Production primaire dans les eaux de surface de la Méditerranée occidentale. Calcul de la production journalière

We have found a relationship between the net absorption of carbon at time t divided by the net absorption of carbon in 24 h (A_N(t)/A_N(24)) and the incubation duration after sunrise, in surface waters of the western Mediterranean sea. This ratio is quite similar whatever the sample location, the sample depth and the 24-h net-absorption level. Considering this result, we have established a correction factor which may be used to convert primary production rates obtained from incubation durations ≤ 24 h to daily rates (24 h dawn-to-dawn).     

Recherches hydrobiologiques dans les rivières du Congo oriental

Sans résumé     

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.

     

Biologie de Gammarus laticoxalis laticoxalis dans une rivière du Liban

The biology of a population of Gammarus laticoxalis laticoxalis living in a perennial, relatively constant temperature river in Lebanon is studied. Life cycle, fecundity, sex-ratio, body length and demography were followed for almost two years. The reproductive cycle shows no resting period with fecundity being highest during the rainy season as compared to dry summer months.

     

Variations spatiales et saisonnières de la structure de groupements macrobenthiques littoraux en climat froid

Spatio-temporal variations of macrobenthic community structure were studied in the littoral zone of the Saint-Lawrence River (Québec). Its thermal regime is characterized by steep seasonal gradients from April to November and by a long ice-cover period with formation of an icefoot. Six sites were sampled each season for one year. Temporal variations are less important than spatial variations. They are mainly seasonal and depend on emergence and recruitment periods and on migrations but there are also long-term variations. An increase of the mean diversity index of sites corresponds to an increase of seasonal variations of community profile and to a decrease of seasonal variations of organism abundance; it is explained by a better exploitation of benthic resources rather than by environment stability. Spatial variations of community structure depend mainly on vegetation abundance. There is no faunal zonation corresponding to the icefoot action. In sites where Gastropods are abundant, icefoot does not change community profile but it explains diminutions of density and of species diversity. Chironomids are little affected by this phenomenon.     

Qualité des eaux en milieu estuarien: Suivi annuel de critères physiques et chimiques dans les eaux de l'estuaire de la Loire

Chemical composition and physical parameters of waters from the Loire estuary were examined in 1981–1982 in order to assess water quality. It appears that riverflow is of first importance on suspended matter load, dissolved nutrient concentrations and oxygenation. The annual hydrological cycle is made of two periods. During the first one low riverflow, low nutrient concentrations, high suspended matter load and oxygen depletion are noticed. During the second one higher riverflows occur accompanied with increasing nutrient concentrations, decreasing turbidity and restoration of dissolved oxygen. Results indicate that annual inputs of dissolved nutrients attain 60 000 t a^–1 for nitrogen, 2 400 t a^–1 for phosphorus and 100 000 t a^–1 for silica. It is suggested that the high suspended matter loading (¹ million t a^–1) is a significant factor disturbing oxygenation and by the way limiting water quality within the estuary.

     

Facteurs contrôlant la production primaire dens deux rivières soumises a une forte réduction de débit

The effects of river diversion on phytoplankton primary production and biomass in the downstream part of two rivers were studied in relation to physical and chemical variables. These rivers, situated north of the 52nd parallel, are characteristic of oligotrophic systems with phytoplankton primary production less than 10.76 mg C m^–2 h^–1, chlorophyll -a lower than 3.0 mg m^–3 and biomass between 118–1007 mg m^–3. The decrease in flow favored the establishment of an algal biomass approximately two times greater then that present before diversion. This increase in biomass was associated in one river with an increase of 2.5 times of the mean primary production. In the other river the primary production per unit of surface area remained stable but increased when expressed by unit volume, due to a great decrease in underwater light penetration, consequence of inorganic particular matter increase.

---

Facteurs contrôlant la production primaire dens deux rivières soumises a une forte réduction de débit

     

Fluctuations des nutriments au cours de la marée sur les parcs Ostreicoles de la rivière Penze (Nord-Finistère)

The design and performance of a simple, community level ecotoxicological testsystem is reported. Samples of periphyton communities, established on artificial substratum in natural streams were used to study effects on photosynthetic activity in short-term experiments. Photosynthesis was measured as light-dependent oxygen evolution or as ¹⁴CO₂-incorporation. The variability in photosynthetic activity between samples collected at the same time, expressed as coefficient of variation, was ca 20%. The variation in sensitivity of periphyton photosynthesis as dependent on sampling season was less than threefold for the two long-chained aliphatic amines and the textile industry effluent studied. Effects of the amines on periphyton from five different streams were also investigated. The ratio between maximum and minimum values of sensitivity was 5.6. It is concluded that the variation in sensitivity between different periphyton communities is similar to or less than that observed for fresh-water algal species. Some advantages with regard to ecological realism of using periphyton communities as test systems are discussed.     

