Growth of dominant zooplankton species feeding on plankton microflora in Lake Shira

Batch cultures and continuous flow cultures were used to study the growth rates of zooplankton species from Shira lake, the rotifer Brachionus plicatilis Muller and calanoid copepod Arctodiaptomus salinus Daday, which were fed on phytoplankton and bacterioplankton from the lake. Analyses of the birth and survival rates were used to demonstrate that the lake phytoplankton, consisting mostly of cyanobacteria and diatomaceous algae, is inadequotes for optimal realisation of the reproductive potential of B. plicatilis when compared with the bacterial diet. The study revealed that the kinetic growth characteristics of the two zooplankters were similar: B. plicatilis r _max, 0.120 d^–1; S ₀, 0.253; and K _s, 0.114 mg dry mass l^–1; and for A. salinus r _max, 0.129 d^–1; S ₀, 0.240; and K _s, 0.171 mg dry mass l^–1. Fluctuations in natural food concentration reduced the growth rate of both species. Even though the threshold concentration of food for B. plicatilis and A. salinus were quite similar, the copepods were less sensitive to food limitation.     

Mating flight, metrosis, and semi-claustrality in the seed-harvester ant Pogonomyrmex salinus (Hymenoptera, Formicidae)

Here we examine dispersal, metrosis, and claustrality in the seed-harvester ant Pogonomyrmex salinus at an unusually large mating aggregation. We found that mode of queen dispersal from the mating aggregation is not a function of queen mass and that wing damage among queens was relatively rare. P. salinus is haplometrotic in the field and foundress queens placed together in forced associations eventually fight to the death. While queens of Pogonomyrmex salinus can survive claustrally, producing a single minim from their body reserves in the laboratory, fed queens produce up to four significantly larger minims along with concurrent larvae and pupae during the same period. Since queens forage in the field, we interpret claustrality as a secondary reserve strategy when foraging fails, and suggest that foraging is obligate for P. salinus queens in an overdispersed and temperate environment. Thus, nest founding strategies employed by P. salinus may be environmentally determined and represent a continuum between fully claustral and obligate foraging. We discuss our results with reference to theories of pleometrosis and claustral colony founding. Received 12 November 2004; revised 12 April 2004; accepted 29 July 2005.     

Influence of sodium orthovanadate on the production of astaxanthin from green algae Haematococcus lacustris

Astaxanthin production is commonly induced under stress conditions such as nutrient deficiency (N or P), high light stress, and variations of temperature, high NaCl concentrations, and other factors. The objective of the present study is the analysis of the effect of oxidative stress by sodium orthovanadate (SOV), a nonspecific inhibitor of protein tyrosine phosphatases, on the cells growth and astaxanthin production of H. lacustris. In the presence of SOV (lower than 5.0 mM), maximum growth of H. lacustris obtained was 2.4 × 10⁵ cells/mL in MBBM medium at 24°C under continuous illumination (40 μE/m²/s) of white fluorescent light, with continuous aeration of CO₂ (0.2 vvm). Total carotenoids accumulated per cell biomass unit treated with 2.5 mM SOV has approximately shown 2.5 folds higher than the control after short period of SOV induction time as 2 days, despite that cells were grown under normal light. Meanwhile, maximal astaxanthin production from H. lacustris was 10.7 mg/g biomass in MBBM with 5 days of continuous illumination at 40 μE/m²/s, which has been established as optimal light intensity for the control culture of H. lacustris. Treating algae H. lacustris with sodium orthovanadate showed promoting the accumulation of astaxanthin by advancing either the inhibition of dephosphorylation or synthesis of ATP. Its potential role of PTPases in microalgae H. lacustris is discussed. The first two authors are equally contributed to this work.     

