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Primary Research Papers Published 13, August, 2026 :

Bathymetric asynchrony in the reproductive dynamics of quagga mussel (Dreissena bugensis) in a deep lake

Autors :

Alexandre Levallois · Katherine Costil ·
Nadège Villain‑Naud · Stéphan Jacquet ·
Victor Frossard

Abstract :

Freshwater invasions by Dreissenidae have profoundly altered aquatic ecosystems worldwide. The quagga mussel, Dreissena bugensis, is particularly successful due to its ability to colonize deep, cold habitats in stratified lakes, yet the influence of depth on its reproductive dynamics and lake-scale recruitment remains poorly understood. Using histological analyses of gametogenesis, we investigated seasonal and bathymetric reproductive patterns of D. bugensis in Lake Bourget (France) over one annual cycle. Reproductive stages were quantified using a Mean Gonad Index (MGI). Littoral populations showed marked seasonality, with gonadal rebuilding from autumn to spring and a main spawning period between May and July. In contrast, deep populations exhibited delayed maturation, frequent gonadal resorption and prolonged coexistence of reproductive stages, resulting in reduced synchrony with shallow populations. Sex-specific patterns were also observed, with females reaching advanced maturity earlier and maintaining it longer than males, whose maturation appeared more episodic and temperature-dependent. We propose that bathymetric asynchrony in reproductive dynamics may generate successive spawning events along the depth gradient, contributing to the prolonged larval presence typically observed in invaded lakes. Incorporating depth-structured reproduction may therefore be critical for understanding lake-scale recruitment processes and invasion trajectories in deep lakes.