Etudes expérimentalles sur la sensibilité du phytoplancton d'eau douce aux variations de salinité dans le fjord du Saguenay (Estuaire du St-Laurent), Canada Experimental Studies on the Susceptibility of Freshwater Phytoplankton to Variation of Salinity in the Fjord of Saguenay (St. Lawrence Estuary), Canada

The Saguenay Fjord is characterized by very high run-offs. The annual flow varies between 1.2 and 4.2 × 10³ m³ . s⁻¹. During the summer the surface salinity shows a sharp horizontal gradient (from 1 0/00 to 20 0/00). The surface phytoplankton, mainly freshwater and even some euryhaline species is submitted to salinity stress. Continuous culture experiments were conducted to study the susceptibility of this freshwater phytoplankton under different salinity conditions. Some pennate diatoms (dominant group) are found as relatively tolerant to salinity. Microflagellates have been found to be resistant to salinity up to 26 0/00. Chlorophyll concentrations and rates of primary production of those organisms are as high as those of the control.     

Influence de la spéciation du cuivre sur les populations phytoplanctoniques naturelles de la rivière du Saguenay,Québec,Canada Influence of Copper in Various Forms on Natural Phytoplanktonic Populations from the Saguenay River,Quebec, Canada

In 1981, experiments to study the toxicity of copper in its ionic, complexed (to humic acid) and adsorbed (on cellulose fibers from a local paper mill) forms on species composition, standing crop, and photosynthesis of phytoplankton were conducted in chemostats with natural aggregations composed mainly of either green algae or of diatoms from the Saguenay River. In the aggregations of green algae, the rates of primary production were more strongly inhibited by copper than were the chlorophyll a concentrations, whereas the cell numbers, standing crop and rates of primary production of the diatoms were all strongly inhibited by copper.     

Variabilité à court terme des propriétés physiques,chimiques et biologiques du Saguenay,fjord subarctique du Quebec (Canada)

Tidal variability of water mass characteristics has been assessed in the upper 100 metres of the Saguenay, a subarctic fjord in Québec, Canada. Temperature and salinity show a maximum variability in the 5-15 m layer in which vertical oscillations of a very sharp pycnocline are observed. Phosphates, nitrates and chlorophyll a are highly variable above this pycnocline during a tidal cycle, but dissolved oxygen content is remarkably stable in the whole water column. It is concluded that fluctuations of many variables in the subsurface waters might be large enough to hinder high rates of primary production.     

Nucléotides adényliques et assimilation photosynthétique du phytoplancton dans deux lacs du Massif Central français

Adenine Nucleotides and Phytoplanktonic Primary Production in Two Lakes in France The adenine nucleotides concentrations and photosynthetic assimilation of phytoplankton were established during two annual sampling seasons for two lakes with different nutrients concentrations (Lakes Pavin and Aydat). Intensive photosynthetic assimilation of phytoplankton led to a limited but real evolution of the pool of adenine nucleotides towards forms less charged with high energy phosphate bond (ADP and AMP). This evolution is seen as a consequence of the ATP hydrolysis in the process of cell biosynthesis.     

Population genetics of hereditary hemochromatosis in Saguenay Lac-Saint-Jean (Quebec, Canada).

Hereditary hemochromatosis (HH) is an autosomal recessive disorder that has a high prevalence in Caucasian populations. Based on HLA typing in 18 families, the gene frequency was estimated 0.12. The homozygote frequency was 0.014 and the heterozygote frequency was 0.21 in Saguenay Lac-Saint-Jean (SLSJ), a geographically isolated region of northeastern Quebec. The genealogical reconstruction showed that 15 of the 57 obligate carriers of the HH gene could be traced back to a unique ancestor in the 18th century. The mean coefficients of inbreeding and kinship were 17 and 15 times, respectively, higher in the HH group than in three control groups. The values of both coefficients were much higher than those found in other HH populations and in most of the other recessive disorders prevalent in SLSJ.     

