Diversity and Vulnerability of Larval Recruitment and Metamorphosis Strategies in Mediterranean Fish (M/F)

Job Description

Thesis Subject

Most marine fish exhibit a two-phase life cycle: pelagic drifting larvae followed by juveniles and adults living in coastal habitats. The return of larvae to the coast, their settlement, and survival in this habitat constitute larval recruitment. This process is accompanied by extensive morphological, physiological, and behavioral changes, primarily regulated by thyroid hormones: this is the larva to juvenile metamorphosis. This ecological and developmental transition, critical for population renewal, is particularly sensitive and threatened by climate change and pollution.
Endocrine disruption is a major pathway through which environmental stressors - such as marine heatwaves and chemical pollution - impair the development of marine organisms. Pioneering studies on a few coral fish species have shown that altered thyroid signaling, following exposure to thermal or chemical stress, can compromise the morphological, pigmentary, or behavioral transformations essential for juvenile survival after larval recruitment. However, these studies remain limited to a small number of species, mostly tropical, and do not allow for an assessment of the diversity of metamorphosis strategies and their differential vulnerability to environmental stressors in other ecological contexts, particularly along the Mediterranean coast.
This PhD project aims to address this gap by adopting a comparative and integrative approach across multiple non-model Mediterranean species. Its objectives are:
1. Characterize the diversity of metamorphosis and larval recruitment strategies by quantifying their morphological, pigmentary, and behavioral determinants (using standardized and automated quantitative analyses via high-resolution imaging, video tracking, and deep learning).
2. Analyze the dependence of metamorphosis and larval recruitment strategies on thyroid hormone (TH)-controlled endocrine pathways, using functional approaches combining hormone dosing and treatments, as well as gene expression measurements (qPCR and transcriptomics).
3. Assess the vulnerability of metamorphosis and larval recruitment strategies (via the aforementioned biomarkers) to chemical and thermal stressors (metals, pesticides, heatwaves), to identify mechanisms leading to impaired larval recruitment success in certain species following exposure to multiple, isolated, and combined stressors (ecotoxicological bioassays in controlled environments).
By studying how the diversity of larval recruitment and metamorphosis strategies modulates the resilience of young fish to anthropogenic pressures, this thesis will contribute to predicting the effects of global change on the dynamics of coastal fish populations.

Your Work Environment

The PhD student (M/F) will join the EcoEvoDevo team under the supervision of M. Marc Besson, at the Biologie Intégrative des Organismes Marins (BIOM) laboratory, a Unité Mixte de Recherche (UMR7232) CNRS-Sorbonne Université (SU) on the Observatoire Océanologique de Banyuls-sur-Mer campus.
This thesis is part of the ANR FRAMES (01/2026-12/2029) project, which aims to study the diversity and vulnerability of larval recruitment and metamorphosis strategies in marine fish. The ANR FRAMES project brings together 2 faculty researchers, 4 engineers, and 1 zootechnician, resulting from a collaboration between BIOM and the Service Mutualisé d'Aquariologie (SMA) from the Observatoire Océanologique de Banyuls-sur-Mer. This provides diverse expertise, operational and technical support, and ultimately an environment conducive to the development of the integrative and interdisciplinary approaches required for this thesis.
Professional training will be required and must be completed as soon as possible after recruitment:
- Training as an applicator or designer in animal experimentation with aquatic models
- Certificat d'Aptitude à l'Hyperbarie (CAH) (Class 0B minimum, Class 1B preferred)

Constraints and risks

Some tasks will be carried out in a rearing and experimentation unit (confined environment, wet areas) and outdoors (coastal and marine zones). The role requires adaptation to constraints related to the study models (shifted schedules, possible on-call duties on weekends and holidays) and the demands of working in confined and outdoor environments.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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