Aging in Brachionus plicatilis: The evolution of swimming as a function of age at two different calcium concentrations

Species composition and density of cladoceran populations changed in Lakes Zürich, St. Mortiz and Baldegg as human populations increased in these watersheds. Lake Zürich sediments became annually laminated in the 1890's as a result of increased organic input as the size of the cities surrounding the lake grew. At the same time, the Bosmina species changed from a oligotrophic form (longispina) to a eutrophic form (longirostris). An increase in Daphnia spp. populations also occurred at this time in the lake's history. Bosmina longispina reappeared in the lake in 1965 as the lake's trophic status changed from eutrophic to mesotrophic due to effective sewage treatment facilities. Annual laminations appear in the Lake St. Moritz sediments about 1910. Shortly thereafter, a shift from B. longispina to B. longirostris occurred. This change in trophic status is associated with increased tourism in the area. Lake Baldegg sediments also show annual laminations beginning in 1885 and a similar shift in the Bosmina species. Other cladoceran remains were too scarce to be useful in interpreting the histories of these lakes.     

Major changes in pelagic rotifers during natural and forced recovery from acidification

Pelagic rotifers were studied in lakes with contrasting acidification histories situated in an acid-stressed region of southern Norway. Life histories and spatial distribution varied considerably between the investigated species, and influenced the recovery processes. Most headwater lakes have experienced strongly acidified environments during the last five decades, whereas lakes close to the Skagerrak coast have been stable within the same period. Rotifer diversity and abundance were reduced in the most acidic sites and increased towards the coast. Most surveyed species are known to possess sediment egg-banks, and after chemical recovery most rotifers dispersed into the plankton from these egg-banks and produced viable populations. Some species of the genera Polyarthra and Collotheca, and the species Kellicotta longispina and Keratella serrulata showed a striking ability to tolerate acidification, and were the dominant taxa in the acidmost environments. K. serrulata characterised, but did not numerically dominate, acid rotifer communities especially in the most coloured sites, and decreased following liming. The predominantly bacteriophageous genus Conochilus exploded in numbers shortly after liming, most probably because bacteria increased strongly during this transition phase. Planktivorous fish influenced indirectly rotifer abundance by consuming invertebrate predators and important rotifer competitors such as filter feeding cladocerans. Invertebrate predators, such as larvae of Chaoborus spp. and Heterocope saliens probably influenced rotifer distributional patterns in a complex top-down manner, both during chronic acidification and liming in environments with low fish predation. Important rotifer predators such as pelagic cyclopoid copepods, Bythotrephes longimanus and Leptodora kindti, were absent from the most acidic fishless lakes. Considerable populations of large-sized Daphnia longispina probably suppressed several rotifer species in sites with low fish predation, as did large populations of Bosmina longispina and Ceriodaphina quadrangula in lakes with intense fish predation.     

Effects of acidic pH and phytoplankton on survival and condition of Bosmina longirostris and Daphnia pulex

The effects of pH, algal composition and algal biomass on abundance, size, reproduction and condition of Daphnia pulex and Bosmina longirostris were tested in a field experiment using water and natural phytoplankton assemblages from a circumneutral (pH 6.43) and a moderately acidic (pH 5.75) lake in south-central Ontario. Both species were affected by pH and phytoplankton composition, with decreased egg production, lipid reserves, body size or abundance in treatments containing algae and/or water from the more acidic lake compared to treatments containing water and phytoplankton from the circumneutral lake. This result was unexpected for Bosmina, which often increases in relative and/or absolute abundance in acidified lakes. The negative effect of acidic conditions on Bosmina suggests that the population increase observed in most acidified lakes is not due to a positive response to low pH or ambient phytoplankton, but to altered biotic interactions possibly involving reduced competition.     

Aquatic Ecosystem Responses to Rapid Recovery from Extreme Acidification and Metal Contamination in Lakes Near Wawa, Ontario

In the region northeast of Wawa, Ontario (Canada), many circumneutral lakes downwind of a nearby iron-sintering plant were strongly acidified (pH 3–4) in response to the emissions of large amounts of sulfur dioxide from 1939–1998. Following closure of the plant in 1998, lakewater pH has returned to circumneutral conditions due to the high buffering capacity of the local geological substrate. Prior paleolimnological analyses of dated sediment cores have detected some biological recovery among algal communities (diatoms and chrysophytes), although they have not returned to their pre-impact assemblages. Here we take a broader ecosystem approach, and build upon the algal analyses by examining cladoceran sedimentary assemblages, and spectrally-inferred chlorophyll a and dissolved organic carbon (DOC) from the same dated sediment cores. Similar to the algal communities, recent cladoceran sedimentary assemblages from three impacted lakes remain in an altered state relative to the pre-impact period (for example, increased relative abundances of Chydorus brevilabris and reduced cladoceran density in sediments). However, trends in the spectrally-inferred chlorophyll a and DOC were mixed, with long-term decreases in the study lake closest to the plant and long-term increases within the other lakes. Collectively, the multi-proxy paleolimnological analyses of these markedly acidified lakes demonstrate the delayed biological recovery from acidification (and differences in timing) across multiple trophic levels, despite the near-elimination of acid deposition almost a decade previously, which led to a striking recovery in lakewater pH and increased food availability.     

