Alona Rectangula Research Articles

Effect of Aeolosoma sp. (Aphanoneura: Aeolosomatidae) on the Population Dynamics of Selected Cladoceran Species

Although oligochaete worms naturally coexist with cladocerans in many shallow freshwater ponds and lakes, their influence on the latter is not well established. In this work we studied the effect of Aeolosoma sp. on the population growth of Alona rectangula, Ceriodaphnia dubia, Daphnia pulex, Macrothrix triserialis and Moina macrocopa. Population growth studies were conducted at one algal food density (1 × 106cells ml−1 of Chlorella vulgaris). The experimental design was similar for all five cladoceran species, where we used 100 ml capacity transparent jars containing 50 ml of EPA medium with the desired algal density and three replicates for each treatment. The test medium was changed daily and fresh algal food was added. The initial density of each of the cladoceran species in the population growth studies was 0.4 ind ml−1 while that of the worms 1.0 ind ml−1. Following inoculation, we estimated daily the number of cladocerans and the worms for duration of 21 days. Regardless of the presence of worms, Moina macrocopa and Macrothrix triserialis showed rapid population growth while A. rectangula took more than 2 weeks to reach peak abundances. With the exception of M. triserialis, all the other our cladoceran species declined in the presence of Aeolosoma sp. The lowest peak population density (about 1 ind ml−1) was observed for M. triserialisin controls. The remaining species had peak densities of about 3–5 ind ml−1. The rates of population increase per day varied from 0.03 to 0.19 depending on the cladoceran taxa and the treatment. In general we found that pelagic taxa were more adversely affected by the presence of the worms than were the littoral cladocerans.

Do Littoral Macrophytes Influence Crustacean Zooplankton Distribution?

In a meso-eutrophic reservoir, cladoceran and copepod assemblages were characterised in two sampling sites: One located in the pelagic zone (site 1) and the other in the shallow littoral zone (site 2), the latter colonised by emergent macrophytes. Samples were collected biweekly from June to July 2001 and from May to July 2002 at the two sites. At site 1, crustacean zooplankton samples were obtained by vertical hauls using a Wisconsin type net of 64 mm mesh size. At site 2 several random samples were obtained using a van Dorn bottle. Those samples were pooled together and the total sample was sieved through a 64 mm mesh size. Macrophyte relative abundance for each species was visually estimated. Macrophyte community was composed of Glyceria declinata, Eleocharis palustris and Carex sp. A Mann-Whitney U-test was carried out to test for statistically significant differences between sites, for environmental parameters and crustacean zooplankton species densities. Alona rectangula, Alona costata, Alona quadrangularis and Chydorus sphaericus were only found in littoral samples. Daphnia longispina, Daphnia pulex, Ceriodaphnia pulchella, Bosmina longirostris, Diaphanosoma brachyurum, Copidodiaptomus numidicus, and Acanthocyclops robustus were found at both sites. However, Daphnia and Bosmina densities did not differ significantly between the pelagic and littoral sites. Ceriodaphnia, Diaphanosoma, and C. numidicus densities were significantly higher in the pelagic site, whereas A. robustus densities showed the opposite pattern. Key-words: Zooplankton, Cladocera, Copepoda, reservoir, macrophytes, pelagic zone, littoral zone

Long-term changes in benthic Cladocera populations in Lake Myvatn, Iceland

Benthic Cladocera were monitored at five sites in Lake Myvatn, Iceland, over a decade (1990–1999), as part of a programme documenting the population fluctuations of animals at different trophic levels in the lake. The species composition remained relatively stable over the first seven years, but in 1997 the population of Eurycercus lamellatus was greatly reduced at all sites. The following year saw a mass occurrence of Alona rectangula and Alonella nana that were previously abundant only locally and rare at most sites. Alona affinis, A. quadrangularis, Acroperus harpae and Chydorus sphaericus were not affected. In 1999 the Cladocera assemblages returned to the pre-1997 situation. The shift was from large-bodied epibenthic and planktonic species (Eurycercus, Daphnia) to small infaunal (Alona rectangula) and ubiquitous (Alonella nana) species. Medium sized (Alona, Acroperus) and some small cladocerans (Chydorus) were not affected. The course of events was reminiscent of a trophic cascade caused by a change in size-selective predation pressure. If so, the impact of a predatory fish population (three-spined stickleback, Gasterosteus aculeatus) depended on whether cyclic chironomid populations were in a high or a low phase. The change in the Cladocera coincided with profound changes in the sediment characteristics associated with low chironomid abundance. We suggest that the relative competitive ability of the Cladocera species is reversed when the sediment has become homogeneous and nutrient-poor after overexploitation by the dominant, tube building and detritivorous chironomid Tanytarsus gracilentus.

