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Presentation at the 11th International Shallow Lakes Conference, Estonia 11.-16.06.2023. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963, by Estonian Ministry of the Environment through the state monitoring programme, and also from the Estonian Research Council grant PRG1167. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963, by Estonian Ministry of the Environment through the state monitoring programme, and also from the Estonian Research Council grant PRG1167.

Cladocerans have been shown to exhibit a variety of responses to chemical stimuli associated with predation risk, including those from predators and injured conspecifics. In this study, we tested the hypothesis that individuals of Chydorus sphaericus would respond with avoidance behavior to chemical cues from both injured conspecifics and injured heterospecifics. Avoidance behavior was seen in response to cues from C. sphaericus and Daphnia magna. Responses to cues from Daphnia pulex were intermediate between those of the other cues and the water control. We propose that a concentration effect may be responsible for the mixed responses to heterospecific cues and speculate that responses to a broad range of cues may help explain the expansive range of C. sphaericus.

Toxicity of perfluorooctanoic acid (PFOA) and triazoles, that is, paclobutrazol (PBZ) and triadimefon (TDF), singly and in binary mixtures was assessed on the benthic cladoceran Chydorus sphaericus. Following single exposure, toxicity of PBZ was not significantly different from that of TDF as shown by the overlapping 95% confidence intervals of their median effective concentrations: EC50(PBZ) = 0.07-0.09 mM; EC50(TDF) = 0.066-0.078 mM. PFOA was far less toxic than these triazoles: EC50(PFOA) = 0.20-0.24 mM. Assuming no interactions between PFOA and the triazoles, the toxicity of PFOA in mixtures with the triazoles estimated by the concentration addition (CA) and independent action (IA) models was significantly lower than its toxicity in single exposure. This contrasted with the results for PBZ and TDF. Based on the assumption that PFOA may interact with the triazoles, different predictions were obtained by the two models. Significant alleviation of PBZ and TDF on the toxicity of PFOA was found by the extended CA model only. According to the extended IA model, PFOA had nonsignificant effects on the toxicity of PBZ while significantly increasing the toxicity of TDF. This difference is possibly related to different modes of actions for various functional groups in PBZ and TDF.

Species diversity, biomass and abundance of zooplankton were studied in the Curonian Lagoon in 2001. The studies revealed that changes in the abundance, biomass and species diversity of zooplankton depended on the sites and time of sampling. Forty-one species of zooplankton was identified from samples collected in the Curonian Lagoon. The zooplankton community was dominated by Chydorus sphaericus and Thermocyclops oithonoides. Shannon-Weaver biodiversity index depended not only on the sites and time of sampling, but also on a particular part of the Curonian Lagoon where the samples were collected.

(2001). Chydorus sphaericus as a biological indicator of water quality in lakes. SIL Proceedings, 1922-2010: Vol. 27, No. 6, pp. 3358-3362.

Since 1991 faunal collections have been made from the mountain lakes of NW Slovenia. These lakes are at altitudes of between 1250 and 2150 m a. s.l., and have rich biotas, both in terms of species-richness, and faunal abundance. Amongst the animals collected were ‘hump-backed’ specimens of genus Chydorus. These are identical with Chydorus ‘mutilus’, a species described from Swiss mountain lakes by Kreis (1921). The abundance of specimen in the collections, coupled with the availability of data from four successive years of sampling, allowed the detailed analysis of these populations. This also includes an examination of chitinous remains preserved in subrecent sediments.

