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Spatial distribution of macrozooplankton was studied during spring in Lake of Geneva to evaluate the influence of abiotic (water temperature and stability, nutrients) and biotic (bacteria, chlorophyll a, fish biomass) factors on macrozooplankton distribution. Mapping and spatial analyses revealed that abiotic factors, as well as crustacean abundances, were structured along a gradient in the great lake basin. Chlorophyll a biomass, bacteria density, cyclopoid abundance, and fish biomass showed more patchy or inshore-offshore distribution patterns. Using canonical analyses, we determined the relative contribution of the spatial and environmental factors to the distribution of macrozooplankton species and of trophic groups based on herbivory and omnivory/carnivory. The distribution of macrozooplankton can be explained by small-scale variations and lake gradients in abiotic and biotic factors, with a dominant contribution of the abiotic factors. Water temperature and stability, as well as ammonium, are the main factors related to macrozooplankton distribution in Lake of Geneva during spring. Chlorophyll a biomass was also related to the distribution of cyclopoids. The canonical models explained 35-72% of the variance in the distribution of total crustaceans, species, and trophic groups. However, 28-65% of the macrozooplankton variance remained unexplained, which may be due to fine-scale variations in other environmental factors.

-The change in catches and mean size of one-year-old perch (Perca fluviatilis) in Lake Geneva was studied between 1957 and 2005, and related to trophic changes and average temperature. The status of Lake Geneva, assessed on the basis of total phosphorus concentrations, switched from being oligotrophic before 1960 to eutrophic, with total phosphorus concentration reaching nearly 90 µg L −1 in [1976][1977][1978][1979]. In response to management measures, the trophic status then returned to mesotrophy in the early 2000s. Zooplankton is the main food consumed by young perch, and quantities present (annual biovolumes of zooplankton) were recorded throughout the study period. The lake water temperature was also recorded. Data obtained from perch catches and perch spawns enabled eleven strong cohorts of perch to be identified. Strong cohorts dominated the stock for three years, until they were massively caught by fishermen. Yields have fluctuated widely, increasing rapidly until 1975, and subsequently decreasing, with an exceptional decline between 1976 and 1981. During the period 1977-1981, unfavourable climatic conditions in spring were probably the main cause of this fall in perch yields. For the other periods, perch yields and the mean size of one-year-old perch were significantly correlated with trophic parameters, total phosphorus concentration and zooplankton biovolume. Correlations are higher if only strong cohorts are taken into account. As a result of the re-oligotrophication process, perch growth has been progressively reduced, age at first maturity delayed and strong cohorts become less frequent; the mean size of 0+ individuals in strong cohorts is significantly smaller than in the other cohorts, suggesting a population density effect in the context of a limited supply of zooplankton. During the study period, trophic changes in Lake Geneva have had more impact on perch growth and yield than has temperature, since no significant correlation could be detected between water temperature and perch growth. Resour. 21, 401-410 (2008) sont prises en compte. Avec le processus de ré-oligotrophisation, la croissance des perches diminue, l'âge de la maturité sexuelle est retardé et les fortes cohortes sont plus espacées ; la taille moyenne des individus 0+ des fortes cohortes est significativement plus petite que celle des autres cohortes, traduisant un effet marqué de densité-dépendance vis-à-vis de la ressource limitée de zooplancton. Durant la période étudiée, les changements trophiques du lac Léman ont eu un effet plus marqué que la température sur la croissance et les captures de perches, puisque aucune corrélation positive n'a pu être mise en évidence entre la température de l'eau et la croissance ou les rendements de la pêche des perches.

Regression equations relating length to dry weight have been derived for the four larval instars of Chaoborus flavicans (Meigen) . A general equation, in which all instars are lumped, was also developed, but produces biased results outside a rather narrow central interval .The rate of increase, in terms of weight, is minimal in first instar larvae and maximal in fourth instar larvae, while the second and third instars are both intermediate and very closely related to one another.Three critical points have been defined, corresponding to body lengths at which a particular instar has to molt in order to be able to continue growing optimally .