Conditions d'acceptation ou de rejet des valeurs obtenues apres denombrement de virus ou bacteries sur milieux de culture solides

Enumeration of viruses or bacteria on solid culture media does not ever give statistically acceptable results. When counting is impossible, we must do it again. For accepting or not the counting, the authors established some probability Tables (95% and 99%) according to microbial densities.     

Strategies for determining soil-loss tolerance

Excessive soil losses due to erosion or lateral displacement by machinery impair productivity. Some soil loss is tolerable, but not so much that plant productivity diminishes. Thus productivity is the dominant concern in determining soil-loss tolerance. The effects of soil loss on productivity, however, are difficult to determine. Therefore, two alternatives are discussed for determining the limits of soil loss, or soil-loss tolerance. These alternatives are the maintenance of soil organic matter and, for shallow and moderately deep soils, the maintenance of soil depth. They are not new strategies, but our rapidly increasing knowledge of the dynamics of soil organic matter and the rates of soil formation from bedrock or consolidated sediments warrants the reconsideration of these alternatives. Reductions in either soil organic matter or the depth of shallow or moderately deep soils will lead to declining productivity. Soil organic matter, considered to be a surrogate for productivity, is much easier to monitor than is productivity. Also, there are many computer models for predicting the effects of management on soil organic matter. Recently compiled data on rates of soil formation suggest that soil losses of 1 t/a (2.24 Mg/ha yr) are greater than the rate of replenishment by the weathering of lithic or paralithic material in all but very wet climates.     

Industrial pollution discharges from the West African region

Information on the type and quantity of industrial pollutants from major land-based sources entering the marine environment through direct coastal discharges or indirectly through rivers, as well as on the present status of industrial waste management (treatment and disposal) practices, are provided for the West African region. Most of the data utilized in this analysis were collected by six UNIDO experts who visited the eighteen countries of the West African region during the period of January through August 1980. Industrial operations were visited and information was collected from the various ministries involved with industrial development and environmental protection. Estimates of the mass of pollutants discharged to the ocean were based upon production rates used in conjunction with actual measurements made by the industries located in the countries visited; studies reported in the literature; and an extrapolation of the U.S. Environmental Protection Agency Effluent Standards for various industrial sectors. The West African region was divided into five zones closely approximating the major currents of the Atlantic Ocean. The estimated pollution discharged by the industrial sector was calculated for each of the zones by adding the contribution from each country assigned to a zone.     

Herbivory by the myctophid fish Ceratoscopelus warmingii

During a study of midwater fish feeding in the oligotrophic North Pacific gyre in August 1978, nine specimens of a tropical-subtropical myctophid, Ceratoscopelus warmingii, were found to have been feeding on mats of diatoms, Rhizosolenia spp. Chemical analyses of the intestinal contents of several additional specimens showed significantly elevated levels of diatom degradation products. Therefore, C. warmingii, although known to feed on zooplankton, appears to be adapted for occasional herbivory. Such an adaptation is exceptional within a major ecological group of oceanic fishes that was previously thought to be exclusively carnivorous. Like omnivorous and herbivorous fishes in general, C. warmingii has a longer intestine than other myctophid species. As an adaptive response to competition from a diverse fish fauna in a low-productivity environment, occasional herbivory by C. warmingii runs counter to the theoretical expectation by expanding rather than narrowing the range of potential food types.     

Size-related selection of two intertidal gastropods by the reef crab Ozius truncatus

Reef crabs, Ozius truncatus H. Milne-Edwards 1834, and gastropods, Bembicium nanum (Lamarck, 1882) and Nerita atramentosa Reeve, 1855, were collected from a South Australian rocky intertidal platform in April 1981. Laboratory experiments were conducted to determine (1) the size of prey chosen, and (2) the energy gained by the reef crabs feeding on B. nanum and N. atramentosa. The time taken to break open and consume prey increased exponentially with prey shell height. Crabs with larger master claws had shorter handling times for a given prey size. When offered a range of prey sizes, crabs selected prey of a certain size, well below the maximum prey size that they could handle. The mean prey size selected by crabs did not concide with the size predicted to yield the maximum rate of energy gain. For example, one reef crab preferred B. nanum 5 to 8 mm in size, but the size class predicted to yield the greatest energy gain was 4 to 4.9 mm. The results of the laboratory prey-choice experiments are discussed in relation to the shore-level size gradients of B. nanum and N. atramentosa.