With their global distribution, environmental persistence, and potential risk to human beings and ecosystems, poly- and perfluorinated compounds (PFCs) are of particular concern for research and regulatory communities. However, insufficient toxicity data are available for most poly- and perfluorinated compounds to assess their possible environmental hazards accurately. Therefore, the acute toxicity of seven poly- and perfluorinated carboxylic acids and alcohols on two cladocerans, Daphnia magna and Chydorus sphaericus, was evaluated in the present study. The adverse effects of these PFCs on these two cladocerans decreased with increasing fluorinated carbon chain length (nC) and quantitative structure–activity relationships were developed to quantify this observation. Because the 50% inhibition effects (EC50) values obtained are far above concentrations typically found in surface water, acute harmful effects of these chemicals to D. magna and C. sphaericus are not expected in the real environment. Environ. Toxicol. Chem. 2012;31:605–610. © 2011 SETAC

A small hypertrophic reservoir (Foix Reservoir, Spain) was sampled from March 1997 to January 2000 to document the composition and spatial and temporal variability of the zooplankton assemblage. Twenty five species of Rotifera, 10 of Cladocera, and one species of copepod (Acanthocyclops robustus (Sars)) were collected. The most abundant rotifer species were Brachionus angularis (Gosse) and Polyarthra spp. Daphnia galeata Sars, Ceriodaphnia quadrangula (Müller), and Chydorus sphaericus (Müller) were the main cladocerans. For each species, brief information is given on ecology, distribution, and occurrence in Spain and in the Foix Reservoir. The zooplankton community of the Foix Reservoir was characterized by the abundance of heleoplanktonic species, which accounted for 50 % of the taxa. Remarkable changes over time in species' composition and occurrence were found for Rotifera and Cladocera during the study period. A. robustus showed high density and biomass values throughout the sampling period. In the summer of 1999, copepods avoided deep layers, whereas some Rotifera (Polyarthra spp,, Filinia spp,, Brachionus angularis) and Chydorus sphaericus were found near the anoxic bottom. A rare rotifer in the Iberian Peninsula, Itura aurita aurita (Ehrenberg), was also found in lotic sections of the reservoir. Un embalse pequeño e hipereutrófico (Embalse de Foix, España) fue muestreado desde Marzo de 1997 a Enero de 2000, con el fin de documentar la composición y variabilidad espacial y temporal de la comunidad zooplantónica. Veinticinco especies de rotíferos, 10 de cladóceros y una especie de copépodo (Acanthocyclops robustus (Sars)) fueron recogidos. Las especies de rotíferos más abundantes fueron Brachionus angularis (Gosse) y Polyarthra spp. Daphnia galeata Sars, Ceriodaphnia quadrangula (Müller) y Chydorus sphaericus (Müller) fueron los principales cladóceros. Para cada especie se da breve información sobre su ecología, distribución y ocurrencia en España y en el Embalse de Foix. La comunidad zooplantónica del embalse se caracterizó por una fuerte presencia de especies heleoplantónicas, que supusieron un 50 % de los taxones. Se constataron cambios remarcables en la composición específica y densidades de rotíferos y cladóceros a lo largo del periodo estudiado. Por el contrario, A. robustus mostró densidades y biomasas altas durante todo el periodo. En el verano de 1999 los copépodos evitaron las capas profundas, mientras que algunos rotíferos (Polyarthra spp, Filinia spp, Brachionus angularis) y Chydorus sphaericus fueron encontrados cerca del fondo anóxico. Un rotífero raro en la Península Ibérica, Itura aurita aurita (Erhenberg), fue encontrado en la sección lótica del embalse.

In August of 2002, we surveyed the zooplankton community of an inland saline lake in West Siberia, Russia—Lake Chany. Thirty species were found, including cladocerans, copepods, and rotifers. The dominant cladocerans were Daphnia longispina, Daphnia magna, Ceriodaphnia reticulata, and Chydorus sphaericus; the dominant copepods were the calanoids Eudiaptomus graciloides and Arctodiaptomus salinus.

