Biology subjects

Lutier, M.

Publications and source records attributed to Lutier, M..

6 recordsLinked to original sources

bioRxiv2026

Biochemical Indicators of Atlantification and Diapause Strategy in Arctic Copepods Point to a Decrease in Copepod-mediated Carbon Sequestration

Arctic ecosystems are critically endangered by rising temperatures and changing hydrography, especially the intrusion of increasingly warm water from the Atlantic Ocean known as Atlantification. In addition to housing fragile biodiversity, Arctic copepods and their lipids play a crucial role in cycling carbon by transporting carbon into the deep ocean through their diapausing behaviors. Here, we explored the lipidomes of the Arctic copepod Calanus glacialis, collected from three fjords around Svalbard during November 2022 when C. glacialis are known to be in diapause. These three field sites provide a natural laboratory experiment, as they are influenced by different water masses with varying degrees of Atlantic water, and experience vast differences in sea ice coverage over the year. These environmental differences were clearly reflected in the lipidomic analysis, with stations influenced most by Atlantic Warm Water having the lowest total lipid concentrations and the lowest accumulation of storage lipids necessary for entering diapause. Membrane lipids were a significant proportion of the Svalbard copepod lipidomes, with the highest ratios observed at the Atlantified site. The high membrane lipid and high triacylglycerol concentrations were interpreted as signs of active feeding. This was further corroborated by fatty acid composition analysis, which revealed dietary biomarkers of carnivory at Atlantified sites. The copepods from the site most insulated from Atlantic influence had more than double the amount of storage lipids per individual and fatty acids associated with diatom biomass, indicating assimilation in the spring. Ultimately, the decrease in lipid content observed in association with Atlantification around Svalbard will impact diapause patterns, as Calanus species need 20-30% more WE to successfully complete diapause. In turn, this will impact the magnitude of carbon sequestration through the seasonal lipid pump, not to mention having radiating effects through the Arctic food web where Calanus glacialis plays an important role. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=131 SRC="FIGDIR/small/738257v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@131e2org.highwire.dtl.DTLVardef@72071aorg.highwire.dtl.DTLVardef@3059f0org.highwire.dtl.DTLVardef@60a5ea_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2025

Stressed Overwintering Bottleneck Hypothesis: Ocean warming and acidification synergistically disrupt Arctic zooplankton overwintering

Ocean warming (OW), driven by the influx of warm Atlantic water masses, and acidification (OA) are threatening Arctic marine ecosystems. However, their potential synergistic effects are poorly understood, especially during the Polar Night when marine species are particularly vulnerable to stressors. Here, we tested our novel Stressed Overwintering Bottleneck Hypothesis (SOBH): warming will disrupt the overwintering of the keystone pan-Arctic copepod Calanus glacialis, a pivotal secondary producer, by impairing fitness-related traits underpinning survival and reproduction. We exposed C. glacialis to current and projected future OW levels (0 {degrees}C and 4 {degrees}C) and OA levels (pH 8.0 and 7.4-7.3) for 53 days during the mid-Arctic Polar Night. We assessed survival, development, and physiological and molecular mechanisms (oxygen consumption, lipid depletion, the expression of nine targeted genes related to oxidative stress and damage repair, and DNA damage). OW alone did not affect C. glacialis mortality; however, OA increased copepod survival at 0 {degrees}C. Notably, their combined effects (OWA) synergistically doubled mortality, as predicted by SOBH. Warming also accelerated moulting from copepodite stage V to adulthood in December, and increased respiration, exhausted lipid reserves entirely by early March, approximately one to four months before the spring algal bloom, further supporting SOBH. DNA damage and gene expression patterns indicated low investment in maintenance and damage repair. Collectively, these findings reveal hidden mechanisms by which OW and OA synergistically threaten overwintering Calanus copepods by drastically increasing mortality, accelerating moulting, raising metabolic rates, and causing early lipid depletion. These effects generate cross-seasonal phenological mismatches among overwintering survival, energy reserves, reproduction, and primary production. Such stressed overwintering bottlenecks in foundational secondary producers like Calanus copepods provide novel explanations for how OW and OA can constrict Arctic marine food webs. At a broader perspective, SOBH highlights how multiple stressors induced overwintering disruption could reshape pan-Arctic and global biodiversity.