Seasonal variability in the grazing potential of the invasive amphipod Gammarus tigrinus and the native amphipod Gammarus salinus (Amphipoda: Crustacea) in the northern Baltic Sea

Mesograzers are known to reduce the biomass of their host plant and modify the structure of the whole macrophyte community in many ecosystems. Thus, the introduction of an efficient mesograzer may destabilize macrophyte community and also affect the native grazers. We estimated how large proportion of macrophyte production are consumed by the alien gammarid G. tigrinus and the native gammarid G. salinus in the species poor ecosystem of the northern Baltic Sea. We analysed whether G. tigrinus consumes different diet as the native G. salinus and whether the effect of G. tigrinus on the survival of the native G. salinus is macrophyte species specific. Grazing experiments showed that there was a clear difference in the grazing rates of gammarids among the studied macrophyte species in summer and autumn but not in spring. The grazing rates were significantly higher in the prevailing macrophyte Pilayella littoralis as compared to other macrophytes. The grazing was inversely related to the diurnal net photosynthetic values of macrophytes. The gammarid amphipods potentially removed only a minor part of plant primary production except for summer and autumn when grazing of a few perennial species exceeded macrophyte production. Macrophyte species and presence of G. salinus had no effect on the survival of G. tigrinus. The presence of G. tigrinus, however, reduced the survival of the native gammarids within P. littoralis in summer. To conclude it is likely that both native and alien gammarid amphipods do not exert significant pressure on the macroalgal communities in the northern Baltic Sea. Competitive interactions between G. tigrinus and G. salinus within the prevailing macrophyte P. littoralis is the likely explanation of the decline of the native gammarid amphipods after the establishment of G. tigrinus in the northern Baltic Sea.     

Feeding spectra of <Emphasis Type="Italic">Arctodiaptomus salinus</Emphasis> (Calanoida,Copepoda) using fatty acid trophic markers in seston food in two salt lakes in South Siberia (Khakasia,Russia)

During two vegetation seasons (2004–2005), we compared feeding spectra of Arctodiaptomus salinus (Calanoida, Copepoda) populations inhabiting two neighboring salt lakes, Shira and Shunet, Khakasia, Russia, using fatty acid (FA) trophic markers. Sestonic FA composition in two lakes moderately differed, whereas levels of diatom FA markers were higher in Lake Shunet and of Cyanobacteria and green algae markers in Lake Shira. In general, markers in storage lipids—triacylglycerols (TAG) of A. salinus—reflected the differences in sestonic composition of the two lakes. Nevertheless, TAG fraction was also enriched by FA trophic markers of the minor components of seston, which were selectively ingested by the animals. In Lake Shira, A. salinus had significantly higher concentrations of bacterial FA markers in TAG. In Lake Shunet, TAG of A. salinus contained significantly higher relative amounts of 18:4ω3, 18:5ω3 and C22 polyunsaturated fatty acids (PUFA), which indicated marked contribution of cryptophytes or (and) flagellates into the diet. Laboratory experiments showed feeding on Cryptomonas and sulfur purple bacteria in Lake Shunet and ciliates and colonial picoplankton in both lakes, and generally confirmed the differences in FA trophic markers in A. salinus between the lakes. The two populations of A. salinus markedly differed in levels of essential long-chain PUFA, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, although the levels of these FA in seston were quite similar between the two lakes. The higher levels of the essential ω3 PUFA in A. salinus in Lake Shunet may be an adaptive response of the animals to a vertical stratification of physico-chemical conditions and significantly higher salinity levels at the boundary of adjacent bottom layer in this lake.     

Respiratory Levels and Adaptations in Four Freshwater Species of Gammarus (Crustacea: Amphipoda)

Respiration of four freshwater species of the amphipod crustacean Gammarus: G. fossarum, G. lacustris (river and lake), G. pulex and G. roeseli were measured in a closed, stirred respirometric chamber with a micro-electrode. Oxygen consumption, expressed as weight-specific oxygen uptake (R_s) in relation to decreasing oxygen concentration, varied at air saturation from 0.86 (G. lacustris, lake) to 2.06 μl O₂ mg⁻¹ AFDW h⁻¹ (G. pulex). R_s also differed intra-specifically among the two populations of G. lacustris. G. lacustris (river), G. pulex and G. roeseli expressed moderate ability to regulate their oxygen consumption at decreasing oxygen concentrations, whereas the regulation ability was higher in G. lacustris (lake) and in G. fossarum, which maintain high oxygen uptake at oxygen levels >2 mg O₂ l⁻¹. All four Gammarus species are partial regulators in response to variations in oxygen concentration. The differences between species are considered too small to account for their natural distributions. It appears that the tolerances of Gammarus species to organic pollution depend only in part on oxygen conditions.     

