HAL Portal UPF (Université de la Polynésie française)
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On optimal transport with f-divergence regularization
No full textThis report establishes that an optimal transport (OT) problem regularized by a given f-divergence admits the same solution as another OT problem regularized by a different gdivergence, under an appropriate transformation of the cost function. This structural equivalence between OT problems regularized by distinct divergences, in the sense of sharing the same unique minimizer, is demonstrated within the framework of polish spaces with bounded cost functions. Under these general assumptions, the existence of optimal potentials for the dual problem and the uniqueness of the optimal coupling for the primal problem are rigorously established
Decline and status of natural pearl oyster (Pinctada margaritifera) stocks in two French Polynesia black pearl farming lagoons
No full textInternational audienceIn French Polynesia, the pearl oyster Pinctada margaritifera has allowed black pearl production since four decades. The production remains dependent on spat collections in atoll lagoons. Through their reproduction, the oysters of the natural stock are contributors of spats, and possibly the only contributor. After an assessment in 2013, natural stocks of Takaroa and Ahe atolls were revisited in 2022 and 2024 respectively. Results show a sharp decrease of the densities at almost all field sites, with average lagoon-wide losses by factors of 2.35 and 8.87 for Ahe and Takaroa respectively. Takaroa was impacted in 2013–2014 by a massive harmful phytoplanktonic bloom and the decrease was expected, but the population size structure shows recruitment, providing hope for farmers. Conversely, the reason for Ahe's population decline remains unclear. Likely suspects are increased periods of high temperature and predation that affect oysters at their different life stages and impact recruitment and survival
Différences de traitement entre titulaires et contractuels en matière de compléments de rémunération : pas de violation du principe d'égalité
No full textInternational audienceNote sous CE, 10 avril 2025, no 497615 (inédit au Lebon
Agent contractuel et reprise du travail à l'expiration d'un congé maladie non rémunéré : quelles obligations procédurales à la charge de l'administration ?
No full textInternational audienceNote sous CE, 16 juillet 2025, no 494749 (Lebon T.
Chilling injury to algal symbionts induces host starvation and metabolic reorganization in a temperate cnidarian
No full text● Global temperature anomalies increasingly disrupt the cnidarian-algal symbiosis through a phenomenon coined bleaching. In contrast to heat stress, the mechanisms underlying symbiotic breakdown under cold stress remain largely unknown. ● Combining physiological and metabolomic measurements, we investigated the response of the photosymbiotic sea anemone holobiont Aiptasia couchii to an experiment mimicking a cold spell in the Mediterranean Sea. ● Within four weeks, we observed the onset of symbiotic breakdown reflected in reduced algal endosymbiont density and chlorophyll a content. While photosynthetic efficiency remained largely unaffected, no gross photosynthesis was detectable in cold-stressed anemones and decreases in glycosyldiacylglycerols and fatty acyl glycosides indicated chloroplast lipid remobilization. This breakdown of symbiotic carbon cycling was reflected in increased dipeptide and ceramide levels suggesting anemones catabolized protein reserves and induced pre-apoptotic pathways. ● Taken together, these responses suggest a decoupling of light and dark reactions of photosynthesis in cold-stressed endosymbionts, resembling chilling injury in higher plants and free-living microalgae. This chilling-induced collapse of symbiotic nutrient cycling eventually leads to host starvation in cold-stressed Cnidaria. Hence, while cold and heat stress may invoke contrasting physiological effects on endosymbionts, our results suggest that both stressors destabilize the symbiosis through similar mechanisms rooted in host starvation
Embryonic Hormetic Priming Modulates Later‐Life Thermal Tolerance
No full textInternational audienceUnderstanding the mechanisms explaining thermal tolerance variation is crucial for predicting the impact of climate change on ectotherms, especially those living near their upper thermal limits. Among the various forms of plasticity, developmental plasticity holds promise as an adaptive trait for aquatic organisms to buffer the negative effects of ocean warming; however, its underlying molecular mechanisms remain poorly understood. Here, we examine the capacity of two bi-parental progenies of the black-lip pearl oyster, Pinctada margaritifera, to modify their later-life thermal tolerance and performance through developmental thermal priming. Embryos (3-24 h post-fertilization) were incubated until hatching at either control (28°C) or warm (32°C; ecological extremes) temperatures, and raised 4 months under