ecology↗

bioRxiv2025

Sea surface freshening can suppress the thermal tipping point of marine copepods

Tipping points govern species distributions, which could be impacted by ocean warming (OW) and sea surface freshening (SSF). Interactions between these stressors may affect tipping points. Also, the accumulation of stress over time (degree day) could condition the reaching of tipping points. Yet, these aspects have never been studied. Here, we hypothesise that SSF reduces the thermal tipping point of Calanus spp., key copepods that play a structuring role in marine food webs. Calanus spp. from the Oslofjord were exposed to a temperature gradient from 8 to 20 {degrees}C and a salinity range from 35 to 10 PSU. We found that the survival of Calanus spp. tipped and decreased above temperatures of 14 - 18 {degrees}C, which are already reached in the surface waters of the Oslofjord during summer months. At 29 PSU, this corresponded to a tipping point of heat accumulation of 28 {degrees}C.d above which survival decreased. Reduced salinity below 29 PSU, prevalent year-round in surface waters, suppressed this tipping point, inducing linear decreases in survival when temperature rises above 8 {degrees}C. Thus, the thermal niche of Calanus spp. will decrease with SSF, impacting whole ecosystems. We provide the first statistical determination of heat accumulation tipping points. We also demonstrate that exposure to a secondary stressor can suppress tipping points to a primary stressor, thereby removing the ability of phenotypic plasticity to buffer negative impacts on fitness. This advances our knowledge of physiological tipping points, which are essential in a world where they are increasingly reached by environmental changes.

ecology↗

bioRxiv2025

The Arctic copepod Calanus hyperboreus is more tolerant to marine heatwaves than temperate copepods in the Oslofjord

Calanus hyperboreus plays a key role in the functioning of Arctic ecosystems. It is considered highly vulnerable to ocean warming (OW) and marine heatwaves (MHW), which would reduce its range, expected to shift northward. Yet, C. hyperboreus is reported as far south as the Skagerrak, where it is considered non-native and transported by ocean currents. We argue that this may be an isolated population adapted to warmer temperatures. To test this hypothesis, we exposed C. hyperboreus from the Oslofjord to temperatures from 0 to 24 {degrees}C, for 5 days. We recorded survival to identify the upper threshold of thermal tolerance and DNA damage to detect sublethal effects. The thermal response of C. hyperboreus was compared with that of the dominant copepod species in the Oslofjord, Calanus finmarchicus and Metridia longa. We found that the survival of C. hyperboreus did not decrease before reaching 16-20 {degrees}C which was much higher than 13-16 {degrees}C and 4-8 {degrees}C for C. finmarchicus and M. longa, respectively. C. hyperboreus showed the least DNA damage, highlighting the adaptation of its physiology to the Oslofjord. Our results suggest the existence of local adaptations to warming in C. hyperboreus that could determine its fate under climate change.

physiology↗

bioRxiv2023

Differential reaction norms to ocean acidification in two oyster species from contrasting habitats

Ocean acidification (OA), a consequence of the increase in anthropogenic emissions of carbon dioxide, causes major changes in the chemistry of carbonates in the ocean with deleterious effects on calcifying organisms. The pH/pCO2 range to which species are exposed in nature is important to consider when interpreting the response of coastal organisms to OA. In this context, emerging approaches, which assess the reaction norms of organisms to a wide pH gradient, are improving our understanding of tolerance thresholds and acclimation potential to OA. In this study, we decipher the reaction norms of two oyster species living in contrasting habitats: the intertidal oyster Crassostrea gigas and the subtidal flat oyster Ostrea edulis, which are two economically and ecologically valuable species in temperate ecosystems. Six-month-old oysters of each species were exposed in common garden for 48 days to a pH gradient ranging from 7.7 to 6.4 (total scale). Both species are tolerant down to a pH of 6.6 with high plasticity in fitness-related traits such as survival and growth. However, oysters undergo remodelling of membrane fatty acids to cope with decreasing pH along with shell bleaching impairing shell integrity and consequently animal fitness. Finally, our work reveals species-specific physiological responses and highlights that intertidal C. gigas seems to have a better acclimation potential to rapid and extreme OA changes than O. edulis. Overall, our study provides important data about the phenotypic plasticity and its limits in two oyster species, which is essential for assessing the challenges posed to marine organisms by OA.

physiology↗

bioRxiv2021

Revisiting tolerance to ocean acidification: insights from a new framework combining physiological and molecular tipping points of Pacific oyster

Studies on the impact of ocean acidification on marine organisms involve exposing organisms to future acidification scenarios as projected for open ocean, which has limited relevance for coastal calcifiers. Characterization of reaction norms across a range of pH and identification of tipping points beyond which detrimental effects are observed has been limited and focus on only a few macro-physiological traits. Here we filled this knowledge gap by developing a framework to analyze the broad macro-physiological and molecular responses over a wide pH range of juvenile Pacific oyster, a model species for which the tolerance threshold to acidification remains unknown. We identify low tipping points for physiological traits at pH 7.3-6.9 that coincide with a major reshuffling in membrane lipids and transcriptome. In contrast, shell parameters exhibit effects with pH drop well before tipping points, likely impacting animal fitness. These findings were made possible by the development of an innovative methodology to synthesize and identify the main patterns of variations in large -omic datasets, fit them to pH and identify molecular tipping-points. We propose the application of our framework broadly to the assessment of effects of global change on other organisms.

zoology↗