Distribution and ecology of freshwater sponges in Connecticut

A survey of Connecticut lakes and rivers revealed the presence of 7 species of freshwater sponge: Spongilla lacustris, Ephydatia muelleri, Eunapius fragilis, Anheteromeyenia ryderi, A. argyrosperma, Corvomeyenia carolinensis, and Corvospongilla novaeterrae in order of decreasing frequency of occurrence. Corvomeyenia carolinensis has not been reported previously beyond its type locality in South Carolina. In addition, microscleres of Spongilla lacustris, Anheteromeyenia-like megascleres, Ephydatia muelleri-like megascleres, and smooth megascleres (amphioxeas), which could not be assigned to a particular species, were found in surface sediments from lake cores. Spongilla lacustris inhabiting small rivers produced brown, thick-capsuled gemmules during the summer and yellow, thin-capsuled gemmules during the fall. The thick-capsuled gemmules, but not the thin-capsuled gemmules, are tolerant of desiccation; and populations of Spongilla lacustris and Ephydatia muelleri survived severe drying of their habitats during the summer.     

Selective feeding of Arctodiaptomus salinus (Copepoda, Calanoida) on co-occurring sibling rotifer species

1. Using two‐ and three‐dimensional video recordings, we examined the steps involved in predation that lead to the differential vulnerability of three sympatric rotifer sibling species (Brachionus plicatilis, B. ibericus and B. rotundiformis) to a co‐occurring, predatory, calanoid copepod (Arctodiaptomus salinus). 2. Brachionus rotundiformis, the smallest prey tested, was the most vulnerable with the highest encounter rate, probability of attack, capture and ingestion, and the lowest handling time. 3. Comparison of our results with those of a previous study shows that A. salinus is a more efficient predator than a co‐occurring cyclopoid copepod (Diacyclops bicuspidatus odessanus) feeding on these same rotifer species. However, despite its higher capture rates, A. salinus seems to be less selective than D. b. odessanus based on attack distances and prey handling times. 4. The differential vulnerability to both calanoid and cyclopoid copepod predation can help explain the coexistence and seasonal succession of these co‐occurring rotifer species.     

The effect of heated effluent on the occurrence and the reproduction of the freshwater limpetsAncylus fluviatilis Müller, 1774,Ferrissia wautieri (Mirolli, 1960) andAcroloxus lacustris (L., 1758) in two Dutch water bodies

The discharge of cooling water favours the occurrence of freshwater limpets. Reproduction ofAncylus fluviatilis is stimulated by the higher temperature of the cooling water; the life cycle ofFerrissia wautieri (nearly exclusively found in the outlet areas) does not, however, differ from that under natural temperature regimes. ForAcroloxus lacustris this is not clear as detailed studies on the life cycle under natural temperature circumstances are lacking. Acroloxus lacustris andFerrissia wautieri could be found in large numbers on hard substrates (stones), as well as on plant material in sheltered as well as in exposed situations. In this respect they differ fromAncylus fluviatilis, which is restricted in its occurrence to hard substrates and exposed situations.It is not very clear whether the occurrence ofAncylus fluviatilis is also influenced by some form of competition for food byBithynia tentaculata; both feed on diatoms. Further experimental studies of this question should yield interesting results.The changes in numbers of the three freshwater limpet species are mainly due to reproduction and migration, both largely governed by temperature and day length.It was possible to reconstruct the influence of cooling water in the Bergumermeer area by means of the ratio between the numbers ofAcroloxus lacustris andFerrissia wautieri. The share ofFerrissia was highest near the outiet and decreased with the distance from this station.     

