Factors controlling the growth of field populations of Hydrodictyon reticulatum in New Zealand

Since Hydrodictyon reticulatum was introduced to New Zealand it has spread rapidly and produced persistent annual nuisance growths in areas where nuisance algal had not occurred previously. Field bioassays were conducted at 10 sites between August 1993 and February 1995 to evaluate the seasonal growth patterns and the factors controlling growth under natural conditions. H. reticulatum exhibited a strong seasonal growth pattern with growth rates up to 0.33 doublings d^-1 from August to March, are duction in growth rate in April and little or no growth from May to July. The H. reticulatum present in New Zealand has are latively low requirement for dissolved inorganic nitrogen (DIN) in comparison with other nuisance species, with its growth rate being saturated at 200 mg m^-3. This and the high affinity for DIN as shown by a K_s of 29 mg m^-3 have been key factors in the establishment of nuisance growths of H. reticulatum in New Zealand. This revised version was published online in August 2006 with corrections to the Cover Date.     

Some features of feeding,respiration and energy conversion of Dapnia Magna

Some results of studies with Daphnia magna are presented. These results can be used as background information for toxicologists, but the techniques referred to might well be used for toxicity tests. Daphnia magna is a filter-feeder. With the Coulter Counter it was shown that the feeding mechanism is aselective for size of the food particles. It was also shown that algal cells can pass the gut of Daphnia magna several times before being completely digested. The uptake of food is proportional to the food concentration up to a critical concentration. Above this concentration the food uptake is constant. Respiration is also dependent on the food concentration, and has a maximum value at food concentrations near the critical concentration of the feeding process. Growth efficiency is independent of the food concentration. The effect of temperature on the feeding process is different for low and high food concentrations. Growth efficiency is maximal at 10°C and above 22°C growth efficiency was negative, which means that the population cannot survive under the experimental conditions used, at temperatures above 22°C.     

Optimum Temperatures for Common Zooplankton Species in the White Sea

The optimum temperatures for common zooplankton species were calculated using the materials of long-term observations carried out in the White Sea by the Zoological Institute, Russian Academy of Sciences. For the calculations an original method was used to calculate the temperatures corresponding to the greatest density of plankton species (density-weighted). Two complexes of species have been distinguished comprising warm-water and cold-water species, respectively. Some differences in seasonal dynamics have been revealed between these two groups of species.     

Optimal temperature drop for the growth and development of young cucumber plants

The thermomorphological responses of young cucumber plants to a temperature drop lasting 2, 4 and 6 hours applied at the beginning, in the middle and at the end of the night were examined. Plant height, leaf petiole length and plant dry weight were measured and, based on the experimental data, the regression dependences of growth variables on the temperature drop were fitted. A method to determine the optimal temperature drop (the duration and time of exposure) which results in shortened plant height and leaf petiole length without a decrease in plant dry weight is proposed.     

Effets de la température sur la croissance de deux algues vertes du fleuve St-Laurent,secteur de Gentilly,Québec

Two abundant phytoplankters from the St-Lawrence river: Scenedesmus spinosus Chodat 1913 and Pediastrum boryanum (Turp.) Menegh (Chlorophyta, Chlorococca) were sampled, isolated and cultured in monospecific culture. Growth responses were measured after acclimation to different temperatures and after thermal shock treatments.Post-acclimation specific growth rates followed similar patterns with optimal temperatures at about 24°C (S. spinosus) and 26°C (P. boryanum). Final densities were much less influenced by temperature in S. spinosus than in P. boryanum. Post-treatment responses depended on the temperature level maintained after treatment rather than on treatment conditions. No treatment seemed to delay the exponential growth phase. The time needed to reach final densities corresponding to stationary growth phase was not influenced by any thermal treatment. In situ thermal effects at Gentilly nuclear site could be more severe, due to differences in time-temperature history experienced by the algae.

     

Une etude sur clarias senegalensis val. dans la region du lac kossou (cote d'ivoire)

A study on Clarias senegalensis Val. in the region of Lake Kossou (Ivory Coast). Clarias senegalensis is the dominant silurid of the man-made lake Kossou and some smaller impoundments in the same region. Comparison of data spread over a five year period starting from 1970, some months before the dam was completed, reveals that the density of C. senegalensis dropped to the original level that existed in the river after reaching a peak in the years following the damming. This phenomenon which coincides with the impoverishment of the lake waters, is explained by the fact that C. senegalensis has its optimal habitat in poorly oxygenated waters, rich in organic matter. It is able to colonize this kind of productive waters thanks to the suprabranchial organ. In these optimal conditions it mainly feeds on aquatic insects and plankton.The fecundity of C. senegalensis may reach 20o ooo ripening eggs per female. Reproduction occurs during the rainy season in flooded savannas. Growth rates are very high and the age determinations show that, in the region of Kossou, C. senegalensis reaches an average standard length of 620 mm (2.7 kg) within three years.Our results are compared to literature data on other related species of the genus Clarias and the position of C. senegalensis within this generic complex is discussed.

