandy sediment of Lake Sasajewun. The highest percentage of tubificids occurred in the detritus and muddy substrate of Broadwing Lake. These findings indicate that the prevalence of certain oligochaetes is congruent with the absence or presence of particular myxozoan species and that substrates and aquatic plants influence the distribution of certain oligochaete species.     

A cross-phyla response to Daphnia chemical alarm substances by an aquatic oligochaete

Although chemical alarm substances from damaged heterospecifics have been well documented to induce defense mechanisms in potential prey, data about antipredator responses to alarm cues from prey organisms of a distinct phylum are scarce. In this study, we analyze the response of an oligochaete to chemical alarm substances from distantly related cladocerans. We conducted laboratory experiments to investigate whether the aquatic oligochaete Stylaria lacustris detects and responds to alarm substances from Daphnia. The oligochaetes were exposed to alarm substances from Daphnia magna, which is a member of the same prey guild, and D. hyalina, which is vulnerable to different predators. S. lacustris increased the fission rate in response to cues from conspecifics and the heterospecific D. magna. These species share common predators, especially damselfly larvae and hydras. In contrast, chemical cues released from D. hyalina did not induce an increase in the reproductive rate of the oligochaetes. D. hyalina is a pelagic species and is not included in the diet of predators preying upon S. lacustris. Our results indicate cross-phyla responses among invertebrates (Annelida and Arthropoda), and suggest strong selection pressures to respond to heterospecific alarm substances. The oligochaete S. lacustris is able to differentiate chemical substances released from damaged Daphnia of two different species. These results show that alarm cues released from damaged Daphnia may be species-specific. However, further studies on the chemical structure of alarm substances in cladocerans are needed to support this hypothesis.     

New records of aquatic Oligochaeta from Texas,with observations on their ecological characteristics

Twenty-six species of aquatic oligochaetes are reported from Texas, including 18 Naididae, seven Tubificidae, and one Glossoscolecidae. Illustrations are provided for ten species recorded for the first time from the state: Chaetogaster cristallinus, Nais elinguis, Nais pardalis, Pristina acuminata, Pristina sima, Stylaria lacustris, Aulodrilus limnobius, Ilyodrilus templetoni, Limnodrilus claparedianus, and Sparganophilus tamesis. Species accounts include presently known distributions in Texas and ecological and morphological characteristics.     

Oligochaeta and Aphanoneura in ancient lakes: a review

By their antiquity, history, rarity, great depth in many instances and the presence of highly diverse faunas with many endemics, ancient lakes constitute ecosystems of a special nature, clearly apart from the large majority of extant lakes. While the fauna of these lakes is becoming better and better known for various animals groups, the Oligochaeta are still poorly known. Tubificidae and Naididae are found in each ancient lake. On the other hand, some families are restricted to only one lake, such as Aeolosomatidae and Proppapidae in Lake Baikal or Eudrilidae and Ocnerodrilidae (megadriles) in Lake Tanganyika, but such a distribution is probably due to a lack of knowledge or sampling biases. All ancient lakes have an endemic oligochaete fauna except Lake Kinneret (Israël). The oldest, Lake Baikal (20–25 Ma), holds the most abundant and diverse oligochaete fauna, in which species flocks are even recognizable or suspected. In contrast, the oligochaete fauna of the slightly younger Lake Tanganyika is very scarce. This is partly due to an obvious lack of studies, as the oligochaete fauna of other great African lakes is virtually unknown, but this might be the result of an environment in these lakes less favourable to oligochaetes. Some factors likely to interact with speciation in oligochaetes are discussed but nothing can be concluded to date. A recent interest in African great lakes revealed a more diverse oligochaete fauna than previously assumed but a better study of this fauna is still badly needed.     

An experimental system to study ecophysiological responses of submerged macrophytes to temperature and light

An experimental growth system was devised to study the ecophysiological responses of submerged macrophytes to temperature and light. Using the system, a pilot study was conducted to compare responses to light of three representative species common to the littoral zone of Lake Biwa: Vallisneria asiatica Miki var. biwaensis Miki, which is endemic to Japan, Potamogeton maackianus A. Benn., a dominant submerged macrophyte in Lake Biwa, and Elodea nuttallii (Planch.) St. John, one of the most influential submerged exotic macrophytes naturalized in Japan. Different relative growth rate responses and other growth parameters among the species were observed. We ascertained the experimental system to be useful for the comparison of ecophysiological responses of submerged macrophytes.     