Food Type Effects on the Population Growth Patterns of Littoral Rotifers and Cladocerans

AbstractLittoral rotifers and cladocerans feed on bacteria, phytoplankton, and detritus. In comparison to planktonic organisms their species diversity is high, yet little is known about their biology. In this study we present data on the functional response of the cladocerans Macrothrix triserialis and Alona rectangula, and the rotifer Brachionus macracanthus to different levels of the alga Chlorella vulgaris. Based on the incipient limiting level, we chose the food concentration and tested the population growth on four types of diets for three cladoceran species — Macrothrix triserialis, Alona rectangula, and Chydorus sphaericus — and three rotifer species — Brachionus macracanthus, Lecane quadridentata, and Platyias quadricornis. We studied growth rates of each of these species on diets of live Chlorella vulgaris, heat‐killed Chlorella vulgaris, baker's yeast (Saccharomyces cerevisiae), and field collected detritus. The incipient limiting level was around 0.9 · 106 cells mL−1 of Chlorella for the tested zooplankton species. The population growth patterns showed that, in general, the cladocerans took 25…50 d to reach their peak population densities, which ranged from 10…75 ind. mL−11. Among the rotifers L. quadridentata and B. macracanthus had equally high growth rates on live and heat‐killed forms of C. vulgaris while P. quadricornis grew best on detritus. The growth rates ranged from 0.03…0.21 d−1. The similarities and differences between littoral and planktonic organisms in relation to food type and availability have been discussed.

The distribution of chydorids (Branchiopoda, Anomopoda) in European shallow lakes and its application to ecological quality monitoring

This study describes the chydorid (Branchiopoda, Anomopoda) assemblages from 66 European shallow lakes, and presents data relating the assemblages to lake type and ecological quality. Forty species, out of a total recorded European fauna of 60 species, were found in the study sites. No significant differences were found between chydorid assemblages associated with rock and plant substrata. Patterns of distribution were best explained primarily by latitude and pH. Chlorophyll-a, total phosphorus, water temperature and Secchi depth were also correlated with assemblage descriptors. Alonopsis elongata, Alona rectangula, Alonella excisa and Pleuroxus uncinatus were shown to have higher prevalence in certain lake types. The dominance of Chydorus sphaericus in a third of the study sites was linked to eutrophication and high levels of chlorophyll-a. The relationship between chydorids and lake ecological quality was more apparent at species rather than community level. This study identifies important typological factors affecting chydorid distribution, and confirms that patterns of chydorid distribution previously reported from regional studies hold true across Europe.

Population growth of some genera of cladocerans (Cladocera) in relation to algal food (Chlorella vulgaris) levels