     

Thermal adaptation of Arctic charr: experimental studies of growth in eleven charr populations from Sweden, Norway and Britain

1. Experimental growth data for Arctic charr (Salvelinus alpinus L.), all fed on excess rations, from 11 European watercourses between 54 and 70°N were analysed and fitted to a new general growth model for fish. The model was validated by comparing its predictions with the growth rate of charr in the wild. 2. Growth performance varied among populations, mainly because of variation in the maximum growth potential, whereas the thermal response curves were similar. The estimated lower and upper temperatures for growth varied between ?1.7 to 5.3 and 20.8–23.2 °C, respectively, while maximum growth occurred between 14.4 and 17.2 °C. 3. There was no geographical or climatic trend in growth performance among populations and therefore no indication of thermal adaptation. The growth potential of charr from different populations correlated positively with fish body length at maturity and maximum weight in the wild. Charr from populations including large piscivorous fish had higher growth rates under standardised conditions than those from populations feeding on zoobenthos or zooplankton. Therefore, the adaptive variation in growth potential was related to life‐history characteristics and diet, rather than to thermal conditions.     

Exact age determination in laboratory and field-caught Drosophila

A method to prepare and count daily growth layers in internal thoracic muscle attachments is described. Growth layers have been observed in five species in the laboratory and in five field-caught species—including Drosophila melanogaster and D. pseudoobscura. The growth layers do not vary with the genetic make up of individuals within a species, and are comparable between individuals of different species. However, a daily temperature cycle is required for the production of strong layers in laboratory stocks.     

两品系蒙古裸腹溞种群补偿生长及适宜食物密度

研究了两品系蒙古裸腹溞(晋南品系和内蒙品系)继饥饿后的补偿生长及其生长发育的适宜食物密度。结果表明,两品系蒙古裸腹溞生长发育的最适食物——篕∏蛟迕芏染?50×104/mL。对两品系蒙古裸腹溞而言,饥饿0.5d的蒙古裸腹溞有全补偿生长,饥饿1~2d有部分补偿生长现象,饥饿超过3d已没有补偿生长。可以认为,蒙古裸腹溞仅在短时间饥饿时有补偿生长现象的发生。     

Seasonal variation in the thermal performance of juvenile Atlantic salmon (Salmo salar)

1. Experimental data on the maximum growth and food consumption of winter‐acclimatised Atlantic salmon (Salmo salar) juveniles from three Norwegian rivers situated at 59 and 70°N were compared with predictions from published models of growth and food consumption of summer‐acclimatised fish from the same populations. 2. All winter‐acclimatised fish maintained positive growth and a substantial energy intake over the whole range of experimental temperature (1–6 °C). This contrasted with predictions from growth models based on summer acclimatised Atlantic salmon, where growth and energy intake ceased at approximately 5 °C. 3. Growth and food consumption varied significantly among populations. Winter‐acclimatised fish from a Northern population had a higher mass‐specific growth rate, higher energy intake and higher growth efficiency than southern populations, which is contrary to predictions from models developed using summer‐acclimatised salmon, where fish from the Northern population had the lowest growth efficiency. 4. The experiment provides evidence that thermal performance varies seasonally and suggests adaptation to the annual thermal regime.     

Effect of Season on the Impact of Ecosystem Engineers in the New River, NC

The importance of biotic interactions in structuring communities can depend on seasonal changes in abiotic context. The crayfish and benthic-feeding fish of the headwaters of the New River have been shown to be ecosystem engineers due to their ability to reduce the amount of sediment accumulation in cobble beds during the summer. However, the temperature-driven seasonal reduction in the activity level of these organisms may reduce their impacts during the colder months. I measured the impact of benthic-feeding fish and crayfish on sediment accrual in the headwaters of the New River during the winter using a field exclosure experiment. I found that during the winter there was no effect of benthic-feeding fish and crayfish on the amount of sediment accumulating in cobble beds in the headwaters of the New River. These findings suggest that seasonal changes in the effect of ecosystem engineers need to be quantified for a complete understanding of the effect of these organisms.