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.     

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.     

Stabilité du polymorphisme électrophorétique de douze populations naturelles françaises de Drosophila melanogaster

L'évolution dans le temps du polymorphisme de 5 locus enzymatiques a été suivie pour 12 populations naturelles françaises de Drosophila melanogaster. La structure génétique de ces populations ne varie pas, ou peu, d'un automne à l'autre. La bonne résistance au froid des imagos et le fait que la période hivernale suive celle de l'explosion démographique de l'espèce en France, indiquent que les populations analysées ne doivent pas subir d'importantes réductions de leurs effectifs durant l'hiver, susceptibles d'entraîner une forte dérive génétique. Dans ces conditions, le maintien de la même structure d'une année à l'autre peut s'expliquer par le fait que les populations sont panmictiques.     

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.