Some factors effecting algal densities in a eutrophic farmland stream

Summary Population dynamics of attached algae in a eutrophic farmland stream (Wellow Brook, England) were correlated through multiple regression analyses with changes in 7 physico-chemical parameters (temperature, light, water velocity, pH, NO₃–N, P₂O₅–P, SiO₂–Si). Samples were taken every 2 weeks for 25 consecutive months between June 1973 and June 1975. The relative significance of the 7 parameters in controlling densities varied widely depending on species. Overall light was most important, accounting for 28 and 17% of density changes in the epipelon and epilithon respectively. While winter flooding caused a sharp reduction in the density of these 2 communities, the concentration of P₂O₅–P and NO₃–N and pH usually had little effect on numbers. The 7 parameters did not exert major control over the epiphyton, normally accounting for <30% of densities variation. Grazing by the protozoan Frontonia acuminata may have significantly reduced the density of the epipelon for 2 months during the spring but otherwise was of no importance to any community.     

Benthic algal biomass and productivity in high subarctic streams,Alaska

Year-round measurements of the standing crop of epilithic algae (as chlorophyll a concentration) in two streams — one second and one fourth order (map scale 1:63 360) — in interior Alaska (64°–65° N) were only about one tenth that reported from streams of temperate North America. Cell densities in these streams, however, were similar to those in comparable temperate streams. Year-round domination of the benthic flora by very tiny diatoms (Achnanthes spp.) may explain the apparent disparity between low chlorophyll a content and nearly average cell densities. Chlorophyll a standing crop in a more alkaline groundwater-fed stream, however, was higher and within the range of similarly sized temperate streams. Maximum chlorophyll a standing crop varied positively with alkalinity in 5 clear-water streams where standing crop was measured on natural or artificial substrates. Seasonal mean concentrations of sestonic chlorophyll a (used as estimates of benthic algal chlorophyll a standing crop) varied directly and significantly with alkalinity among ten clear-water streams; and, with total phosphorus among 8 of 10 clear-water and 5 brown-water streams studied. During the summer, when there is little darkness, gross primary productivity (as estimated by the diurnal dissolved-oxygen method) was similar to that of northern temperate streams. Gross primary productivity was also seen to vary directly with alkalinity in 5 clear-water streams of this region.U.S. Fish and Wildlife Service     

Some factors influencing the density of subarctic populations of Bosmina longirostris,Holopedium gibberum,Codonella cratera and Ceratium hirundinella

Changes in the density of 2 populations of Bosmina longirostris, Holopedium gibberum and Codonella cratera were correlated through multiple regression analyses with shifts in temperature, light, nannoplankton densities and seston weight. Sampling took place every 2 weeks between June 1975 and November 1976 in the Yellowknife River and Yellowknife Bay, both in the Canadian subarctic. Temperature was usually the main factor influencing all 3 species, accounting for up to 60% of the seasonal variability in B. longirostris, 37% in H. gibberum and 62% in Codonella cratera. Seston (the major food source) ranked second overall and in one instance accounted for 60% of density changes in B. longirostris. Nannoplankton were consumed in only small numbers and had little influence on densities. Light was of minor importance to all species. Temperature was also the main factor effecting reproduction and feeding in B. longirostris and H. gibberum (the only species studied). The simultaneous collections of Ceratium hirundinella made in the river and bay indicated that temperature accounted for 30–55% of the seasonal variability of this species, followed by light (4% and nutrients (3–4%).     

Species composition and biomass of an epipelic algal community in a subarctic lake before and during lake fertilization

The species composition, biomass (measured as algal volumes) and chlorophyll concentration of epipelic algae was studies before (1977) and during (1978–1979) fertilization with phosphorus and nitrogen of Lake Gunillajaure, a small subarctic lake in northern Sweden.
The epipelic biomass, dominated by Cyanophyceae and Bacillariophyceae, was high (5.6–20.1 cm³ m⁻²) at all depths in the lake with the highest values in the hypolimnion (8–13.7 m). Calculated over mean depth it was 20 times higher than that of the phytoplankton. There was no significant increase in biomass during fertilization and neither did the species composition change. The chlorophyll concentration on the other hand were significantly higher in late 1978 and in 1979 which was probably an effect of the declining light climate caused by a large phytoplankton development in the lake. Constant seasonal biomass and species composition indicate a perennial epipelic community in this lake.     

Size relationships of Acroneuria californica (perlidae,plecoptera) and its prey

Summary Acroneuria californica has a life cycle of three years and nymphs of quite different sizes were present throughout the year. The annual cycle of feeding habits is described. Diptera were heavily consumed in summer and Trichoptera in winter. Ephemeroptera were a regular component of the diet with minor peaks in spring and late summer. A positive relationship is shown between the size of stonefly nymphs and their prey of three insect orders. A size-dependent relationship is also shown in the qualitative nature of the diet. Trichoptera were eaten by large nymphs, Ephemeroptera by those of intermediate size and Diptera by the smallest nymphs. Interactions between prey size and seasonal availability are discussed.