Genetic divergence of three freshwater isopod species from southern New Zealand

Aim We examined the biogeography of three freshwater isopod species (Austridotea annectens, A. lacustris, A. benhami), and tested the hypotheses that genetic differences would: (1) exist between geographic locations; and (2) correspond to known geological events (e.g. appearance of islands leading to the availability of habitat). Location Southern New Zealand, including South Island, Stewart Island, Campbell Island and Chatham Islands. Methods We examined specimens throughout the known species range from 12 populations of A. lacustris, five populations of A. annectens, and three populations of A. benhami, using mitochondrial DNA (cytochrome c oxidase I) sequence analyses. Results We resolved three main clades corresponding to the three species, with 16% sequence divergence between A. annectens and A. benhami, and 31% divergence between these species and A. lacustris. Divergence within A. benhami was < 2.0%. However, divergence within A. lacustris reached up to 10% with four main groupings: (1) Chatham Islands; (2) Campbell Island; (3) Fiordland; and (4) east coast South Island and Stewart Island. Divergence within A. annectens reached up to 4.4%, with two main groupings: (1) Chatham Islands and (2) east coast South Island and Stewart Island. Patterns of genetic divergence were most likely the result of geographical isolation among A. lacustris and A. annectens populations. In particular, the divergence of A. lacustris and A. annectens on Chatham Islands may correspond to the availability of this habitat c. 4 Ma, whereas the divergence of A. lacustris on the much older Campbell Island and in Fiordland may indicate either a rare founder event or a change in ocean circulation that resulted in their isolation from a once more widespread gene pool. Main conclusions The three New Zealand species of Austridotea are genetically distinct, with up to 31% divergence between species. Genetic variability was highest between populations of the two most widely distributed species, and divergence was greatest on islands distant from mainland New Zealand and in the discrete Fiordland region. The magnitude of genetic divergence of isopods on the Auckland and Chatham Islands is consistent with these populations having been founded in the Pliocene via oceanic dispersal from mainland New Zealand.     

Phytoplankton diet of Arctodiaptomus salinus (Copepoda, Calanoida) in Lake Shira (Khakasia)

A flow-through method was employed to study the algal part of the diet spectrum of the calanoid Arctodiaptomus salinus in the surface layer of the lake and in the phytoplankton biomass maximum zone (10 m deep). Daily consumption rates of this calanoid differed markedly in these layers, being 1 and 11 g ind ^–1 d^–1, respectively. The cyanobacterial taxa, Lyngbya contorta and Microcystis sp., accounted for more than a half of the ration. Nevertheless, the negative Ivlev electivity coefficient indicated that Arctodiaptomus prefers none of these two taxa. The low measured uptakes suggest that the energy expenditure is compensated by other resources, presumably microzooplankton and detritus.     

Distribution of Gammarus lacustris Sars (Amphipoda, Gammaridae) in Lake Shira (Khakasia, Siberia) and laboratory study of its growth characteristics

Spatial distribution of Gammarus lacustris in Lake Shira and growth of young specimens that feed on lake biota were studied. The amphipods have been shown to inhabit the littoral, sublittoral and the upper aphytal zones of the lake on stony-sandy soil and silted sand. The young and adult individuals stay apart. The young live in submerged or semi-submerged vegetation in the littoral, the adults in the sublittoral and upper aphytal zones. Maximum density of amphipods was encountered in the areas influenced by human activity.The feeding experiments revealed that the lake plankton is a more important food source for G. lacustris than any other food species. The specific growth rate measured was 0.039 d^–1, with a length increment 0.095 mm d^–1.     