We studied the patterns of population growth of 7 cladoceran species (Alona rectangula, Ceriodaphnia dubia, Daphnia laevis, Diaphanosoma brachyurum, Moina macrocopa, Scapholeberis kingi and Simocephalus vetulus) using 6 algal densities, viz. 0.05×106, 0.1×106, 0.2×106, 0.4×106, 0.8×106 and 1.6×106 cells ml−1, of Chlorella vulgaris for 18 – 30 days. In terms of carbon content these algal concentrations corresponded to 0.29, 0.58, 1.16, 2.33, 4.65 and 9.31 μg ml−1, respectively. Cladocerans in the tested range of algal levels responded similarly, in that increasing the food concentrations resulted in higher numerical abundance and population growth rates (r). The peak population densities were (mean±standard error) 71±5; 17.1±0.4, 3.6±0.3, 12.7±1.1, 18.2±2.7, 15.8±1.0 and 10.9±0.02 ind. ml−1, respectively for A. rectangula, C. dubia, D. laevis, D. brachyurum, M. macrocopa, S. kingi and S. vetulus. In general, the lowest r values were obtained for D. laevis (0.01±0.001) at 0.05×106 cells ml−1 food level while the highest was 0.283±0.004 for A. rectangula at 1.6×106 cells ml−1 of Chlorella. When the data of peak population density for each cladoceran species were plotted against the body length, we found an inverse relation, broadly curvilinear in shape. From regression equations between the food level and rate of population increase, we calculated the theoretical food quantity (the threshold level) required to maintain a zero population growth (r = 0) for each cladoceran species, which varied from 0.107 to 0.289 μg ml−1 d−1 depending on the body size. When we plotted the cladoceran body size against the corresponding threshold food levels, we obtained a normal distribution curve. From this it became evident that for up to 1300 μm body size, the threshold food level increased with increasing body size; however, beyond this, the threshold level decreased supporting earlier observations on rotifers and large cladocerans.

Subfossil littoral Cladocera as indicators of brackish‐water Littorina transgression of the Baltic Basin in a small lake in Finland

The study aimed to investigat e the value of freshwater littoral Cladocera (chydorids, Ophryoxu s gracili s and Sida crystallina) in stratigraphical studies of shore displacement of the Baltic Sea. Diatoms and Cladocera were analysed from a sediment core from Lake Ruokolampi (S Finland, 60°34'N, 27°26'E), where a brackish‐water Baltic transgression (Littorina Sea) is clearly expressed by changes in lithology. The diatom flora indicates a development of the waterbody from an Ancylus Lake bay to a small lake that was subject to a brackish Littorina transgressio n followed by another small‐lake stage. There was a rich chydorid fauna in the Ancylus Lake bay and the following small lake. Littoral Cladoceran diversity fell sharply at the onset of the brackish transgression; however, three species (Alona rectangula, Alona affinis and Chydorus sphaericus s.l.) appear to have been tolerant of the saline conditions. Concentrations of all species rose rapidly after the transgression. Littoral Cladocera appear to react to the inflow of brackish water as sensitively as the diatoms and may provide a valuable additional method for pinpointing Baltic Sea transgression and isolation events, especially in cases where the diatom and biostratigraphical evidence is not as clear as in the Ruokolampi sequence.

Comparative Life Table Demography and Population Growth of Alona rectangula and Macrothrix triserialis (Cladocera: Crustacea) in Relation to Algal (Chlorella vulgaris) Food Density

ABSTRACT We conducted survivorship and population growth studies with two littoral-benthic cladocerans, Alona rectangula and Macrothrix triserialis, littoral-benthic cladocerans, under low and high food levels (0.5×106 and 2.0×106 Chlorella vulgaris cells ml−1). The net reproductive rate ranged from 13 to 15 offspring/female in the case of A. rectangula and between 19 and 27 for M. triserialis. The generation time was also lower (10 d) for A. rectangula but higher (16–18 d) for M. triserialis. Thus, the growth rates of M. triserialis were around 0.25 d−1 while those of A. rectangula around 0.32. The rates of population increase from the population growth experiments were lower than those from the life table demography studies.

Studies on functional response and prey selection using zooplankton in the anostracan Chirocephalus diaphanus Prevost, 1803

Freshwater cladocerans and rotifers were used as prey to study functional response and prey selection by adult females of Chirocephalus diaphanus under laboratory conditions. For functional response studies, we offered three rotifer species (Brachionus calyciflorus, B. patulus and Euchlanis dilatata) and three cladoceran species (Alona rectangula, Ceriodaphnia dubia and Moina macrocopa) at various densities ranging from 0.5 to 16 ind. ml−1. We found increased zooplankton consumption with increasing prey density but beyond 4 ind ml−1 cladocerans and 8 ind. ml−1 rotifers, the number of animals eaten plateaued. In general, C. diaphanus consumed fewer large prey (cladocerans) and many more smaller zooplankton (rotifers). For prey selection experiments, we used B. calyciflrous, B. patulus, C. dubia and M. macrocopa, offered at the ratio of two rotifers: one cladoceran and at three prey densities (total zooplankton numbers: 3, 6 and 12 ind. ml−1). Prey selectivity patterns followed the functional response trends. In general, regardless of prey types, with an increase in the available zooplankton, there was an increase in the number of prey consumed. At any given prey density, C. diaphanus consumed higher numbers of rotifers than cladocerans. Among the prey offered, B. patulus and M. macrocopa were positively selected. Results are discussed in light of possible control of zooplankton by anostracans in temporary ponds.