Effects of production, sedimentation and taphonomic processes on the composition and size structure of sedimenting cladoceran remains in a large deep subalpine lake: paleo-ecological implications

Changes in the composition and size structure of cladoceran remains collected in sediment traps (ST) were compared at a monthly time-resolution to the changes in the cladoceran source communities in order to assess the effects of production, sedimentation and taphonomic processes on the composition, completeness of time series and size structure of cladoceran remains in a large deep monomictic subalpine lake. Cladoceran remains collected in the ST globally reflected seasonal changes in the composition of the source community for the dominant taxa (Daphnia sp., Eubosmina spp. and. D. brachyurum) but failed in capturing accurately the seasonal changes in the abundance of the least abundant species, B. longirostris. Using allometric relationships, the average body size of the organisms that produced the remains retrieved in the ST could be reconstructed. Although the cladoceran average body size estimated from trap remains was always smaller than that of the source communities, temporal changes in the average body size of the dominant taxa in the source community were captured by trap samples. Our results showed that, in this deep subalpine lake, cladoceran remains production, sedimentation and taphonomic processes within the water column did not alter the compositional fidelity of remains at seasonal and annual time scales for the dominant taxa. Results did not show any significant over-representation of Bosmina and subsequent under-representation of Daphnia in contrast to previous studies on small and flat lakes. Our results suggest that the frequently observed under-estimation of Daphnia in fossil assemblages could be a consequence of the mesh size used when processing sediment core samples rather than of varying magnitude of degradation processes between small or flat lakes and deep lakes. Finally, our results support the use of the size of cladoceran remains within paleo-ecological studies to assess past changes in the size structure of the source communities.     

Elevated metal concentrations inhibit biological recovery of Cladocera in previously acidified boreal lakes

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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.     

Patterns in the Distribution of Cladocerans (Crustacea: Branchiopoda) in Lakes Across a North–south Transect in Alaska, USA

The remains of cladocerans were examined from the surface sediments of 51 freshwater sites along a north–south transect spanning Alaska. We identified 27 cladoceran taxa from the sediments, consisting primarily of littoral chydorid species. Variations in cladoceran assemblages were related to measured physical and chemical variables using multivariate techniques. Redundancy analysis (RDA) indicated that lake depth, total phosphorus (TP), and altitude all had a significant influence in determining the composition of cladoceran assemblages. Cladoceran communities in tundra and forest-tundra lakes, which were relatively shallow and nutrient-poor, had relatively low abundances of pelagic Cladocera, and were primarily composed of several littoral chydorid species. Among pelagic cladoceran species, there was a distinct shift in dominance from the Bosminidae in lakes in the southern boreal forest region to Daphniidae in lakes in the northern boreal forest. Daphnia dominated lakes had significantly higher total phosphorus, specific conductivity, and calcium concentrations than lakes dominated by Eubosmina. Overall, the relative importance of physical and chemical factors in structuring cladocerans is similar to other previously studied regions, and suggests the Cladocera may be useful as ecological and paleoenvironmental indicators in this region.     

Cladocera assemblages from the surface sediments of south-central Ontario (Canada) lakes and their relationships to measured environmental variables

Fossil cladoceran remains preserved in surface sediment samples from 44 oligotrophic lakes in south-central Ontario were examined to evaluate the relationships between species assemblages and measured environmental variables. Differences in cladoceran assemblages were related to physical and chemical variables using multivariate techniques. Redundancy Analysis (RDA) identified five environmental variables as significantly influencing assemblage composition: sulphate (SO₄²⁻), calcium (Ca²⁺), pH, maximum lake depth (Z _max) and dissolved organic carbon (DOC). There was a distinct separation of lakes and taxa along the ion gradient based on SO₄, Ca and pH. Additionally, cladoceran communities in coloured, shallow lakes had relatively higher abundances of littoral chydorid species and the pelagic taxa Holopedium spp., and the Daphnia pulex complex. Deep, clear lakes had relatively higher abundances of other pelagic taxa. Predation by fish (measured as presence–absence) and Chaoborus (measured as density) were less significant than some of the physico-chemical variables in influencing cladoceran assemblage structure. However, this could be due to the limited resolution of the predation data that was available at the time of this study. The distribution of cladocerans in the surface sediment, and their relation to these important environmental variables, suggests that there is considerable potential for the use of sedimentary cladoceran remains as environmental indicators in south-central Ontario lakes. Handling editor: J. Saros     