Distribution and ecology of Middle Atlantic Bight Oligochaeta

Distribution and ecology of continental shelf oligochaetes are poorly understood. From 1975 through 1977 baseline ecological studies were conducted in the Middle Atlantic Bight prior to oil exploration activities. A total of 38 species in three oligochaete families were collected. Of this total one family and 29 of the species were undescribed at the time of collection. The most abundant and widely distributed species were Limnodriloides monothecus, L. medioporus, Bathydrilus longus, Phallodrilus biprostatus, and Tubificoides diazi. No single species dominated the oligochaete fauna. All the oligochaete species responded to changes in physical parameters over the shelf similarly to the total macrofauna. Seasonal trends within the oligochaetes were not found. Species that preferred coarser sand sediments were all small interstitial forms. The finer sand and eurytopic species were all burrowers. Zoogeographically the Middle Atlantic Bight oligochaetes were predominantly temperate (16 species) with some southern species (8). Seven species were broadly distributed from the Caribbean to Massachusetts or around the world. Seven species were only known from the area studied.Contribution No. 1397 of the Virginia Institute of Marine Science.     

The effect of organic pollution on the abundance and distribution of aquatic oligochaetes in an urban water basin, Taiwan

Aquatic oligochaetes are abundant in polluted areas and are, therefore, commonly used as bioindicators to study organic pollution in rivers and streams. In order to develop a species-level oligochaete biotic index to reflect the River Pollution Index (RPI) in the Taichung Water Basin in Taiwan, we conducted a systematic sampling scheme to collect aquatic oligochaetes from the sediment samples of watercourses in the Taichung Water Basin, Taiwan. We evaluated the relationships between aquatic oligochaetes and the sewage pollution using statistical methods. The distribution of aquatic oligochaetes in relation to environmental variables, such as water quality and sediment characteristics of the regional urban contaminated streams was expressed by Canonical Correspondence Analysis (CCA). We identified 17 species of aquatic oligochaetes (Annelida, Clitellata) including 3 species of Tubificidae, 13 species of Naididae, and 1 species of Enchytraeidae from the watercourses of an urban region in the Taichung Water Basin in Taiwan, during the summer and winter of 2005 and 2006. A positive correlation was found between the total abundance of aquatic oligochaetes and the RPI (r = 0.58, P < 0.05). However, only population density of the most abundant tubificid, Limnodrilus hoffmeisteri, increased with increasing RPI values and a significantly negative correlation was found between the population density of the naidid, Nais communis, and RPI values. The results of CCA indicated that certain naidids, such as Aulophorus furcatus and Allonais gwaliorensis also tolerated extremely polluted environments in upper stream or stony habitats, implying that tubificids should not be the sole representation of simple biotic indices but should also include pollution-tolerant naidids. We found that the community structure of aquatic oligochaetes was influenced by short-term variations in microhabitat rather than according to seasonal factors in our study region. The results proved that aquatic oligochaetes were sensitive enough to provide a supplement for the regional urban pollution assessment applications for biotic indicators at the species-level.     

Structure and dynamics of zooplankton communities in the littoral zone of some North Carolina lakes

Species composition and seasonal, dynamics of zooplankton in the littoral zone were studied in three piedmont North Carolina lakes for one year. Nygaard's compound index indicated oligotrophic conditions in Belews Lake and eutrophic conditions in Salem Lake and Lake 150. A total of 32 species of zooplankton were found in the samples. Significantly fewer species of truely littoral zooplankton were present in the oligotrophic lake regardless of season (P < 0.05). Eutrophication appears to favor increased diversity in zooplankton of the littoral zone. Habitat heterogeneity, provided by a well developed littoral zone containing aquatic macrophytes, may be the major factor contributing to the maintenance of more taxa of zooplankton in eutrophic systems.Distinct taxa of Cladocera and Copepoda are present in the littoral zone, exhibiting seasonal dynamics that are largely different from the limnetic fauna. Such dynamics may result from predation by characteristically limnetic species of cyclopoid copepods which seek prey in the littoral zone. The numerical and seasonal abundance of predators and prey are inversely related and the true littoral taxa, represented in the present study by the genera Alona, Chydorus, Pleuroxus, Sida, Simocephalus, and Eucyclops, contained no predaceous species. The seasonal dynamics of these genera are very similar even in widely separated geographical regions, indicating that the factor(s) responsible operate independently of climatic and chemical variables. Intrazooplankton predation appears to be a more plausable explanation than segregation along depth which, although consistent with data from studies of limnetic waters, cannot be related to populations of zooplankton in shallow littoral areas.     