Cladoceran assemblages in a mineralization gradient

Cladoceran assemblages were studied in littoral samples from 44 water bodies in Central Spain, showing great differences in salinity and permanence of water. Principal component analyses (PCA) were performed with data on cladoceran relative abundances to identify the main groups of species. Five main groups of species were found, defining the following types of environments: (I) Small but deep hard water lakes (II) permanent but shallow hard water lakes fed by surface springs, rich in macrophytes (III) ephemeral and shallow soft waters lakes (IV) subsaline and hyposaline lakes in their lower range, specially the permanent ones and (V) saline lakes (salinities>6 mg l−1) subject to short or long periods of dryness. The main species constituting these groups were: Group (I): Acroperus neglectus, Alona guttata, Pleuroxus truncatus, Daphnia longispina; group II: Phrixura leei, Latonura rectirostris, Eurycercus lamellatus; Alonella excisa, Daphnia pulicaria; group III: Ephemeroporus phintonicus, Macrothrix rosea, Moina micrura; group IV: Alona rectangula, Ceriodaphnia reticulata, Tetrocephala ambigua, Diaphanosoma mongolianum; group V: Alona salina, Pleuroxus letourneuxi, Dunhevedia crassa, Moina brachiata, Daphnia magna and Daphnia mediterranea. Sample scores from PCA extracted from the correlation matrix of cladoceran proportions were correlated with limnological measurements. Significant correlations with salinity, alkalinity anions and cations indicate that salinity is an important factor in the distribution of the species. However, species assemblages also reflect other factors, such as temporality and littoral development.

Alona weinecki Studer on the subantarctic islands, not Alona rectangula Sars (Chydoridae, Cladocera)1

Since Harding in 1967 named the Alona on Signy Island (South Orkneys) Alona rectangula, this binomen has persisted there and has been extended to other island groups in the Scotia Arc. Elsewhere among the subantarctic islands the binomen Alona weinecki has been used, based on a description in 1878 and a redescription in 1914. A detailed redescription of A. rectangula from Norway and Denmark permitted comparison with available populations of A. weinecki from Signy and South Georgia and of the synonymous taxa Alona bukobensis var. subantarctica and Alona subantarctica. The two taxa, although related, are completely different. Alona rectangula sens. str. does not occur on the subantarctic islands at all.Whether the A. weinecki populations on these islands are the same species is presently unknown. Specimens on Kerguelen Island are reported to be larger than those on the Scotia Arc islands, and among the latter populations there are differences in structure of at least the labrum. The islands in the Scotia Arc, except the Falklands, were completely ice covered during the last glacial age, with documented advances and retreats of the glaciers during the Holocene until 2000 b.p. Conditions on at least some other subantarctic islands were probably comparable. If the Cladocera were eliminated by glacier advances, the islands must have been recolonized during the Holocene from a refugic population, possibly in the Falklands. Strong westerly winds and migration of sea birds might have spread the taxon. If the populations are different, however, then the taxa must have survived on their respective islands during the glacial ages. Large populations containing ephippial females and the three instars of males are needed to resolve this uncertainty.Lectotypes of A. rectangula Sars, A. bukobensis var. subantarctica Ekman, and A. subantarctica Ekman have been selected and are on deposit in the Zoological Museums in Oslo and Stockholm.