Can extreme morphology in Bosmina reduce predation risk from Leptodora? An experimental test

Bosmina (Cladocera) populations, especially within the subgenus Eubosmina, show a variety of phenotypes that exhibit large differences in body size and shape and antennule length. In some populations, the morphological traits also vary during the season, with the most extreme forms occurring in periods with high densities of certain invertebrate predators. However, while temporal phenotypic variation in other cladocerans, as in the family Daphnidae, has been shown to be an adaptation to reduce the risk of predation by invertebrate predators, the reason for such changes in Bosmina is much less clear. We examined whether certain morphological traits in Bosmina species could act as a defence against invertebrate predators. We tested three Bosmina forms (subgenus Eubosmina), differing in morphology from each other, which are found in lakes together with the predator Leptodora kindtii (Cladocera). Bosmina (E.) longispina has a relatively low and elongated carapace with a caudal mucro, and short antennule, B. (E.) coregoni gibbera has a higher and more protruding carapace without caudal mucro, and a much longer antennule. Finally, B. (E.) coregoni retro extensa has a carapace like that of B. longispina but with no caudal mucro and a much longer antennule. In one experiment, B. longispina and B. gibbera were exposed for 12 h to Leptodora in Petri dishes. In a second experiment, we observed directly the escape efficiency of B. longispina, B. gibbera and B. retro extensa, and the handling time of Leptodora. The two Bosmina forms with more extreme morphological features had a lower death rate and higher escape efficiency than B. longispina. Prey that escaped did so, in most cases, within 5 min. Predator handling time was correlated to predator body length and antennule length of the prey. The results suggests that Bosmina species with extreme morphological traits may be less vulnerable to invertebrate predators. Received: 8 June 1998 / Accepted: 5 October 1998     

Abrupt Changes in Bosmina (Cladocera,Crustacea) Assemblages During the History of the Ostrowite Lake (Northern Poland)

During the 10000-year history of the Ostrowite Lake, there have been several episodes of change in dominance amongst species of the genus Bosmina. The dominants were alternately B.longirostris and Eubosmina spp. Amongst the subgenus Eubosmina, two species prevailed in different periods:Bosmina coregoni and Bosmina reflexa. The first species, Bosmina coregoni, is characterized by long antennae and short carapace mucrones, while the second one, Bosmina reflexa, by short antennae and very long mucrones. Bosmina reflexa was dominant at the beginning of the lake's history (Preboreal, 10000--9000 BP) and during the early Subboreal Period (5000–3500 BP). Only a small number of remains of Bosmina longispina(Eubosmina spp.) were present along the entire profile. Such strong changes in the domination of Bosmina species were observed for the first time in the sediments of Polish lakes. A similar transition from one species to another has been described in a few German lakes and was linked to climate changes. However, the changes in the Ostrowite Lake do not correlate with climate changes, but most probably, with changes in the lake's trophic level. This is suggested by the simultaneous increase of Bosmina reflexa and a good indicator of eutrophy, Bosmina longirostris.     

Sub-fossils of cladocerans in the surface sediment of 135 lakes as proxies for community structure of zooplankton,fish abundance and lake temperature

