General information
Job title: Thesis in ecology of aquatic environments (M/F)
Reference: UMR7362-JEABEI-001
Number of positions: 1
Work location: THONON LES BAINS
Publication date: Monday, September 22, 2025
Type of contract: Fixed-term contract Doctoral student
Contract duration: 36 months
Thesis start date: November 3, 2025
Workload: Full
Remuneration: The remuneration is a minimum of €2,200.00 per month
Section(s) CN: 29 – Biodiversity, evolution and biological adaptations: from macromolecules to communities
Description of the thesis subject
From Individual to Ecosystem: Growth, Filtration, and Ecological Impacts of the Quagga Mussel, an Invasive Engineer Species, in Lake Geneva
Background
Zebra and quagga mussels (Dreissena polymorpha and D. rostriformis bugensis) are two sessile bivalves of the family Dreissenids that have invaded a wide range of freshwater ecosystems worldwide. Although extensive research has been conducted on the zebra mussel for several decades, significant knowledge gaps remain regarding the biology, ecology, and impacts of the quagga mussel on aquatic systems. This knowledge gap can be attributed to the earlier introduction and rapid spread of the zebra mussel, while the quagga mussel invasion progressed more slowly and arrived much later in Western Europe, only in 2011 in France. Today, the quagga mussel is recognized as one of the most aggressive invasive freshwater species, with profound ecological and economic consequences. The proliferation of the quagga mussel poses a significant threat to biodiversity. Today, its relatively recent establishment in large peri-Alpine lakes, such as Lake Geneva, combined with its high colonization potential, raises many concerns, both ecological and economic. From an ecological perspective, filtration induces a cascading change in the trophic functioning of the lake while its high epibenthic densities modify the habitat conditions for macroinvertebrates.
PhD subject
To determine the impact of the filtration activity of the quagga mussel on the biodiversity and functioning of Lake Geneva, it is necessary to know its quantitative importance (density, biomass) which is directly linked to some of its physiological capacities (e.g. its growth, reproduction, speed and colonization capacity, etc.). It is also interesting to evaluate the effects of changing habitat quality on benthic macroinvertebrates. As part of this thesis, the doctoral student will have the following missions:
– 1. to evaluate the growth rates of the bivalve throughout a year and for a variety of environments (e.g. depths, habitats). This evaluation will make it possible to propose a first precise model of the animal’s growth;
– 2. to update the mapping of the bivalve distribution at the lake scale, in terms of density, biomass and biovolume. This map will be the basis for an evaluation of the theoretical global filtration capacity at the ecosystem scale;
– 3. to evaluate the impact of the quagga mussel on the benthic macroinvertebrate compartment.
To this end, the work that will have to be carried out is as follows:
– 1. participate in monitoring the distribution of the bivalve carried out within the framework of the International Commission for the Protection of Lake Geneva Waters and related projects. The doctoral student will carry out:
o mussel counting, distinguishing the quagga from the zebra mussel;
o measurements of sizes, biomasses, volumes;
o mapping of age structures, densities and biomasses;
o modeling of an overall filtration capacity at the lake scale, filtration being biomass-dependent and different according to the age structure.
– 2. analyze a collection of images taken by diving or by ROV. The doctoral student will carry out:
o estimation of growth rates from image analyses by comparison with in situ controls;
o calculation of a growth model as a function of environmental parameters (eg, temperature, depth);
o analysis of the three-dimensional evolution of aggregates.
– 3. study the impact of the quagga mussel on other biological compartments. The doctoral student will carry out, depending on the time allocated to this item:
o a bibliographic synthesis on the invertebrates of Lake Geneva and other peri-alpine lakes and how the presence/absence of the quagga impacts them (benthification and/or trivialization processes).
o the potential refuge zone effect that river mouths would constitute, by comparative analysis of the in situ benthic fauna of these spaces with those adjacent invaded by the quagga;
o targeted colonization experiments of aggregates of different qualities placed in natura (e.g. artificial substrates imitating gravel banks, shell beds, mussel beds) by comparison with plots manipulated in terms of habitat quality.
The strategy and means put in place to obtain this data and carry out these different tasks are/will be the following:
– For mapping: participation in the existing model and reflection on its improvement or an alternative model.
– For the measurement of individual sizes: caliper measurements for sampling and photogrammetric analyses for underwater aggregates;
– For the measurement of density and biomass: measurements then extrapolation to the sample; extrapolation to the scale of the lake;
– For the theoretical calculation of filtration: modeling based on the results of experiments carried out by another doctoral student (second thesis proposed within the framework of the ANR QUALAG, co-supervised by the ENES-CARRTEL laboratory in Saint-Etienne) who will test the effects of temperature and different environmental conditions.
– For the measurement of individual growth: photogrammetry with dedicated software; analysis of the existing image bank and new data;
– For the selection and marking of deep aggregates (ROV): protocol to be defined with the doctoral student and participation in the acquisition.
– For the analysis of invertebrates associated with the aggregates: sorting then determination of individuals with a binocular magnifying glass, microscopy, metabarcoding.
Work context
The thesis is part of a project called QUALAG and supported by the French National Research Agency (ref 25-CE02-1280, https://qualag.hub.inrae.fr/). Led by StĂ©phan Jacquet (INRAe), the overall project aims to (i) better assess the distribution and dynamics of the quagga mussel population, in terms of density, size and age structure; (ii) determine its growth rates and the population’s filtration capacity in response to key environmental factors; and (iii) use these results to initiate a model for assessing the mussel’s potential impacts on the functioning of Lake Geneva. The main part of the project team works in Thonon-les-Bains at the INRAe hydrobiological station. The doctoral student (M/F) will spend most of their time there and will carry out missions in Strasbourg, at LIVE, for part of the data exploitation and valorization.
The LIVE, Image, City, Environment Laboratory (UMR7362) is an interdisciplinary laboratory that includes the “Biodiversity and Ecological Processes (BIOECO)” team, which brings together ecologists. Their research questions aim to limit the erosion of biodiversity in different contexts, including ecosystems invaded by exotic species. The doctoral student (M/F) will be attached to this team.
Constraints and risks
Driving license B