Aspects toxiques du cuivre sur la biomasse et la productivité du phytoplancton de la rivière du Saguenay,Québec

In 1979 and 1980, batch culture experiments were conducted to observe the inhibitory effect of copper ion (concentrations of 10, 50, 100, 200 and 400 µg Cu · l^–1) on the standing crops and photosynthesis of phytoplankton of the Saguenay River (for 124 hours) and in Chlorella vulgaris (for 8 days). These algal assays were carried out using the surface water of the Saguenay River. In natural populatoins of phytoplankton, it was found that photosynthesis was more sensitive than growth: at the lowest concentrations, such as 10 µg Cu · 1^–1, copper seemed to increase the chlorophyll concentrations whereas the rates of primary production show a decrease of 60% with respect to the control. At higher concentrations of copper, the effect is weak in chlorophyll concentrations and more pronounced in the rates of primary production (decrease of 86 to 90%). The pennate diatoms are dominant (in all the samples) and these organisms are known as relatively resistant to copper. In Chlorella vulgaris, it was observed that with 100 µg Cu · 1^–1, chlorophyll concentrations and rates of photosynthesis respectively decrease by 63 and 99% with respect to the control. At higher concentrations of copper, a maximum decrease of 70% and 99% respectively for chlorophyll concentrations and rates of primaryproduction are observed.

     

Genetic structure of the Saguenay, 1852-1911: evidence from migration and isonymy matrices

The Saguenay is a region in northeastern Québec populated in the second half of the 19th century through migration from other parts of Québec. The present-day population of nearly 300,000 is the result of both immigration and high rates of intrinsic growth. This population has been of interest to geneticists because of the high incidence of certain hereditary diseases, notably spastic ataxia, tyrosinemia, agenesis of the corpus callosum, vitamin D-dependent rickets, and myotonic dystrophy. Parent-offspring migration and isonymy matrices were used to estimate random kinship using the Malécot model for six 10-year time periods from 1852-1911. Comparisons between two estimates of kinship--one from parent-offspring migration matrices (phi) and the other from isonymy (R)--and geographic distance were made using both product-moment and Mantel correlation. Comparisons of within- and between-subdivision kinship were made using nonparametric and Mantel correlation. Within-subdivision kinship from the phi matrix was also compared with kinship estimated from marriage dispensations for endogamous marriages. The estimates of random kinship from the parent-offspring matrices showed a good fit with geography. However, isonymy did not correlate well with geographic distance; and phi and R showed no correlation until the last two time periods, and the diagonal of phi did not correlate with the marriage dispensations. Examination of scatterplots of phi vs. R suggests that nonrandom migration during the process of settlement formation is responsible for the lack of correlation. While movement across space seems to be highly dependent on distance, nonrandom selection of migrants means that between-subdivision estimates of kinship based on migration are not congruent with those obtained by other methods. On the whole, genetic differentiation seems to have been low due to the high levels of movement between subdivisions and immigration. The weak dependence of genetic structure on geographic distances in the present population is demonstrated by mapping the geographic distribution of cases of three recessively inherited diseases.     

Aspects of winter primary production in the upstream section of Saguenay Fjord

From August 1985 to May 1986, experiments on primary production were carried out bi-weekly in the superficial waters (1–10 m) at one representative station (maximum depth of 260 m) located at the head of the Saguenay Fjord. During the winter season (January–March), the microalgal cells are abundant but their productivity is low. At the beginning of the snow-ice cover (January) the cells are mainly concentrated in the ice-cover interface and in the surface waters whereas in February–March, the cells are much more abundant in the ice. Results showed that the physico-chemical conditions are unfavourable for high productivity. The quantity and the quality of light under the ice cover are not the only factors limiting the photosynthetic activity of epontic community. The ice interior and epontic communities during the winter are mostly composed of the two euryhaline speciesAsterionella formosa andTabellaria fenestrata.     

Evolution of inbreeding coefficients and effective size in the population of Saguenay Lac-St.-Jean (Quebec)

We computed mean inbreeding coefficients (FIT, FIS, and FST) based on approximately 2,700 ascending pedigrees of contemporary people from Saguenay Lac-St-Jean (Québec, Canada). This allowed us to appreciate the accumulated inbreeding and to follow the evolution of these coefficients since the founding of Québec. One of the results was the expected increase in FST. Relying on this parameter, we computed the effective size (Ne) of the contemporary population, obtaining a value around 1,000, in agreement with previous estimations. We noticed a decrease of Ne through history despite the population's growing size.     