The ecology of Synchaeta kitina Rousselet in Loch Leven,Scotland

Synchaeta kitina Rousselet reached population densities of up to 5000 ind.l^–1 in Loch Leven, between January 1977 and December 1982. The species was found over the entire range of temperatures recorded (0.4–21.4 °C), but was most abundant at temperatures above 7 °C. Embryo development times, determined under laboratory conditions, ranged from 122 h at 2 °C to 12.5 h at 20 °C. There was a marked inverse relationship between populations of S. kitina and Daphnia hyalina var. lacustris in the loch. It seems unlikely that this was due to interference competition from Daphnia. S. kitina can be cultured on Rhodomonas minuta var. lacustris and there is some evidence that this rotifer also feeds on small flagellates in its natural environment.     

Trophic interactions and benthic animal community structure in the Colorado River, Arizona, U.S.A.

1. Cladophora glomerata is the dominant filamentous green alga in the tailwaters of the Colorado River, U.S.A., below Glen Canyon Dam, but becomes co-dominant with filamentous cyanobacteria, Oscillatoria spp., below the confluence of the Paria River (26km below the dam) where suspended sediments are elevated. 2. Benthic algal assemblages played an important role in the distribution of the amphipod, Gammarus lacustris, in the dam-controlled Colorado River through Grand Canyon National Park, Arizona. Cladophara and G. lacustris showed a weak positive relationship at ten cobble-riffle habitats in the Colorado River from Lees Ferry (25km below the dam) to Diamond Creek (362km downstream), while no relationship was found between Oscillatoria and G. lacustris. 3. The relationship between algal substrata and G. lacustris was tested by a series of in situ habitat choice experiments. G. lacustris showed a significant preference for Cladophora (with epiphytes) over Oscillatoria spp., detritus and gravel in treatment pans at Lees Ferry. 4. Epiphytic diatoms (i.e. food) were the overriding determinant of subtratum choice by G. lacustris in laboratory experiments. Gammarus chose the Cladophora/epiphytic diatom community over sonicated Cladophora with few diatoms. The amphipods also chose string soaked in diatom extract over string without diatom extract. 5. Importance of mutualistic interactions in aquatic benthic community structure is discussed.     

Thermal stress defense in freshwater amphipods from contrasting habitats with emphasis on small heat shock proteins (sHSPs)

This study comparatively evaluated small heat shock proteins (sHSP) (related to α-crystallin) and antioxidant enzymes such as peroxidase (POD), catalase (CAT), glutathione S-transferase (GST) as anti-thermal stress response in two contrasting freshwater amphipods, the stenoecious Baikalean endemic Eulimnogammarus cyaneus and the Palearctic Gammarus lacustris.The thermal stress modulated the activity of antioxidant enzymes as well as the sHSP synthesis in both species. In both species, only the declining POD activity showed a clear dependency on exposure time.The most expressed response to elevated temperatures has been the activation of sHSP synthesis, with clear differences in the patterns: in G. lacustris, sHSP concentrations peaked after 12 h with a subsequent decline, while they increased steadily in E. cyaneus. Hence, the stenoecious species did not acclimate to the thermal stress within the given exposure time as the euryecious did.     

Habitat Characteristics of Eurytemora lacustris (Poppe, 1887) (Copepoda,Calanoida): The Role of Lake Depth,Temperature,Oxygen Concentration and Light Intensity

Field observations, laboratory experiments and a literature survey were conducted to evaluate the habitat characteristics of Eurytemora lacustris (Poppe 1887), a freshwater calanoid copepod species. Combined effects of temperature and oxygen concentration in the deep water of thermally stratifying lakes seem to be the ultimate factors governing the occurrence of the species throughout its home‐territory. E. lacustris is largely restricted to relatively deep lakes (>30 m) providing a hypolimnetic refuge characterised by low temperatures (<∼10 °C) and oxygenated water during summer. Therefore, although the species is spread over much of Europe it was only found in a small number of lakes. Long‐term records in different lakes revealed E. lacustris to be perennial with relatively high biomasses occurring from May to September. During thermal stratification on average 87% of the nauplii and 72% of the copepodite biomass was found in hypolimnetic waters colder than 10 °C. Diurnal vertical migration was observed for the copepodid stages, but the migration amplitude clearly decreased from May to September. The migration amplitude was significantly related to light intensity. According to its special habitat requirements, E. lacustris might be considered a glacial relict sensitive to temperature increase and oxygen depletion. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of temperature,food and individual variability on the embryonic development time and fecundity of <Emphasis Type="Italic">Arctodiaptomus salinus</Emphasis> (Copepoda: Calanoida) from a shallow saline pond