Anostraca, Conchostraca, Cladocera and Copepoda from Tunisia

In samples from 62 localities in Tunisia and La Calla area in N.E. Algeria, 56 species of Entomostraca were found. More than half of these are widespread and give little insight into the origin of the regional fauna. A few are endemic to the area and three groups are of relictual nature. The first one consists of northern species, some of which are known to have reached the central Sahara. It is argued that their populations have an estimated age of about 5–6000 yrs. At first sight, the second and more numerous group of species, the Ethiopian relicts, should be older. However, until historical times pathways ‘around’ the Sahara may have functioned. One was along the Atlantic coast; a second and older one was via the Nile. The second possibility is almost a certainty, since a third group of relicts, the Oriental one, has migrated into the central Sahara as far as (and therefore probably together with) the northern relicts. This group must have come via the Nile Delta and the Libyan desert. If that pathway has also been used by Ethiopian species, all three groups of relicts are of the same age. In our Tunisian collection, only one Oriental element is represented. From a taxonomical point of view, morphological differences between the Chydorids Alona rectangula Sars and Alona elegans Kurz are sorted out and illustrated. Alona rectangula is best regarded as a superspecies. Hybridisation with A. elegans appears possible.

Danish Chydorid Cladocera: Modern Ecology and Core Studies

Surficial sediments from 77 Danish lakes were processed for chydorid remains for the purpose of establishing relationships of species occurrence to lake type. A total of 35 species of chydorids was recovered; 3 species were new for Denmark, while 3 others previously reported from Danish lakes were not found. The lakes sampled were subjectively grouped according to physical—chemical measurements into 1 of 3 groups–clear—water lakes (1), ponds and bogs (2) and polluted, clear—water lakes (3). Correlations between chydorids and chemical—physical properties of lakes, plus evidence from relative abundances and frequencies of each species found in each lake type, suggests that most species prefer those waters best termed oligotrophic and dystrophic. The exceptions of Chydorus sphaericus and Alona rectangula which, when found in high percentages, typify eutrophic or polluted sites. These data correlated well with species diversity values–high values were found in clear—water lakes (1) and ponds and bogs (2), while low diversities were typical of polluted sites (3). These data suggested that species diversity is a function of available habitat (rooted aquatics), and hence to a large extent the distribution of most chydorid species within a region is determined by habitat diversity (structure). Grane Langso (an oligotrophic, Jutlandic lake) and Esrom S° (an eutrophic, Zealandic lake) were selected for paleo—studies because of their differences, which resulted in contrasting lake development. Postglacial gyttja sediment in Grane Langso extended to 431 cm below the mud—water surface interface. Pollen zonation, and a radiocarbon date of ±9500 BP placed the lowest organic deposits into Pre—Boreal time. Two chydorid species were important in Grane Langso Late—glacial sands underlying the gyttja (Alona affinis and Chydorus sphaericus). Chydorid faunas developed through the Pre—Boreal and early Boreal; by late Boreal chydorid populations were most diverse, and presumably stable. A decrease in species diversity during Atlantic time was due to unstable conditions within the lake, evidenced by deposition of sand; Chydorus piger was abundant during this period. Sub—Boreal organic deposits overlay the Atlantic sands. High percentages of Pleuroxus during mid—Sub—Boreal were attributed to man's activity, and a lower water level. The most recent change in chydorid assemblages occurred within the past 100 yrs; this change was increased percentages of Alonella nana–a species normally associated with low alkalinities in Denmark. Postglacial calcareous gyttja deposits in Esrom So extended to 380 cm below the mud water interface. Calcareous clay extended from 381—840 cm, and glacial till occurred below 840 cm. Pollen preservation was poor in Esrom, but the lowermost gyttja was probably Pre—Boreal (Zone IV). No pollen counts were attributable to Zone VI. Few chydorid remains were found in Late—glacial clays, and extensive development of populations began in Pre—Boreal time (370 cm). Chydorid assemblages characteristic of discriminant Group 1 were present throughout most of the postglacial deposits; benthic species were prevalent during most of the lake's history. Littoral forms did increase in Sub—Boreal time, but by Sub—Atlantic chydorid assemblages were again dominated by benthic groups. In Esrom, postglacial chydorid fluctuations were dampened by its morphological and chemical characteristics, while Grane Langso fossil assemblages were sensitive to minor variations in the lake's environs. Pioneer chydorid species in northern Europe are Chydorus sphaericus, Alona affinis, A. quadrangularis, Acroperus harpae, and Alonella nana.