Preliminary trophic network analysis of subalpine Lake Annecy (France) using an Ecopath model

Abstract

Lake Annecy is the second largest natural lake in France, with intensive commercial and recreational fisheries. However, there is limited knowledge of its trophic interaction. A preliminary Ecopath model was fitted to study the trophic interaction in the lake using the available data on most of the ecosystem compartments. Fourteen functional groups were used in the present analysis. Most of the consumers have ecotrophic efficiency from 0.3 to 0.6. The results show that flow from detritus is as important as flow from primary producers. The overall transfer efficiency of the system is 9.6. The primary production/respiration (P p /R) ratio, which is 3.253, shows that Lake Annecy's ecosystem is comparatively mature. The gross efficiency of fisheries is 0.001173. Catch trophic level and percentage of primary productivity required for catch show that fishery in Lake Annecy is stable. The values of ascendancy (31.2) and overhead (68.8) show the stability of the ecosystem. Mixed trophic analysis indicates that zoobenthos have a positive effect on most of the fish functional groups. This preliminary model can be helpful to pinpoint the gaps in the present knowledge about Lake Annecy. RÉSUMÉAnalyse préliminaire du réseau trophique du lac d'Annecy avec le modèle Ecopath Le lac d'Annecy est le second plus grand lac naturel de France avec une importante pêcherie commerciale et amateur. Toutefois les connaissances sur les interactions trophiques sont limitées. Le modèle Ecopath a été ajusté pour étudier les interactions trophiques dans le lac en utilisant les données disponibles sur la plupart des compartiments de l'écosystème. Quatorze groupes fonctionnels ont été utilisés dans cette analyse. La plupart des consommateurs ont une efficience écologique qui varie de 0,3 à 0,6. Les résultats montrent que le flux de détritus est aussi important que le flux des producteurs primaires. L'efficience globale du système est de 9,6. Le rapport production primaire/respiration (P p /R) de 3,253 montre que le lac d'Annecy est relativement mature. L'efficience brute de la pêcherie est de 0,001173. Le niveau trophique des captures et le pourcentage de la production primaire requis par ces captures montrent que la pêcherie au lac d'Annecy est stable. Les valeurs de l'« ascendancy » (31,2) et de l'« overhead » (68,8) montrent la stabilité du système. L'analyse trophique montre que le zoobenthos a un effet positif sur la plupart des groupes fonctionnels de poissons. Ce modèle préliminaire peut être utile pour mettre le doigt sur les lacunes dans les connaissances actuelles sur le lac d'Annecy.

Effects of temperature and food supply on the growth of whitefish Coregonus lavaretus larvae in an oligotrophic peri‐alpine lake

“…This capacity of the lake to sustain larval growth might result from the fact that the copepod community is largely supported by terrestrial carbon (Perga et al , 2009). Moreover, the relatively high recreational and commercial fishing pressure on several fish species, including C. lavaretus (Janjua & Gerdeaux, 2009), may also limit food competition.…”

Toward an ecological understanding of a flood-pulse system lake in a tropical ecosystem: Food web structure and ecosystem health

“…Comparatively, the CI and SOI indices were much lower than for Lake Ayame in Ivory Cost (0. 386,0.193), and Lake Annecy in France (0.258, 0.107) and slightly higher than Chinese lakes: Taihu (0.206, 0.042) and Bao'an (0.205, 0.058) (Janjua and Gerdeaux, 2009;Traore et al, 2008). High values of CI and SOI could reflect the high diversity of diet composition while low values indicate a linear food web pattern rather than a web-like structure.…”

Modelling physical and ecological processes in medium-to-large deep European perialpine lakes: a review

“…Both studies deal with Lake Annecy and used models implemented inside the Ecopath with Ecosim framework (Christensen et al, 1992). Janjua and Gerdeaux (2009) studied trophic interactions in Lake Annecy using 14 food-web functional groups. The resulting food-web parameters showed that Lake Annecy is a mature and relatively stable ecosystem.…”