Observations on the life cycles of aquatic Oligochaeta in aquaria

Observations on the life cycles of aquatic oligochaetes were made in the period 1962–2017 at the Võrtsjärv Limnological Station (Estonia) using small aquaria with sieved profundal mud covered with unaerated water. The aquaria were mostly inseminated with 10 juvenile worms and checked four times a year, changing the mud and eliminating the progeny, until the natural death of the original worms. Besides, mass cultures were kept in bigger aquaria. Many individuals of Tubifex tubifex, T. newaensis, Limnodrilus hoffmeisteri, L. udekemianus, Ilyodrilus templetoni, Psammoryctides barbatus, Spirosperma ferox, Potamothrix moldaviensis, P. vejdovskyi, P. bavaricus, Stylodrilus heringianus and Rhynchelmis tetratheca survived for several years, reproduced repeatedly, and died out one by one during the observation period. In some cases, the most longevous individuals reached an age of up to 8 years (I. templetoni), 10–12 years (T. tubifex), 15–17 years (L. hoffmeisteri, P. barbatus, S. heringianus), or even more than 20 years (L. udekemianus, S. ferox, T. newaensis). Criodrilus lacuum did not reproduce in aquaria, although the oldest individual spent 46 years there. Potamothrix hammoniensis, Lophochaeta ignota, Lamprodrilus isoporus, most naidines and some others did not thrive in aquaria and usually died without reproducing. In a cellar, where temperature conditions imitated seasonal fluctuations in lakes, or when the aquaria were maintained at continuously low temperature, the lifetime of worms was often longer than at room temperature. At elevated temperatures (+25° to +35°C) T. tubifex and L. hoffmeisteri formed cocoons mostly with only 1–2 eggs while their life span was then shorter. Architomic clones of Potamothrix bedoti, Bothrioneurum vejdovskyanum, Aulodrilus pluriseta and A. japonicus survived and propagated for years. The architomic Lumbriculus variegatus was thriving only when fed, e.g., with yeast. Uniparental reproduction by parthenogenesis was observed in T. tubifex, L. hoffmeisteri and S. heringianus kept or reared single. Two special races(?) were noted both within T. tubifex and L. udekemianus.

Impact of secondary salinisation on the structure and diversity of oligochaete communities

Secondary salinisation has become one of the most important factors responsible for changes in the aquatic biota. Earlier research has focused on macroinvertebrates including oligochaetes in anthropogenically saline rivers and streams, but studies on oligochaetes in anthropogenically saline stagnant waters remain scarce. Therefore, this study was conducted to assess changes in the species composition as well as the abundance and biomass of oligochaete communities along a large salinity gradient in the anthropogenic inland water bodies located in the Upper Silesian Coal Basin (Southern Poland), which is one of the largest coal basins in Europe. Herein, a total of 27 oligochaete species including five alien species were assessed, namely, Potamothrix bavaricus, Potamothrix hammoniensis, Potamothrix moldaviensis, Psammoryctides albicola, and Psammoryctides barbatus. The results confirmed that the freshwater oligochaetes could tolerate elevated water salinity and showed highest densities and taxa richness in intermediate salinity. Moreover, the waters with the highest salinity had an extremely low number of oligochaete species. A salinity level above 2800 mg L−1 led to significant loss of diversity of the oligochaetes, and consequently, these habitats were colonized by halotolerant species, especially Paranais litoralis, whose abundance increased with increasing salinity gradient.

Reproduction of Potamothrix hammoniensis (Oligochaeta) in shallow eutrophic lakes

The aim of the study was to indicate the abiotic parameters of water and bottom sediments, which significantly affect the reproduction of Potamothrix hammoniensis in 9 shallow eutrophic lakes, of which 5 were dominated by macrophytes and 4 – by phytoplankton. Samples were collected once a month from January to December 2012. The percentage of Potamothrix hammoniensis individuals with a developed reproductive system varied in individual lakes and ranged from 14 to 72%. There was no correlation between the distinguished lake types and the proportion of sexually mature individuals. The reproductive activity was not observed in summer and early autumn. Among the measured parameters, the highest values of the Pearson correlation coefficient were found between the percentage of individuals with a developed reproductive system and the conductivity (r = 0.69; p < 0.001), pH (r = 0.51; p = 0.002) and the organic matter content in the sediments (r = −0.42; p = 0.012). It is worth noting that there was no correlation between the percentage of sexually mature specimens and the water temperature (r = −0.22, p = 0.204) and the oxygen concentration (r = −0.08; p = 0.648).

Water residence time in the Włocławek dam reservoir (the Vistula river, Poland) affects its macrozoobenthos structure

The aim of our study was to compare the macrozoobenthos structure as well as water and organic matter content of the bottom sediments of two hydrologically different zones of a strongly fluvial the Włocławek Dam Reservoir. Samples were collected from the Włocławek Dam Resevoir at six sites. Three of them were located in the upper, rheolimnic part (URP) of the reservoir and three others in its lower, limnetic part (LLP). Water transparency, sediment water content and organic matter content in the sediments were higher in the LLP. The higher number of taxa and diversity of macrozoobenthos were found in the URP of the reservoir. The density of bottom fauna was slightly higher in the LLP (90,990 ind. m−2) than in the UPR (73,486 ind. m−2), while the significantly higher biomass of macrozoobenthos was found in the URP of the reservoir (2314 g · m−2) than in the LLP (336 g · m−2). The dominant taxa of Oligochaeta and Chironomidae larvae did not show significant differences in the density between both zones. Some taxa were found only in the URP. In this zone, significantly higher densities of other taxa were observed. The only species with greater abundance in the LLP was Potamothrix hammoniensis (Oligochaeta). Due to the very short water residence time, the differences in the parameters under study between the URP and the LLP of the reservoir were smaller as well as the abundance of the macrozoobenthos was distinctly higher than in other reservoirs.

Metal Contents in Water, Sediment, and Oligochaeta-Chironomidae of Lake Uluabat, a Ramsar Site of Turkey*

Samples of lake water and sediment, and sediment and two dominant zoobenthic taxa (Oligochaeta:Potamothrix hammoniensisand Chironomidae:Chironomus[Camptochironomus] tentans larvae), were collected from 12 stations in Lake Uluabat and examined from the metal level point of view (cadmium, chromium, lead, copper, nickel, and zinc). Our results showed that the occurence of metals in water, sediment, and the two zoobenthic taxa are relatively high. The opinion that supports the results of Lake Uluabat shows that certain species of oligochaetes and chironomids accumulate examined metals several times over compared to their surroundings. Therefore, it is concluded that the oligochaetes and the chironomids are suitable candidates to be used in biomonitoring surveys of Lake Uluabat.