Caracteristiques du microphytobenthos d'un lac volcanique meromictique (Lac Pavin,France). I. Biomasse chlorophyllienne et déterminisme du cycle annuel

Characterization of the Microphytobenthos in a Volcanic Meromictic Lake (Lake Pavin, France). I. Chorophyll Biomass and Determination of the Annual Cycle The sediments in Lake Pavin are almost exclusively biogen. The fine fraction (≤ 40 μm). comprises 99% of these sediments, making them appear as very fine and fluid silt. Up to 85% of the microphytobenthos is composed of epipelic Bacillariophyceae. The benthos at the different depths studied (10 m, 20 m, 30 m, 40 m, 50 m, and 60 m). are colonized by characteristic populations of diatoms. Analyses of the sediments revealed high concentrations of pigments ( ≥ 1 mg/g dried sediment). Such high concentrations usually result from phytoplankton sedimentation. The deepest area of the lake, as expected, contains the highest concentation of accumulated pigment, while shallower locations are richer in active pigments.     

Fertilisation de communautés phytoplanctoniques. ii. cas d'un milieu eutrophe: upwelling des côtes du sahara espagnol

Experiments with nutrient enrichment of phytoplankton communities have been carried out on surface waters from the upwelling area off Cap Blanc — Cap Corveiro (Spanish Sahara).None of the control flasks showed phytoplankton development despite the large quantities of nutrient available: this may be due to the presence of an inhibitor in the upwelling waters. On the other hand, most of the enrichments stimulated the autotrophic production. On average, the best growth rates were obtained when a full medium minus Fe-EDTA was added; marked phytoplankton development also took place when a medium without vitamins, or silicates, or phosphates, was added. Lack of metallic compounds (other than iron) and nitrates limit the algal growth.The maximum amounts of chlorophyll a (25–30 mg/m³) are close to the maxima usually observed in this area. The productivity rate (biomass produced/nutrients used) is very high.     

Phytoplancton du lac Ichkeul (Tunisie): Composition,structure et activité photosynthétique Phytoplankton of Lake Ichkeul (Tunesia): Composition,Structure and Photosynthetic Activity

Phytoplankton evolution was established during a study carried out on lake Ichkeul (Tunisia) from January 1985 to June 1988. During this period, the flora, composed of 51 species is distributed principally between Diatomophyceae and Chlorophyceae. Succesional changes of phytoplankton were often unpredictable and characterized by populations with monospecific trend. Photosynthetic activity and the parameters A_opt and I_K were studied regularly along the year 1985 by oxygen method (GOLTERMANN , 1969). The relations between phytoplankton composition and photosynthetic activity were discussed.     

How do sinking phytoplankton species manage to persist?

Phytoplankton require light for photosynthesis. Yet, most phytoplankton species are heavier than water and therefore sink. How can these sinking species persist? Somehow, the answer should lie in the turbulent motion that redisperses sinking phytoplankton over the vertical water column. Here, we show, using a reaction-advection-diffusion equation of light-limited phytoplankton, that there is a turbulence window sustaining sinking phytoplankton species in deep waters. If turbulent diffusion is too high, phytoplankton are mixed to great depths, and the depth-averaged light conditions are too low to allow net positive population growth. Conversely, if turbulent diffusion is too low, sinking phytoplankton populations end up at the ocean floor and succumb in the dark. At intermediate levels of turbulent diffusion, however, phytoplankton populations can outgrow both mixing rates and sinking rates. In this way, the reproducing population as a whole can maintain a position in the well-lit zone near the top of the water column, even if all individuals within the population have a tendency to sink. This theory unites earlier classic results by Sverdrup and Riley as well as our own recent findings and provides a new conceptual framework for the understanding of phytoplankton dynamics under the influence of mixing processes.     