Mitochondrial phylogeny reveals the artificial introduction of the pale chub Zacco platypus (Cyprinidae) in Taiwan

The presence of the pale chub Zacco platypus (Japanese name, Oikawa) in Taiwan has been suggested to be a result of its inadvertent introduction from Lake Biwa in Japan in the 1980s in conjunction with the Japanese Ayu, Plecoglossus altivelis altivelis, which was released several times into the Tamsui River to restock the extinct Ayu population of Taiwan. However, it is also possible that Z. platypus is native to Taiwan and has not been previously described for reasons of its narrow range. Knowledge of the colonizing history of Z. platypus is of considerable importance because it provides insight into the evolutionary process and, hence, impacts management decisions regarding this species in Taiwan. A portion of the mitochondrial D-loop was sequenced for 77 specimens from five populations of Z. platypus from Japan and Taiwan. A total of 22 haplotypes were identified, and nucleotide divergence among haplotypes ranged from 0.20% to 2.82%. Haplotype diversity was high in all populations examined, with a range from 0.718 in the Tagiri River population to 0.909 in the Lake Biwa population. Phylogenetic and statistical parsimony analyses of the molecular data revealed a close genetic relationship between Taiwanese and Japanese Z. platypus and supported the previous report that the Taiwanese Z. platypus originated in Lake Biwa in Japan.     

Occurrence of the endangered species Nitellopsis obtusa (Charales,Charophyceae) in western Japan and the genetic differences within and among Japanese populations

Nitellopsis obtusa (Charales, Charophyceae) are widely distributed from Europe to Asia; however, this species has been recorded in only the five lakes in central Honshu in Japan. This species was thought to be extinct in Japan, but was rediscovered in limited areas of Lake Kawaguchi in central Honshu. More recently, we discovered more Japanese populations of N. obtusa in Lake Biwa in western Honshu, and it became clear that the species had a broader distribution in Japan than originally believed. In addition, although only male or female thalli have been collected at each lake, both male and female thalli were found from Lake Biwa. This is the first report of a potentially sexual population of N. obtusa in Japan. The DNA sequences of three chloroplast DNA markers, including both coding and non‐coding regions, were identical in all specimens from Lake Kawaguchi and Lake Nojiri (Central Honshu), and differed from those of Lake Biwa and German specimens. Although Japanese and German specimens were genetically similar, Japanese specimens displayed considerable genetic diversity according to locality.     

The bottom Oligochaeta communities in sand pits of different trophic status in Upper Silesia (Southern Poland)

Oligochaeta, occurring in the littoral zones of two sand pits, were sampled in order to determine the relationship between the oligochaete species and the waters’ trophic level. Differences between sand pits attributable to community structure and to an overall higher abundance of oligochaetes, especially tubificids, were observed in Dzierżno Małe. Multivariate analyses (correspondence analysis [CA] and canonical correspondence analysis [CCA]) reveal correlations between the distribution patterns of oligochaete species and the concentration of nitrates, phosphates and dissolved oxygen. Some species, e.g. Dero digitata, Limnodrilus hoffmeisteri, Potamothrix hammoniensis, Nais simplex, Limnodrilus claparedeanus, Limnodrilus udekemianus and Tubifex tubifex, were more abundant in eutrophic sites. The results of the study showed that the richness of Oligochaeta species is not a good method for estimating the trophic levels of the studied sand pits. Indicators based on the share of oligo-, meso- and eutrophic species in Oligochaeta communities are better for evaluating the water quality in the studied reservoirs.     

Lake Superior: an invasion coldspot?