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Zusammenfassung Acroneuria californica hat einen dreijährigen Lebenszyklus, und Nymphen von ganz verschiedener Grösse waren anwesend während des Jahres. Der jährliche Zyklus der Nahrungsgewohnheiten ist beschrieben. Im Sommer wurden Diptera bevorzugt, im Winter Trichoptera. Ephemeroptera waren ein regulärer Teil der Nahrung mit kleinen Spitzen im Frühling und im Spätsommer. Ein positives Verhältnis ist aufgezeigt zwischen der Grösse von Nymphen und ihrer Beute von drei Insektenordnungen. Ein grössenabhängiges Verhältnis ist auch aufgezeigt in der qualitativen Art der Nahrung. Trichoptera wurden von grossen Nymphen verzehrt, Ephemeroptera von mittleren und Diptera von den kleinsten. Die Wechselwirkung zwischen Grösse der Beute und jahreszeitlicher Verfügbarkeit wird diskutiert.

     

Sediment-to-water blue-green algal recruitment in response to alum and environmental factors

The sediment-to-water recruitment of blue-green algae was investigated in a shallow lake following treatment with aluminum sulfate and sodium aluminate to control sediment phosphorus (P) release. A comparison of results from two summers each before and after treatment indicates that the treatment did not universally impact the recruitment of either sporulating or non-sporulating forms of blue-green algae. Blooms of Anabaena, Aphanizomenon, and Coelosphaerium resulted predominantly from growth in the water column following strong recruitment episodes lasting up to two weeks, while Microcystis populations were relatively insensitive to periodically high inputs from recruitment. The development of planktonic populations of Gloeotrichia echinulata, by contrast, were largely dependent on sustained recruitment in response to adequate light and temperature regimes at the sediment surface.The cellular P content of recruited G. echinulata colonies was unaffected by the accumulation of aluminum floc to the lake sediments. Both G. echinulata and C. naegelianum showed elevated levels of cellular P in newly recruited colonies as compared to planktonic colonies, indicating P transport from the sediments to the water column. Total P translocation by blue-green algae was negligible in the absence of a substantial recruitment of G. echinulata. The recruitment of G. echinulata, and hence the magnitude of P translocation, was therefore more responsive to environmental conditions prevalent at the sediments than to direct effects of the treatment itself.     

Relocation,consolidation, and settlement pattern in the Canadian subarctic

The relocation and consolidation of subarctic native populations into settlement patterns designed according to southern, urban models has often resulted in cultural confusion and an increase in interpersonal tension, alcohol abuse, and violence. Through a review of selected case material, and the detailed examination of one relocated community, the dynamics of this situation are highlighted. Where native communities have re-established themselves beyond the reach of government planners, the recreation of more culturally appropriate settlement patterns has ensued.     

The ecology of pre-imaginal simuliidae (Diptera) in South-East Queensland,Australia

A study of the pre-imaginal simuliid fauna of South-East Queensland was conducted to elucidate some of the aspects of their ecology. A total of 17 species of three genera (Cnephia, Austrosimulium and Simulium) bred in the area. The highest diversity of species was found to occur in mountainous areas near the coast which had the following conditions: high rainfall, steep relief, cool temperatures, on the edge of forests with streams of the order 1–3 (using a 1 : 250,000 map).More detailed studies of A. bancrofti, S. nicholsoni and S. ornatipes were made to investigate microdistribution, colonization, drift, pupation timing and population changes. Current velocity was the most important factor determining the distribution of A. bancrofti, while the distribution of S. nicholsoni was influenced by a preference for vegetation substrate and current velocity. Late instar larvae of A. bancrofti and S. ornatipes occurred in faster currents than early instar larvae. Pupae of these two species primarily occurred on the downstream side of submerged substrates. Colonization of a particular stream was dependent on the oviposition preference of gravid females while drift, looping, or descent on silk threads was used for larval dispersal from the oviposition site. Early instars of A. bancrofti drifted from quiet reaches of mature rivers to rapids, while S. ornatipes larvae appeared to be more sessile with limited dispersal from site of egg masses. Drift occurred throughout 24 hours with little change in total numbers. Early instars of A. bancrofti however showed a definite diurnal tendency while the proportion of late instars increased at night. Pupation of S. ornatipes was diurnal under undisturbed conditions. The larvae of A. bancrofti and S. nicholsoni both developed in the Brisbane River system, however the populations of A. bancrofti peaked in late winter, a dry season with stable water conditions while S. nicholsoni larvae were most abundant from late summer, at the end of the rains to the early winter. The larvae of S. ornatipes, which occur in small streams down to temporary trickles, were most numerous during the warm rainy period.Department of Parasitology, University of Queensland     