To elucidate the possibilities of using zooplankton remains in the surface sediment to describe present-days community structure and population dynamics of zooplankton, fish abundance and temperature, we compared contemporary data sampled in the pelagial during summer with the sediment record from the upper 1 cm of the sediment in 135 lakes covering a latitude gradient from Greenland in the north to New Zealand in the south. The abundance of three genera Bosmina, Daphnia and Ceriodaphnia of the total pool of ephippia was significantly related to the total abundance of the same taxa in the pelagic zone. However, in most lakes the abundance of Ceriodaphnia was higher in the sediment than in the water, which may be attributed to the overall preference by this genus for the littoral habitat. Using contemporary data from 27 Danish lakes sampled fortnightly during summer for 10 years, we found substantial inter-annual variations in the abundance of Daphnia spp., Ceriodaphnia spp., B. longirostris and B. coregoni. Yet, the sediment record mimicked the medium level well for most of the lakes, which suggests that the sediment record provides an integrated picture of the pelagic cladoceran community, which otherwise can be obtained only by long-term frequent contemporary sampling for several years. The contribution of Daphnia to the sum of Daphnia and Bosmina ephippia was negatively correlated with the abundance of fish expressed as catch per night in multi-mesh sized gill nets (CPUE). Yet, region-specific differences occurred, which partly could be eliminated by including nutrient state expressed as total phosphorus (TP) in a multiple regression. The average ratio of ephippia to the sum of ephippia and carapaces of Bosmina varied 40-fold between the sampling regions and was significantly negatively related to summer mean air temperature, and for Danish lakes also, albeit weakly, to fish CPUE but not to chlorophyll a. Apparently, temperature is the most important factor determining the ratio of parthenogenetic to ephippia producing specimens of Bosmina. We conclude that the sediment record of cladocerans is a useful indicator of community structure of pelagic cladocerans and the abundance of fish and temperature.     

Experimental analysis of the predation impact of the larvae of pond smelt (<Emphasis Type="Italic">Hypomesus transpacificus nipponensis</Emphasis>) on zooplankton populations established in mesocosms

The predation impact of the larvae of pond smelt Hypomesus transpacificus nipponensis on a zooplankton community was studied using mesocosms. The fish significantly depressed the abundances of copepod nauplii and rotifers, especially Hexarthra mira. The vulnerabilities of these prey might be determined by their swimming behavior and population density, suggesting that larval fish selectively prey on zooplankton that have a high encounter rate with the predator. The larvae did not have a negative effect on the densities of cladocerans, but fish predation altered the cladoceran community structure from the dominance of B. longirostris to that of B. fatalis. This result suggests that larval fish predation is an important factor that shifts the species composition of Bosmina in some lakes, the shift occurring in the season when fish larvae are abundant. Our results have shown that predation by the larval fish would control not only the abundance, but also the community structure of the small-sized zooplankton prey.     

Acidity versus habitat structure as regulators of littoral microcrustacean assemblages

1. Emergence traps were set overnight on the sediment surface to sample the littoral microcrustaceans of 22 Canadian Shield lakes that ranged in pH from 4.56 to 6.92. Traps were randomly allocated in quintuplicate in both wave‐washed sandy habitats where pipewort (Eriocaulon septangulare) was the dominant macrophyte (termed pipewort habitats), and more protected habitats dominated by floating‐leaved macrophytes (termed floating‐leaved habitats). 2. In total, 50 cladoceran and 22 copepod species were found, with 16–45 species in each lake. Lakes that had never acidified exhibited a more diverse fauna than lakes that had acidified. 3. There were only minor differences between the numbers of species found in floating‐leaved versus pipewort habitats except for one lake. Non‐chydorid cladoceran, chydorids and copepods constituted 45%, 26% and 29% of the total number of individuals, respectively. 4. Based on presence/absence, dominance scores and frequency of occurrences of species, the microcrustacean faunal composition was similar in the two habitats. A detrended correspondence analysis confirmed that there was no separation between the two main types of habitat, and that pH was the parameter most strongly correlated with the dominant microcrustacean compositional gradient among lakes.     

The late Pleistocene/Holocene and recent Bosmina (Eubosmina) fauna (Crustacea: Cladocera) of the pre-alpine Starnberger See (FRG)

An analysis of the remains of Bosmina (Eubosmina) in a sedimentcore from the pre-alpine, mesotrophic Starnberger See showedthat the lake was inhabited by B. longispina since the OldestDryas. In the Subatlantic- -1900 years ago — the kesslerimorph of B. coregoni invaded the lake and both taxa have sinceco-existed. Although there was considerable morphological variation,B. longispina clearly differed from Circumbaltic populationsthrough most of the late Pleistocene and Holocene periods. Inthe recent Bosmina fauna of the lake two morphologically wellseparated taxa (B. longispina ruehei and a morph of B. coregoni)occur which differ clearly from the Bosmina remains found inthe core up to the uppermost sample from 7 cm sediment depth.B. coregoni f. kessleri appeared in the lake in a period whenit was supposedly still oligotrophic. The Bosmina successionobserved in the Starnberger See resembles the pattern foundin deep north German lakes.     