Organisms living in temporary and shallow wetlands are adapted to survive in very fluctuating and unpredictable conditions and might help us to understand life cycle strategies and plasticity in the context of global warming. Despite the importance of Arctodiaptomus salinus in these systems, little is known about the effect of temperature on its population dynamics. Through an individual-based experimental protocol, we studied the effect of this factor and food on its reproduction. This approach has revealed a large range of variability in reproductive parameters in all the experimental conditions. Temperature positively affected egg production and negatively longevity, but did not affect clutch size. Under unsuitable food conditions, the clutch size decreased and the inter-clutch period increased, and when the food conditions improved, the number of eggs increased gradually in every clutch. Eggs from the same clutch hatched synchronously. In contrast, there were significant differences between the hatching times of clutches from different females and between those of the same female. The observed individual variability increased when temperature moved away from the medium values. The thermal tolerance threshold for A. salinus development might be around 25–29°C. Since water pond is close to this thermal limit for long periods of time, an increment of temperature because of global warming might have dramatic consequences on this population. The individual-based experimental approach of this study provides useful information to construct realistic individual-based models, which will help us to better understand the population-level consequences of individual variability in A. salinus reproduction.     

Proteomics of proteins associated with astaxanthin accumulation in the green algae <Emphasis Type="Italic">Haematococcus</Emphasis> <Emphasis Type="Italic">lacustris</Emphasis> under the influence of sodium orthovanadate

An extensive proteomics analysis has identified proteins associated with astaxanthin accumulation in the green algae Haematococcus lacustris under oxidative stress induced by sodium orthovanadate (SOV). Measurement of total carotenoid accumulation per cell biomass showed an increase from 81 to 136 pg/cell after being exposed to 2.5 mM SOV, when compared to the control cells at day 3 of cultivation. A total of 83 proteins were differentially expressed in SOV-treated H. lacustris in comparison with control cells. They consisted of 34 down-regulated and 49 up-regulated proteins. Of these, 17 highly-expressed proteins were analyzed by MALDI-TOF-MS to identify the function of the differentially expressed proteins in response to oxidative stress in H. lacustris.     

Seasonal Divergence of Bosmina Morphs

Seasonal occurrence and vertical distribution of two sympatric Bosmina morphs were investigated in two oligotrophic, deep fjord-type lakes. Bosmina obtusirostris and B. lacustris displayed similar ecology, but B. obtusirostris exhibited more eggs per clutch. B. obtusirostris is probably the most viable of the two morphs when fish predation is relaxed, while B. lacustris exhibits an advantage with increasing fish and invertebrate predation. This has important consequences for habitat selection of the two morphs. B. obtusirostris and B. lacustris are most probably two phenotypes of a polymorphic species.     

Respiration of Cytherissa lacustris (Ostracoda) at different temperatures and its tolerance towards temperature and oxygen concentration

Summary The ostracod species Cytherissa lacustris was investigated with respect to its temperature and oxygen tolerance limits. In laboratory experiments the tolerance limits were found to be much wider than expected from field data. Hatching of first instars was observed in cultures up to 20° C. The tolerance limit for oxygen concentrations was less than 1 mg O₂·l^-1 at 10° C and 20 h exposure. The distribution pattern of C. lacustris along a depth profile in lake Attersee showed a maximum density between 10 and 20 m depth coinciding with temperatures between 4 and 15°C throughout the year. The size dependence of respiration rates of well adapted C. lacustris is within the normal range of small metazoans. Its weight specific rates of oxygen uptake indicate an adaptation plateau in the range between 10 and 15°C. Possible reasons and advantages of such an adaptation for C. lacustris are discussed.