Hydrogen evolution as a consumption mode of reducing equivalents in green algal fermentation

Dark anaerobic fermentation in the green algae Chlamydomonas MGA 161, Chlamydomonas reinhardtii, Chlorella pyrenoidosa, and Chlorococcum minutum was studied. Our isolate, Chlamydomonas MGA 161, was unusual in having high H₂ but almost no formate. The fermentation pattern in Chlamydomonas MGA 161 was altered by changes in the NaCl or NH₄Cl concentration. Glycerol formation increased at low (0.1%) and high (7%) NaCl concentrations; starch degradation, and formation of ethanol, H₂, and CO₂ increased with the addition of NH₄Cl to above 5 millimolar in N-deficient cells. C. reinhardtii and C. pyrenoidosa exhibited a very similar anaerobic metabolism, forming formate, acetate and ethanol in a ratio of about 2:2:1. C. minutum was also unusual in forming acetate, glycerol, and CO₂ as its main products, with H₂, formate, and ethanol being formed in negligible amounts. In the presence of CO, ethanol formation increased twofold in Chlamydomonas MGA 161 and C. reinhardtii, but the fermentation pattern in C. minutum did not change. An experiment with hypophosphite addition showed that dark H₂ evolution of the Escherichia coli type could be ruled out in Chlamydomonas MGA 161 and C. reinhardtii. Among the green algae investigated, three fermentation types were identified by the distribution pattern of the end products, which reflected the consumption mode of reducing equivalents in the cells.     

Ecophysiological differences among Leymus mollis populations across a subarctic dune system caused by environmental, not genetic, factors

Plant species that persist during succession, from the colonization to the stabilization stages, face major environmental changes. Such changes are believed to have significant effects on species performance. In subarctic coastal dune systems, Leymus mollis colonizes the embryo dunes, on the upper limit of the beach. It reaches its maximum density on the foredune, but also grows on older, stabilized ridges. This paper reports on the phenotypic variations of some ecophysiological traits associated with the persistence of L. mollis on a dune system on the east coast of Hudson Bay (northern Quebec). Leymus mollis ramets tend to have a lower net carbon assimilation rate and water use efficiency, and a higher substomatal CO₂ concentration on the stabilized dune than on the foredune. However, these physiological differences cannot be explained by differences in leaf morphology or nitrogen content. Under controlled conditions, ecophysiological differences observed in the field disappear, suggesting that these are not genetic but determined by environmental changes along the foredune-stabilized dune gradient. We propose that higher net carbon assimilation rate on the foredune might be related to higher sink strength in relation to the growth-stimulating effect of sand burial.     

Effects of live coral,epilithic algal communities and substrate type on algal recruitment

The recruitment of algae is a critical process during algal colonization and invasions, including coral-to-algal phase shifts. Although algae are widely assumed to colonize and kill corals, there is very little known about the recruitment dynamics of coral reef algae. This study tested the ability of two dominant macroalgae (Fucales including Sargassum spp. and Lobophora variegata) to settle and grow on healthy coral tissue. The study also explored the effects of interactions with prior occupants, and of abiotic substrate properties (texture, and ceramic and carbonate material). The results indicate that healthy corals were able to prevent attachment or survival of recruits of these macroalgae. This is a significant point, since it suggests that the replacement of corals by algae may often require prior stress or death in the coral tissue. Pre-conditioning of plates at different sites had some effects, but these were relatively minor, whereas there was considerable variation within sites. Some of this variation appeared to be related to the amount of turf algae or crustose coralline algae on the plates. Recruitment was generally, but not always, higher on plates with rougher texture. Overall, this preliminary exploration indicates considerable potential for variability in outcomes of algal colonization, with implications for the dynamics of algal invasions. In particular, the results do not support suggestions that planktonic algal propagules can directly settle on and colonize healthy coral tissue.Communicated by Topic Editor D. Barnes     

Regional and hierarchical perspectives of thermal regimes in subarctic, Alaskan lakes

