Leptodora kindtii survival in the laboratory

Leptodora kindtii , a pelagic predatory cladoceran, suffers high mortality on transfer to laboratory, which makes the experimental work difficult. We investigated the causes of high mortality, using four variables: water volume, animal density, light intensity, and origin of water for culturing, i.e., water from native or a non-native lake. For the experiments we used Leptodora and water from Lake Loosdrecht and Lake Maarsseveen (The Netherlands). Water was found to be the most important factor; the animals did not necessarily do better in lake water from which they were collected. Water volume and animal density were of limited importance, and light intensity did not affect survival.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41752/1/10452_2004_Article_DO00000328.pd

Variance in isotopic signatures as a descriptor of tissue turnover and degree of omnivory

1. Diet analyses using C and N stable isotopes commonly focus on mean isotopic signatures; however, isotopic variance among individuals is likely to also contain useful information including details of omnivory. 2. Changes in isotopic signature as a result of dietary shifts are not instantly manifest in the isotopic signature of consumer tissues, but lagged over a period of time required for equilibration. Tissue turnover times have not previously been described in terms of variance in isotopic signature among individuals, and variance among individuals following equilibration with a constant diet is limited. 3. Temporal changes in d15N and d13C variance in juvenile European Sea Bass (Dicentrarchus labrax) muscle, heart and liver were monitored following a shift from a wild diet to two single-source diets administered under seminatural conditions in captivity. Exponential decay functions of the standard deviation of d15N and d13C among individuals were used to model changes in variance over time. 4. All tissues exhibited a similar rate of tissue turnover using variance. However, variance among individuals within tissue types differed once fishes were equilibrated with the laboratory diet. The coefficients of variation of d13C and d15N were smallest in muscle and greatest in liver and greater among sampling dates than within. 5. Analysis of d15N and d13C in different tissues will not therefore provide equivalent power to detect differences in diet or to track changes in patterns of omnivory. Analysis of omnivory should be restricted to variance from a single tissue type. Of the tissues considered here, white muscle is most appropriate for this purpose. 6. Variance estimates derived here provide minimum values expected for a highly specialist feeding population. Departure from these values can be used to describe the degree of omnivory within a population

The unique methodological challenges of winter limnology

Winter is an important season for many limnological processes, which can range from biogeochemical transformations to ecological interactions. Interest in the structure and function of lake ecosystems under ice is on the rise. Although limnologists working at polar latitudes have a long history of winter work, the required knowledge to successfully sample under winter conditions is not widely available and relatively few limnologists receive formal training. In particular, the deployment and operation of equipment in below 0 C temperatures pose considerable logistical and methodological challenges, as do the safety risks of sampling during the ice covered period. Here, we consolidate information on winter lake sampling and describe effective methods to measure physical, chemical, and biological variables in and under ice. We describe variation in snow and ice conditions and discuss implications for sampling logistics and safety. We outline commonly encountered methodological challenges and make recommendations for best practices to maximize safety and efficiency when sampling through ice or deploying instruments in ice-covered lakes. Application of such practices over a broad range of ice-covered lakes will contribute to a better understanding of the factors that regulate lakes during winter and how winter conditions affect the subsequent ice-free period