The influence of calcium decline and climate change on the cladocerans within low calcium, circumneutral lakes of the Experimental Lakes Area

Calcium (Ca) concentrations of many softwater lakes on the Canadian Shield have been in decline for decades as a response primarily to regional acid deposition and repeated cycles of forest harvesting. These Ca declines are of ecological interest, as many lakes have fallen to Ca levels detrimental to the fitness of ecologically important Ca-rich cladoceran taxa such as Daphnia pulex. However, distinguishing the impacts of reduced Ca from acidification (i.e., decreasing pH) on Ca-demanding fauna has proven difficult due to strong correlations between pH and Ca in softwater lakes. Here, we examine cladoceran sedimentary assemblages from low Ca lakes (mean present-day Ca < 2.0 mg l^?1) in the Experimental Lakes Area (ELA) of Ontario, Canada, where Ca concentrations have declined since the 1980s, despite being closed to forestry and remote from (i.e., not downwind of) major sources of acid deposition. Differences between present-day and pre-industrial cladoceran assemblages were greatest among planktonic taxa, including Bosmina spp. and Holopedium glacialis. However, daphniid remains were present in only three of the ten study lakes with minimal directional trends. Overall, in these ELA lakes, daphniid abundance was low historically, and impacts possibly attributable to Ca declines have been obscured by the effects of regional climate warming.     

Chlorophyll budgets: response to food web manipulation

Budgets for chlorophyll a and selected degradation products were constructed during summer stratification in 1984 and 1985 in two lakes. In Paul Lake, the reference ecosystem, pigment sedimentation showed no significant interannual differences. In Tuesday Lake, fish manipulations in May 1985 changed the zooplankton from an assemblage of Bosmina and small cyclopoids to one of large cladoceran grazers. Sedimentation of pigments, especially the grazing indicator pheophorbide a, increased significantly as the grazer assemblage changed. Mean grazer size was positively related to pheophorbide deposition rate in both lakes. Results of this whole-lake experiment indicate that major changes in lake food webs alter pigment deposition rates.     

Zooplankton of lakes in the spurs of the Putorana Plateau and adjacent territories (North of Krasnoyarsk Krai)

Species composition and parameters of biomass of net plankton were analyzed for four large and 35 small lakes from 10 areas located between 69.5° and 67.5°N and 87° and 92°E that were examined in July–August, 2001 and 2003–2004. In the composition of the first (dominant) and/or second (subdominant) species in the ranged row of the average biomass, the lakes were copepod in 78.8% of cases, in 67.3%, calanoid. The share of biomass of cladocerans in the total biomass of zooplankton exceeded 50% only in 31% of cases. By the frequency of occurrence as dominant or subdominant by biomass the first place is occupied by copepodites calanoid (34.6% of cases), the second, by sexually mature Heterocope appendiculata (26.9%), the third, by copepodites cyclopoid (17.3%), the fourth, by Polyphemus pediculus (15.4%), the fifth, by Acanthodiaptomus denticornis (13.5%), the sixth, by Bosmina cf. longispina (11.5%), the seventh, by Heterocope borealis (9.6%), the eighth, by Daphnia cf. longispina (7.7% of cases). For the first time in the region 14 species of crustacean zooplankton are given. The known range of some species and subspecies (for example, Chydorus biovatus, Camptocercus fennicus, Ophyoxus gracilis kolymensis, Arctodiaptomus acutilobatus, Acanthrodiaptomus tibetanus) is widened owing to the findings in the studied region. The groups of the areas are more similar in terms of zooplankton north to south than east to west; the number of the cladoceran species and the number of cladoceran lakes grew north to south and east to west, which corresponded to the general change of climate towards more mild north to south for similar altitudes and east to west for different altitudes from mountain areas to the low lands. The comparison of the species lists from different northern regions showed that the species diversity (total number of species) of cladocerans and copepods does not change significantly west to east. Distribution of species and changes in the zooplankton structure are discussed from the point of view of possible influence of the global warming.     

The late Holocene appearance of European Bosmina (Eubosmina) thersites (Crustacea, Cladocera) in lakes surrounding the Baltic Sea

This study shows the appearance of Bosmina (Eubosmina) thersites during the last millennium in two lakes in Northern Europe: Lake Charzykowskie (Poland) and Lake Lohja (Estonia). Cladocera remains collected from both lakes showed similar Bosmina species composition and changes during the late Holocene. Older sediment layers showed a prevalence of smaller Eubosmina species (B. (E.) longispina), indicating oligotrophic conditions of the lakes, while younger layers were dominated by larger species (B. (E.) coregoni and B. (E.) thersites), typically found in lakes with higher trophy. The presence of B. (E.) thersites has rarely been reported in paleolimnological research, and this is the first observance of its high abundance in lake sediments. More research is needed, however, to better understand the appearance, speciation driver, continental range, and ecological preferences of B. (E.) thersites.     

Increasing dominance of small zooplankton with toxic cyanobacteria

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