Development of phytoplankton in Lake Pääjärvi (Finland) during under-ice convective mixing period

The development of winter phytoplankton communities was studied in both shallow and deep areas of Lake Pääjärvi, southern Finland, during the final 2 weeks of winter ice cover. Phytoplankton was mainly composed of diatoms, cryptophytes and chrysophytes. The diatoms Aulacoseira and Rhizosolenia were always uniformly distributed with depth, initially probably due to mixing induced by heat flux from the sediment and later due to thermal convection. Motile Rhodomonas cryptophytes and Chrysococcus chrysophytes were most abundant near the ice showing that, despite their small size, they were partly able to resist mixing by convection. Their ability to stay in more illuminated water layers was reflected in net rates of increase about an order of magnitude higher than those of diatoms in the middle of the lake. Given the low temperatures and convection, the observed net rates of increase of motile taxa were very high compared to growth rates reported in the literature. The gradual increase in light availability following melting of ice led to a consistent increase in the abundances of major phytoplankton taxa irrespective of deep convective circulation. It is suggested that those algae most abundant at the time of ice break have a competitive advantage in the following open water conditions when nutrients are abundant but deep water circulation limits light availability. The results emphasize that in lakes which cool below the maximum density of water before freezing, apparently small differences in temperature and light conditions can cause important changes in the circulation patterns that impact on phytoplankton development.     

Multiple environmental controls on phytoplankton growth strategies determine adaptive responses of the N : P ratio

The controls on the ‘Redfield’ N : P stoichiometry of marine phytoplankton and hence the N : P ratio of the deep ocean remain incompletely understood. Here, we use a model for phytoplankton ecophysiology and growth, based on functional traits and resource‐allocation trade‐offs, to show how environmental filtering, biotic interactions, and element cycling in a global ecosystem model determine phytoplankton biogeography, growth strategies and macromolecular composition. Emergent growth strategies capture major observed patterns in marine biomes. Using a new synthesis of experimental RNA and protein measurements to constrain per‐ribosome translation rates, we determine a spatially variable lower limit on adaptive rRNA:protein allocation and hence on the relationship between the largest cellular P and N pools. Comparison with the lowest observed phytoplankton N : P ratios and N : P export fluxes in the Southern Ocean suggests that additional contributions from phospholipid and phosphorus storage compounds play a fundamental role in determining the marine biogeochemical cycling of these elements.     

Influence du substrat sur la répartition des Crustacés stygobies interstitiels du Haut-Atlas occidental

The interstitial stygobiont distributions of two rivers in the western High Atlas is analyzed in relation with sediment granulometry. Sixteen stations were sampled along the rivers N'Fis and Zat and their tributaries. Granulometry analyses were performed. Three grain size sediment types constitute the subterranean biotopes and reflect the local hydrodynamical conditions. The main rivers stations, which undergo frequent natural or human disturbances, are characterized by a high content of fine sediment; in contrast, tributaries stations show coarse and well-classified sediments due to more stable biotopes and more regular hydrological conditions. The 92 taxa group 28 stygobiontic species with 11 crustaceans species. PCA. based on 16 stations, three faunistic richness indexes and three granulometric factors display a high correlation between coarse grain-size content and the richness of stygobiontic taxa. A high silt content both limits the interstitial taxa and excludes crustaceans that occur only in coarse gravels. The granulometric preferenda in the species of the amphipod genus Metacrangonyx and isopods Microcerberus. Microcharon and Typhlocirolana are shown on Shepard triangular diagrams. Cohabitation of several species of the same genus could be explained by the occupancy of different ecological niches resulting from the grain-size proportion.     

PHOTOSYNTHESIS AND REGULATION OF RUBISCO ACTIVITY IN NET PHYTOPLANKTON FROM DELAWARE BAY1

Net phytoplankton (> 20 μm) comprised 51 ± 9% of the total chlorophyll (Chl) in a Skeletonema costatum– dominated spring bloom in Delaware Bay. The net phytoplankton had low C:N and high protein: carbohydrate ratios, indicating that their growth was nutrient-replete. Their photosynthetic responses were characterized by low specific absorption, low light-limited and light-saturated rates of photosynthesis, and high quantum yields, indicative of acclimation to low irradiance and internal self-shading. High fucoxanthin: Chi ratios also indicated low light acclimation, but high photoprotective xanthophyll: Chi ratios suggested a high capacity for photoprotective energy dissipation. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) could be activated and deactivated in response to changes in irradiance and was fully activated at the surface of the water column and fully deactivated in aphotic deep water. Maximum Rubisco activity was correlated with Rubisco content and bulk protein content of the phytoplankton and with light-saturated rates of photosynthesis measured in short (< 20-min) incubations. Long (60-min) incubations caused a decrease in the light-saturated rate of photosynthesis, possibly because of feedback limitation. While feedback limitation is unlikely to occur in the water column, it should be considered when estimating productivity in well-mixed waters from fixed light-depth incubations.     