1. We examined 60 clear, stained and glacial lakes in Alaska to quantify the relative importance of climate setting, morphometry, transparency, and lake typology influences on various thermal characteristics including duration of growing season, water temperature, mixing depth (MD) and heat content. We used analysis of variance (ANOVA ) to test for differences in thermal characteristics in association with lake type and employed simple and multiple regression techniques to determine functional relationships between variables. 2. Latitude accounted for 60% of the total variance in length of growing season. Although the date of maximum heat content was consistent among lake types, stained lakes had longer growing seasons compared with clear and glacially turbid lakes. 3. Maximum water temperatures were approximately 3 °C higher in stained lakes and 3 °C lower in glacial lakes compared with clear lakes. Mean water column temperature was significantly lower in glacial lakes (5.9 °C) compared with clear lakes (7.4 °C), but there was no statistical difference between clear and stained lakes (7.2 °C) or between stained and glacial lakes. Maximum surface temperatures were positively related (r²=0.51) to colour (humic stain), but negatively related (r²=0.40) to inorganic turbidity (glacial silt). 4. Only about half of the lakes in our data set underwent summer stratification. None of the glacial lakes developed a distinct thermocline, but stained lakes had shallower MDs (mean 8 m) than clear lakes (mean 12 m). Thus, the MD to total depth ratio for glacial lakes was unity compared with mean values of 0.66 for clear lakes and 0.34 for stained lakes. Fetch explained a significant fraction (51%) of the total variance in MD. Considering all lakes, MD was inversely related to transparency (Secchi depth). In contrast, considering only stratified clear and stained lakes, MD was positively related to Secchi depth (SD), the fraction of the total variance explained was 23%. The sign of the slope was dependent on the mixture of lake types. 5. Despite significant (ANOVA ) differences in water temperatures, growing season, and MDs among the three lake types, there were no statistical differences in the summer heat budget associated with lake type. In addition, heat budgets were poorly correlated with lake area, depth and volume. In contrast, mean water column temperature was strongly and inversely related (r²=0.77) to mean depth. 6. Potential explanations for the similarity in summer heat budget among lake types and weak correlation with morphometry were attributed to different patterns in vertical heat distribution associated with lake typology (colour and turbidity) differences. 7. Multiple linear regression including climatic (latitude and altitude), morphometric, and lake typology (colour and turbidity) factors demonstrated a hierarchical (climate–morphometry–typology) regulation of growing season characteristics, water temperatures, stratification and heat retention. A regional and hierarchical framework for lake thermal characteristics adds to our understanding of potential responses to climatic change and may be important for regional management objectives for fisheries.     

Environmental factors influencing soil testate amoebae in herbaceous and shrubby vegetation along an altitudinal gradient in subarctic tundra (Abisko,Sweden)

Shifts in community composition of soil protozoa in response to climate change may substantially influence microbial activity and thereby decomposition processes. However, effects of climate and vegetation on soil protozoa remain poorly understood. We studied the distribution of soil testate amoebae in herbaceous and shrubby vegetation along an altitudinal gradient (from below the treeline at 500 m to the mid-alpine region at 900 m a.s.l.) in subarctic tundra. To explain patterns in abundance, species diversity and assemblage composition of testate amoebae, a data set of microclimate and soil chemical characteristics was collected. Both elevation and vegetation influenced the assemblage composition of testate amoebae. The variation was regulated by interactive effects of summer soil moisture, winter soil temperature, soil pH and nitrate ion concentrations. Besides, soil moisture regulated non-linear patterns in species richness across the gradient. This is the first study showing the effects of winter soil temperatures on species composition of soil protozoa. The effects could be explained by specific adaptations of testate amoebae such as frost-resistant cysts allowing them to survive low winter temperatures. We conclude that the microclimate and soil chemical characteristics are the main drivers of changes in protozoan assemblage composition in response to elevation and vegetation.     

Smoking, green tea consumption, genetic polymorphisms in the insulin-like growth factors and lung cancer risk

Insulin-like growth factors (IGFs) are mediators of growth hormones; they have an influence on cell proliferation and differentiation. In addition, IGF-binding protein (IGFBP)-3 could suppress the mitogenic action of IGFs. Interestingly, tea polyphenols could substantially reduce IGF1 and increase IGFBP3. In this study, we evaluated the effects of smoking, green tea consumption, as well as IGF1, IGF2, and IGFBP3 polymorphisms, on lung cancer risk. Questionnaires were administered to obtain the subjects' characteristics, including smoking habits and green tea consumption from 170 primary lung cancer cases and 340 healthy controls. Genotypes for IGF1, IGF2, and IGFBP3 were identified by polymerase chain reaction. Lung cancer cases had a higher proportion of smoking, green tea consumption of less than one cup per day, exposure to cooking fumes, and family history of lung cancer than controls. After adjusting the confounding effect, an elevated risk was observed in smokers who never drank green tea, as compared to smokers who drank green tea more than one cup per day (odds ratio (OR) = 13.16, 95% confidence interval (CI) = 2.96-58.51). Interaction between smoking and green tea consumption on lung cancer risk was also observed. Among green tea drinkers who drank more than one cup per day, IGF1 (CA)(19)/(CA)(19) and (CA)(19)/X genotypes carriers had a significantly reduced risk of lung cancer (OR = 0.06, 95% CI = 0.01-0.44) compared with IGF1 X/X carriers. Smoking-induced pulmonary carcinogenesis could be modulated by green tea consumption and their growth factor environment.