Production de CO2 à l'interface air-mer. Une approche par l'étude des phénomènes respiratoires dans la microcouche de surface. CO2 Production at the Sea-Air Interface. An Approach by the Study of Respiratory Processes in Surface Microlayer

Sea-surface microlayer and underlaying water samples were collected in the Bay of Marseilles (France) in order to study respiratory activity of microneuston and its possible influence on respiratory CO₂ production. Three methods were tested: Biochemical Oxygen Demand (BOD) as an estimation of community respiration, Electron Transport System activity (ETS) and ¹⁴C-Glucose uptake monitored by ¹⁴C-CO₂ liberation. BOD and ETS data clearly showed enhanced respiratory activities (up to 310 μl O₂/l/h) in surface-films as compared to underlaying waters; moreover the slope of the linear regression between these data led to R/ETS value of 0.689 and provides evidence for the presence of an important heterotrophic fraction within the microneuston. Though ¹⁴C-Glucose measurements showed only a slight trend for higher total activity (incorporation + respiration) in surface microlayers, significant enhancement of relative ¹⁴C-CO₂ production giving rise to CO₂ diffusion across air-water interface was observed.     

Influence de quelques paramètres du milieu d'incubation sur la survie d'alevins de saumon atlantique,Salmo salar L., en ruisseau expérimental. Influence of some Environmental Parameters upon Survival during Embryonic Development of Atlantic salmon,Salmo solar L., in an Experimental Stream Channel

The effect of some environmental parameters of the redd (substrate composition, interstitial dissolved oxygen concentration) upon survival of Atlantic salmon embryos was studied in a large artificial stream channel. Batches of 3000 eyed eggs were buried 0.25 m deep in the gravel substrate of 8 different channel sections, where natural or artificial sediment deposition took place. Upon emergence, fry were captured in drift nets or by electrofishing. Survival varied from 32 to 94 % in the different sections. It was strongly affected by volume of sediment less than 10 mm in particle size and more particularly by the fraction less than 0.2 mm, the main component of natural sediment deposition. Survival was less strongly determined by oxygen concentration variations except for values less than 2 mg/l obtained in the section with highest sediment deposition. Available volume of interstitial void space appeared to be crucial for good survival during larval development.