Most experiments on the effects of pollutants on zooplankton have been done with laboratory-cultured Daphnia species, but relatively few have been based on the naturally-occuring crustaceans. This study deals with cultures of Chydorus sphaericus, a cladoceran from three Quebec lakes (one polluted lake and two nonpolluted lakes), in a comparative toxicity test involving four heavy metals. Experiments were performed according to a static toxicity protocol, using at least five concentrations per test, five replicates per concentration, ten organisms per replicate and 200 ml volumes of metal solutions. The 48-hr EC50 of each individual metal and of the combination of metals were determined for each culture and for different size classes. The overall toxicity trend is : mixture > Hg >> Cu ≥ Cd > Zn. Juveniles appeared to be more sensitive than adults to heavy metals, but the observed differences were not statistically significant. Contrary to expectation, cultures from nonpolluted lakes showed higher EC50 mean values than the strain originating from a polluted lake.

The purpose of this paper is to investigate the effects of pollution on cyclic reproduction of several cladocerans in an extremely sluggish, polluted, stream (Khir River) in Baghdad, the Republic of Iraq. Daphina magna Straus and Moina brachiata (Jurine) have one sexual phase during the year, while Ceriodaphnia riguadi Richard has two. Simocephalus exspinosus (Koch) exhibits one or two sexual phases, depending on the amount of pollution in the habitat. Blood-size of the last-named cladoceran tends to increase with increase in organic enrichment up to a certain level. Alona costata Sars, Pleuroxus denticulatus Birge and Chydorus sphaericus (O. F. Muller) propagate in the stream but never in sufficient numbers for reliable determinations of cyclic reproduction.

Traps of the carnivorous hydrophyte Utricularia vulgaris Linnaeus (Lentibulariaceae) have structures termed antennae and bristles around their trapdoors that increase their rate of entrapment of the substrate-dwelling prey Chydorus sphaericus (Chydoridae, Crustacea). The kind and number of these structures are important in determining capture rate. Experimental data and corresponding behavioral observations support Darwin's hypothesis that antennae and bristles function as a "funnel" leading potential prey toward the trapdoor and their capture by offering the prey a favorable substrate that exploits their natural locomotor and feeding behavior.

1. 1.|Duration of egg development of Chydorus sphaericus differed significantly under four temperature cycles, all of which averaged 20°C. 2. 2.|Duration of development was also significantly different among groups of C. sphaericus collected 9–12 days apart. 3. 3.|The Kaufmann effect adequately explains the observed differences in duration of egg development under the four different temperature cycles. 4. 4.|To predict duration of development in fluctuating temperatures, it is evidently more accurate to use the weighted average rate of development rather than the rate of development at the weighted averaged temperature.

Chydorus biovatus differs from C. sphaericus sens. str. in that the ephippial female carries two resting eggs, for which the brood pouch is expanded dorsally. resulting in a sharp angle in lateral contour near the junction of the head and shell and in the postpore distance being much elongated. The mature male has the pre-anal angle of the postabdomen rounded and the rostrum broadly rounded, both features being much different than in C. sphaericus sens. str. In North America there is a progressive replacement of C. brevilabris-group species in the South to C. sphaericus-group species in the Far North. Production of two resting eggs by Chydorus piger is recorded.

Two readily distinguishable species of Chydorus sphaericus sens. lat. occur in Salmon Lake, Montana, differing from each other in size and shape of rostrum, headpore configuration, frequency of doubling of teeth on the postabdomen, pattern of reticulation of the shell, and morphology of the mature male, especially the postabdomen, postabdominal claws, copulatory hooks, and rostrum. In any such comparisons, individual specimens are not sufficient; populations are needed to sort out morphological characters associated with instar and sex and character's that change with increasing body size. Comparison of population structure and stage of reproduction can be accomplished by a size-frequency distribution and by specific morphological characters that enable the three male instars to be recognized individually. One species, thought at first to be Chydorus herrmanni, is very close to Chydorus sphaericus sens. str. from Denmark. The other taxon with a short, generally blunt labrum, is described as the new species Chydorus brevilabris. Because of morphological diversity among the entities currently listed as Chydorus sphaericus from around the World, it is certain that a complex of species is represented. To facilitate the eventual resolution of this problem, the population in Sjaelso, Sjaelland, Denmark has arbitrarily been selected as the standard of comparison, and from this population a neotype and several allotypes have been designated. Cursory examination of various available populations suggests that C. sphaericus sens. str. and C. brevilabris represent a major dichotomy in the sphaericus complex, each branch consisting of an unknown number of closely-related species. Cautions are voiced against assuming that Chydorus sphaericus is a single cosmopolitan and ubiquitous species.