common conditions at 28°C. Our results reveal family-specific effects of early-life thermal priming, significantly enhancing spat thermal tolerance in one family, while reducing it in the other. Main molecular pathways of heat stress response (at the sublethal temperature of 34°C) were conserved across families and independent of the early-life priming treatment. Nevertheless, a network-preservation approach allowed further characterizing the subtle, nested environmental "memory" mediated through network reorganization, particularly in gene regulatory pathways involved in the Unfolding Protein Response (UPR). While this 2 × 2 factorial design may capture an oversimplification of the complex relationship between early environments and later phenotypes, our study emphasizes the need to refine and develop new well-tuned experimental protocols to hold out the promise of hormetic priming for ecological conservation and aquaculture improvement
Coral degradation alters community diversity and stability of fish and invertebrate assemblages following recruitment
No full textInternational audienceHabitat degradation is one of the most pervasive threats to coral reef ecosystems, and the intensification of global and local disturbances is expected to further exacerbate its impacts. While many studies have investigated the effects of coral degradation on fish and invertebrates separately, its impact on the settlement and recruitment of entire coral-associated communities remains poorly understood. To fill this gap, we experimentally quantified how coral status (live versus dead) and ecological process (settlement: after 7 d, and recruitment: after 28-30 d) shape the abundance, diversity and community composition of coral-dwelling organisms in the back reef of Mo’orea, French Polynesia. Live corals supported significantly higher abundance, species richness and Shannon diversity at the recruitment stage, whereas no differences were detected during settlement. Similarly, recruits on live coral exhibited lower compositional variability, fostering a more ecologically stable community over time. Both coral status and ecological process significantly influenced taxonomic and feeding guilds, although their effects were independent. Overall, our findings demonstrate that live corals provide structurally complex, resource-rich habitats that enhance biodiversity and promote the establishment of more stable and functionally diverse communities. Coral degradation, in contrast, disrupts these dynamics, affecting not only fish communities but the entire benthic assemblage associated with corals, altering key ecological functions and potentially reducing reef resilience. Understanding how coral degradation affects settlement and recruitment across taxa is essential for preserving healthy coral structures, which should be prioritized to sustain the ecological integrity and trophic functioning of reef ecosystems
Using a comprehensive donor and host dataset to decipher the heritability and genetic architecture of pearl traits in the black-lipped oyster (Pinctada margaritifera)
No full textInternational audienc
A holistic approach to evaluating climate vulnerability of French Polynesia pearl oyster farming: Bridging communities and scientific knowledge
No full textInternational audienceWhile there is wide consensus about the reliance of climate projections at global scale, there is still uncertainty about changes at finer scale and even less on the effects of such fluctuation for local economies and societies. The vulnerability of social-ecological systems (SES) to climate change is a framework that takes into account the strong link between environment and local communities that depend on ecosystem services to ensure their livelihoods. This study explores the vulnerability of pearl farming SES to climate change, combining scientific insights with local knowledge from French Polynesian communities. A preliminary list of eighty-two criteria of exposure, sensitivity and adaptive capacity, identified through a targeted scoping review, was used to develop the interview guide that informed fifty-six face-to-face interviews and workshops conducted in 2020 and 2025. Using a combination of ranking questions and open-ended responses, the results highlight differences in the perceived exposure between scientific/institutional actors and local communities, which is reflected in the degree of sensitivity of the SES to climate drivers. Expectedly, the priorities given to adaptation measures were also different. The thematic analysis of the responses, however, shows that the two parties are aware of their own limitations in understanding the effects of climate change and recognise the need to fill mutual gaps through a collaborative production of knowledge. By integrating complementary forms of knowledge, this approach may help overcome the limitations of vulnerability assessments based exclusively on scientific expertise, and support the development of climate policies that are scientifically sound and socially accepted