Growth rate of alpine phytoplankton assemblages from contrasting watersheds and N‐deposition regimes exposed to nitrogen and phosphorus enrichments

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Syringe pumped high speed flow cytometry of oceanic phytoplankton.

BACKGROUND: Nanophytoplankton (2-20 microm) are less numerous than picophytoplankton (<2 microm) in the oceans but their biomass and production are comparable and sometimes higher. The accuracy of cytometry-based enumeration of phytoplankton ultimately depends on cell abundance and sample flow rate. Commercial flow cytometers in which sheath and core streams are driven by air pressure cannot produce sufficiently high, stable sample flow rate. The present study demonstrates the applicability of a syringe pump for flow cytometric enumeration of oceanic nanophytoplankton on two meridional transects across the Atlantic Ocean. METHODS: Commercially available syringe pumps were used to deliver live phytoplankton samples into a flow cell of standard flow cytometers (FACSort, FACSCalibur, BD) with increased flow rate of > 1.0 ml min(-) (1) compared to the normal air pressure sample delivery of < 0.1 ml min(-) (1). An auxiliary application of syringe pump flow cytometry for calibrating 0.5 microm bead concentration standards is also discussed. RESULTS: The results demonstrated that flow cytometry of samples injected at rates above 0.1 ml min(-) (1) is achievable and worthwhile. Counts of phytoplankton in air and syringe pumped samples agreed closely. Syringe pumping of samples offered a broader range of flow rates up to 0.8-1.0 ml min(-) (1) without detrimental effect on flow cytometric enumeration of cells. The increased number of coincidences at high flow rates led to an approximate 10% decrease of Cyanobacteria counts when the acquisition rate approached 1,000 particles s(-) (1), but seemed to have a lesser effect on counting rarer phytoplankton. The syringe pump flow cytometry allowed enumeration of phytoplankton groups at concentrations of 5-100 cells ml(-) (1), cell concentrations equivalent to those of Cyanobacteria in the twilight deep ocean. CONCLUSION: The proposed syringe pump modification of a FACS instrument represents a significant improvement for accurate enumeration of the less abundant phytoplankton and so gives better estimations of phytoplankton distribution and standing stocks.     

Nitrogen deposition and warming – effects on phytoplankton nutrient limitation in subarctic lakes

The aim of this study was to predict the combined effects of enhanced nitrogen (N) deposition and warming on phytoplankton development in high latitude and mountain lakes. Consequently, we assessed, in a series of enclosure experiments, how lake water nutrient stoichiometry and phytoplankton nutrient limitation varied over the growing season in 11 lakes situated along an altitudinal/climate gradient with low N‐deposition (<1 kg N ha^?1 yr^?1) in northern subarctic Sweden. Short‐term bioassay experiments with N‐ and P‐additions revealed that phytoplankton in high‐alpine lakes were more prone to P‐limitation, and with decreasing altitude became increasingly N‐ and NP‐colimited. Nutrient limitation was additionally most obvious in midsummer. There was also a strong positive correlation between phytoplankton growth and water temperature in the bioassays. Although excess nutrients were available in spring and autumn, on these occasions growth was likely constrained by low water temperatures. These results imply that enhanced N‐deposition over the Swedish mountain areas will, with the exception of high‐alpine lakes, enhance biomass and drive phytoplankton from N‐ to P‐limitation. However, if not accompanied by warming, N‐input from deposition will stimulate limited phytoplankton growth due to low water temperatures during large parts of the growing season. Direct effects of warming, allowing increased metabolic rates and an extension of the growing season, seem equally crucial to synergistically enhance phytoplankton development in these lakes.