Two distinct morphotypes of Chydorus sphaericus are recognised in Ireland. A reference collection of scanning electron micrographs of male and female C. sphaericus sens. str. has been compiled. This collection is used to compare the varying morphological features of Danish and Irish material to determine their taxonomic significance. However, no taxonomic decisions can be made about the Irish morphotypes until mature males and ephippial females become available. Comparison of population structures and stages of reproduction are accomplished by size-frequency distribution. This study illustrates the ever increasing value of scanning electron microscopy (SEM) in chydorid taxonomy, where characters such as shell-reticulation features may easily be misinterpreted using only light microscopy.

Chydorus sphaericus, a cladoceran characterized by a wide range of distribution, is often numerous in various water habitats. Its body size is a consequence of environmental characteristics and physiology. The aim of the study focused on the distribution of body size and densities of C. sphaericus in relation to environmental conditions represented by: (i) habitat types (elodeids, helophytes, and the open water); (ii) specific pond types (forest and field); (iii) pond size (surface area); (iv) the presence/lack of fish; and (v) physicochemical factors. Similar to large daphnids, in the case of the examined small water bodies, fish presence was responsible for a reduction of the body size of C. sphaericus in the zone of open water. More abundant crustacean communities and the presence of larger specimens were found among macrophytes, which indicated that aquatic vegetation offered optimal growth conditions as well as an effective refuge against fish predation. These facts reflect the necessity for maintaining a varied mosaic of habitats even in small water bodies such as the examined ponds. We found that not only the abundance of C. sphaericus but also its body size can be used as an bioindicator of environmental conditions as it preferred small and eutrophic ponds, particularly those with complex macrophyte cover (such as elodeids). Furthermore, the abundance pattern of zooplankton dominant species was affected by elodeids and fish presence as well as by the area of the ponds.

Thirty-four species of Cladocera and 18 species of Copepoda were identified in samples taken from 33 cattle ponds, 21 streams, 9 roadside ditches, and 6 sloughs in Lyon County, Kansas, during the period September, 1958, to April, 1959. These species are listed in a check list with annotations of their relative abundance and seasonal occurrence as well as the water temperature and pH ranges of their habitats. Chydorus sphaericus (O.F.M.) was the most frequently collected copepod. Locality data for 4 species of Cladocera and Copepoda not reported previously in Kansas are included. Although a few publications list the Cladocera and Copepoda which are known to occur in certain limited regions or selected habitats of Kansas (Leonard and Ponder 1949, Ratzlaff 1951, and Prophet 1957, 1959), a complete check list of the Cladocera and Copepoda of Kansas has not been published. To one interested in the ecology and distribution of these crustaceans, a check list covering various geographical regions or states is invaluable. However, a check list that would include the Cladocera and Copepoda of an entire state would take many years to prepare. A complete check list of the Kansas species would require many field samples, since there are few recently published records that could serve as a foundation upon which an extensive check list could be built. The present list includes only those species which have been collected in Lyon County, which is a part of the Arkansas River system draining the southern half of Kansas. It is based on 69 separate field collections taken throughout Lyon County by the authors during the period September, 1958, to April, 1959, and upon published and unpublished records of other investigators who have collected and studied the Cladocera and Copepoda of Lyon County during the past ten years (Ratzlaff 1951, Wilhm 1955, and Davies 1958). This list is obviously not complete but rather it is a basis for future studies in Lyon County and for a comprehensive check list of the entire state. It is hoped that the present list will be of value by showing which species are most likely to appear in samples taken from Lyon County and possible patterns of seasonal and habitat occur