Unprecedented changes in mollusc assemblages of the littoral zone in the two largest peri-Alpine French lakes since the last 4500 years
Changements sans précédents des assemblages de mollusques de la zone littorale de deux grands lacs péri-alpins depuis les derniers 4500 ans
Mouthon, J. ; Magny, M.
Type de document
Article de revue scientifique à comité de lecture
Affiliation de l'auteur
IRSTEA LYON UR MALY FRA ; LABORATOIRE DE CHRONO-ENVIRONNEMENT UMR 6249 CNRS UFR DES SCIENCES ET TECHNIQUES BESANÇON FRA
Résumé / Abstract
This paper presents changes in mollusc assemblages in the two largest peri-Alpine French lakes, i.e. Lakes Bourget and Annecy, in eastern France during the late Holocene. It is based on new mollusc data obtained in Lake Bourget (1) from three sediment cores spanning the late Holocene period and (2) from modern samples taken around 1930 and in 2001. These new results are compared with those obtained from the neighbouring Lake Annecy and published in a previous paper. Results show that the modern period is characterised by unprecedented changes in the mollusc assemblages in Lakes Bourget and Annecy over the last 4500 years. The main drivers of the observed changes may be related to (1) the recent arrival of native and exotic species, (2) the considerable regression of lacustrine macrophytes following increased anthropic pressure on these ecosystems from the 1940s onwards, and (3) modifications of the nature and quality of the fine littoral sediments of Lake Bourget, probably linked to the regulation of its water level. In addition, the arrival of new species has led to the creation of no-analogue communities, i.e. which consist of species that are extant today, but in combinations not found until now. As a result, a return to the initial state in terms of community structures is thus difficult to envisage. On the contrary, re-establishing the dominance of charophytes and thus the dominance of gastropods, characteristic of the littoral malacocenoses of the Holocene, is a conceivable objective. Nonetheless, the persistence and extension of the period of hypoxic hypolimnion associated with warmer winters expected in the northern hemisphere could affect the recovery process negatively.
Journal of Limnology, vol. 73, num. 1, p. 36 - 46