Lake Superior receives a disproportionate number of ballast water discharges from transoceanic ships operating on the Laurentian Great Lakes. Although this provides dispersal opportunities for nonindigenous species (NIS), relatively few NIS were initially discovered in this lake prior to being recorded elsewhere in the basin. A lack of NIS records from this lake may be an artefact of sampling bias. We tested this hypothesis by sampling benthos and plankton from littoral and deepwater habitats around the perimeter of Lake Superior during June and August 2001. Using morphological analysis techniques, we identified a total of 230 invertebrate taxa representing planktonic, benthic and nektonic lifestyles. Five species with invasion histories in the lower Great Lakes, the bivalves Sphaerium corneum, Pisidium amnicum and P. moitessierianum, gastropod Potamopyrgus antipodarum and amphipod Echinogammarus ischnus, were identified for the first time in Lake Superior. In addition, records of expanded distributions within this lake are presented for the amphipod Gammarus fasciatus and oligochaetes Ripistes parasita and Vejdovskyella intermedia. Recently introduced NIS in Lake Superior were found near international ports, implicating shipping as the vector of their introduction. Intrinsic physical-chemical aspects of Lake Superior may account for the scarcity of NIS in this lake as compared to the lower Great Lakes.     

Disappearance of deep profundal zoobenthos in Lake Ikeda, southern Kyushu, Japan, with relation to recent environmental changes in the lake

A benthological survey in a deep caldera, Lake Ikeda, southern Kyushu, Japan, in 1998 revealed that no zoobenthos were found in the deep profundal, although two tubificid oligochaetes, Tubifex tubifex and Limnodrilus hoffmeisteri, and a chironomid, Procladius sp., were distributed in the upper profundal zone. This is the first record of oligochaete composition in the lake. Lake Ikeda had been typically oligotrophic until the 1940s, and zoobenthic assemblages were recorded throughout the profundal bottom in the 1920s and 1970s. Recent disappearance of the deep profundal zoobenthos could be caused by the stagnation of anoxic waters in the hypolimnion, in connection with eutrophication triggered by nutrient loading, as well as change in the thermal circulation system presumably caused by global warming.     

Juvenile migration of the exclusively pelagic cyprinid,Gnathopogon caerulescens (Honmoroko) in Lake Biwa,Central Japan

Migration of wild and cultivated juvenile honmoroko Gnathopogon caerulescens of from the spawning and nursery areas in Lake Biwa were investigated, both in the Ibanaiko Lagoon and its outlet to Daido River, using beam‐trawl surveys in 2013 and 2014. The study demonstrated migration of G. caerulescens from a nursery lagoon toward Lake Biwa after the juvenile stage. These findings appear to be the first direct evidence for migration of an exclusively pelagic cyprinid species from a littoral nursery to a pelagic adult habitat in a large deep lake.     

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.     

Temporal and spatial distribution of chironomid larvae and oligochaetes in two Dutch storage reservoirs

Long-term changes in distribution and taxonomic composition of chironomid larvae and oligochaetes in two water storage reservoirs in The Netherlands were studied. A succession among the chironomid species was observed. In the last 10–15 years chironomid densities varied. Compared with other lakes chironomid densities were high. Densities of chironomids were higher in the littoral zone than in the profundal zone. The opposite was found for oligochaetes. Densities and composition of the chironomid fauna in the two reservoirs were similar.Procladius, Tanytarsus andHarnischia dominated at all depths. However, pupal exuviae samples showed some differences in chironomid taxonomic composition between the two reservoirs. Orthocladiinae, rarely found in bottom samples, abounded in pupal exuviae samples.     

The role of oligochaetes in the management of waters

To better understand the role of an aquatic oligochaete in the management of water quality, it was determined if oligochaetes were representative of water quality, if indices based on oligochaetes were widely applicable to access water quality, and if oligochaete assemblages were related to environmental factors other than organic pollution. It was found that if only one monitoring sample a year was taken in December, about 73% of the more common species were collected. Seasonality did not seem to affect the taxa collected except for forms in low presence, e.g., Nais. Several indices we used were not applicable to regulated streams. Oligochaete ordination procedures revealed only a partial picture of the environmental conditions of regulated streams.