Fixation d'azote par les cyanobacteries dans les rizières du Mali

Résumé La fixation de l'azote par les cyanobactéries a été étudiée pendant un cycle végétatif dans trois rizières pluviales soudano-sahéliennes ne recevant pas d'engrais azoté. Lorsque l'illumination solaire est forte, et en l'absence de couvert végétal, l'activité réductrice de l'acétylène (ARA) présente deux maximums, en fin de matinée et au milieu de l'après-midi. Dans le cas d'une intensité lumineuse moyenne ou faible et d'une couverture dense, on constate un maximum unique en fin de matinée ou début d'après-midi. Au cours du cycle cultural, l'ARA présente deux maximums, l'un au moment du tallage, l'autre à maturation du riz. En ce qui concerne les cyanobactéries fixatrices, le premier maximum correspond à la prédominance d'espècesd'Anabaena, et le second à la prédominance d'espèces deCylindrospermum. Dans une des rizières étudiées, aucune forme fixatrice de l'azote n'a été observée. Plusieurs espèces hétérocystées non-fixatrices ont été identifiées. Des expériences en vases de végétation ont confirmé l'inhibition de TARA des cyanobactéries par les fortes intensités lumineuses. LesOscillatoria se protègent contre la lumière par phototactisme négatif (enfouissement dans le sol) et par un processus de photocinèse agrégative.

---

Nitrogen fixation by cyanobacteria in paddy fields of Mali

Summary Nitrogen fixation by cyanobacteria was studied during a cropping cycle in three rain paddy fields of Mali that had not received exogenous nitrogen. Under intense sunlight and in the absence of a crop canopy, the acetylene reducing activity (ARA) showed two maxima, at the end of morning and in mid-afternoon. With medium or low intensity of light and dense plant cover, a single maximum was observed at the end of the morning. In the course of the cropping cycle, ARA showed two maxima, at the tillering period and at crop ripening. In regard to the nitrogen-fixing cyanobacteria, the first ARA peak corresponded to the predominance ofAnabaena species and the second one to the predominance ofCylindrospermum species. No nitrogen-fixing forms were observed in one of the paddy fields studied. A number of heterocystic non-fixing species have been identified. Pot experiments confirmed the inhibition of ARA in cyanobacteria by high light intensity.Oscillatoria spp. are self-protected against light by negative phototactism and by a process of photokinetic agregation.

---

Fijación de nitrógeno por cianobacterias en arrozales de Malí

Resumen Le fijación de nitrógeno por cianobacterias se estudió, durante un ciclo vegetativo completo, en tres arrozales de tipo pluvial, en Malí, a los que no se aportó ningún abono nitrogenado. Cuando la intensidad de la luz solar es fuerte y en ausencia de cubierta vegetal la actividad reductora de acetileno (ARA) presenta dos máximos: el primero al final de la mañana y el segundo a media tarde. Con una intensidad luminosa media o baja y una cubierta vegetal densa se observó un único máximo al final de la mañana o principio de la tarde. Durante el ciclo del cultivo la ARA presenta dos máximos: el primero relacionado con el momento de formación de la espiga y el segundo con la maduración del arroz. En cuanto concierne a las cianobacterias fijadoras, el primer máximo corresponde a una predominancia de especies deAnabaena y el segundo a una de especies deCylindrosporum. En uno de los arrozales estudiados no se ha observado ninguna forma fijadora de nitrógeno. Se han identificado especies no fijadoras de nitrógeno aunque formadoras de heterocistes. La inhibición de ARA por fuertes intensidades luminosas se ha confirmado mediante experiencias en maceta. LasOscillatoria spp. se autoprotegen de la luz mediante fototactismo negativo (se entierran en el suelo) y gracias a un proceso de fotocinesis agregativa.

     

Faunistique et répartition longitudinale des Trichoptères dans une rivière salmonicole de basse montagne,en Belgique

Trichoptera have been studied in the drainage basin of the Flavion, a small calcium-ion rich low altitude trout river in Belgium. During a one-year investigation, 45 species, which represent one fourth of the recorded Belgian Trichoptera, have been collected. As a whole, the caddis larvae show a rather weakly defined zonation. Longitudinal distribution of closely related species is discussed from the standpoint of interspecific competition.

     

Approche sociologique de la dépression saisonnière hivernale (1re partie)

What image does society have of seasonal affective disorder? How does the media address the issue? How should we look at the self-diagnosis tread? The market for light therapy products has grown massively, and the assimilation of their effects into well-being is not without risks. We discuss some of the sociological aspects of this phenomenon, which have led to a number of clinical cases. Then, we offer different hypotheses about the effects of light. Finally, we explain how, in a society that overvalues the sun, some patients with mood disorders choose the winter’s lack of light to express their unhappiness.     

Action de la quinoline sur les mitoses de segmentation des eufs d'urodèles: le blocage de la centrosphère

Quinoline in saturated solution (0,46 M) progressively destroys spindle and astral fibers, beginning in the juxtacentromeric region; it blocks the centrosphere material around the centriole. Chromosomes are immobilized in equatorial position far off the blocked centrospheres and may undergo telophasic transformation into karyomeres. Diastema may be inactivated before mitosis. Centrospheres are first deprived of some fibers, then granular and more or less dissociated, last completely smooth and segregated into cortex and medulla. Breaks and recombinations of chromosomes may appear after a long while, when a brief action is interrupted. With less concentrated solutions monopolar mitoses and monopolar telophases (rosettes) are observed (1/8 saturated solution), then shortened bipolar mitoses (1/16 saturated). Qualitative differences between quinoline and colchicine actions are evident.     

Action de la «densonucléose» de Lépidoptères sur les mammifères

Summary The virus of Densonucleosis ofGalleria mellonella (Lepidoptera) is not virulent for mice and rabbits by inoculation and by feeding. Newly born mice are not contamined by intracerebral inoculation. These data are important for comparison of this virus with some Arthropod born viruses and for biological control.