French Research Institute for Exploitation of the Sea
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How contrasted environments in the Humboldt Current System, Pacific Warm Pool and South Pacific Gyre, shape contrasted ecosystems. A modeling approach using APECOSM
No full textPelagic ecosystems exhibit a strong regional heterogeneity, driven by physical and biogeochemical characteristics. Using the global 3D marine ecosystem model APECOSM, we simulate six high-trophic-level communities, capturing their size structure, spatial distribution, and trophic interactions up to 1,000 meters depth. We examine how different environments shape their contrasting organisation and interactions in three Pacific Ocean regions: the productive Humboldt Current System, the oligotrophic South Pacific Gyre, and the thermally stratified Pacific Warm Pool.
Simulations reveal strong regional contrasts in ecosystem responses. In the Humboldt, high primary production supports important biomass of small coastal pelagic fish. Seasonal warming enables tuna to forage in these productive waters, while low-oxygen conditions restrict the vertical range and abundance of mesopelagic organisms and concentrate epipelagic organisms close to the surface. In the Warm Pool, apex predators remain abundant despite low primary production, thanks to efficient trophic transfer and biomass import from neighbouring regions. Seamounts concentrate mesopelagic organisms into shallow layers, making them accessible to epipelagic predators. In contrast, the South Pacific Gyre supports sparse, imported high-trophic-levels with limited trophic coupling and strong intra-community predation. We quantify regional differences in trophic transfer efficiency and network complexity, identifying thresholds below which high-trophic-levels collapse.
These findings illustrate the emergent plasticity of pelagic ecosystems and the importance of bottom-up control of high-trophic-level biomass. They emphasise the importance of temperature, transport, light and oxygen in modulating horizontal and vertical distributions, controlling the co-occurrence of predators and prey, and influencing the formation of schools, ultimately impacting trophic interactions and community assemblages
Extreme Mediterranean rainfall impact on sedimentary routing systems: what can we learn from Storm Alex using in situ detrital 10Be?
No full textUnderstanding how extreme meteorological events influence sediment transport is critical for predicting landscape evolution under a changing climate. Detrital cosmogenic 10Be can provide insights into sediment dynamics following extreme rainfall, but high-resolution datasets tracking 10Be variations before and after a storm, alongside long-term records, remain rare.
The Var catchment (French Southern Alps) presents a unique case study, as its 10Be signal was well-documented before the October 2020 Storm Alex (>500 mm of rainfall/24 h), which triggered flash floods, mobilized large sediment volumes, and formed a 10 km-long sediment plume in the Mediterranean Sea. We compare 10Be concentrations in river sediments collected pre-storm (2016–2018), and at +7 days, +21 days, +4 months, and +7 months post-storm. We also use a historical offshore sample and contextualize these results with a 75 ka-long 10Be record from deep-sea sediment cores.
At the Var outlet, 10Be concentrations initially increased by ~25 % at +7 and +21 days, attributed to the mobilization of 10Be-rich sediments from the upstream Var and Tinée sub-catchments. Concentrations returned to pre-storm levels within four months, primarily due to dilution with 10Be-poor sediments from the Vésubie sub-catchment fluvioglacial terraces. While short-term 10Be fluctuations at the Var outlet reflect complex sediment sourcing, our comparison with the 0–75 ka record confirms that major glaciation events and potential anthropic influences remain distinguishable, demonstrating that 10Be is a robust proxy of denudation changes, even when extreme events are involved
Three-dimensional management needs of deep-sea hydrothermal vent ecosystems
No full textDeep-sea hydrothermal vents form small, unique, and fragile ecosystems that are widely recognized as sites in need of protection. Deep-seabed mining (DSM) is a future threat to hydrothermal ecosystem integrity. In most areas within, and in all areas beyond national jurisdiction, currently proposed protection measures from DSM are unlikely to be sufficient, as only the known active venting sites on the seafloor are intended to be protected from DSM impacts. To ensure effective protection, we propose protecting not only the active vent sites but the entire hydrothermal ecosystems and their transition zones, embracing the seafloor, subseafloor and overlying water column. We discuss how ecological knowledge supports the proposed three-dimensional (3-D) protection. We suggest no DSM extraction or indirect impacts on the seafloor and entire subseafloor within a minimum 50 km diameter (25 km radius) around visible active vents. This will ensure the maintenance of subseafloor connections that are key for ecosystem integrity, as changes in vent fluid conditions can alter all ecosystem functions and services linked to venting activity. In the water column, protection from pollution from the seafloor to surface is suggested to protect vent larvae. This extent spans the entire length of ridges or back-arc basins, with a cross-axial extent of 80 km. We further discuss how international law can contribute to the effective protection of vent ecosystems and transition zones in international waters, and provide guidance for coastal States to safeguard these ecosystems and transition zones within their own maritime areas
Seeing yew for the forest: a call to action for improving conservation and restoration of the European yew (Taxus baccata L.)
No full textThe European yew (Taxus baccata L.) is a long-lived conifer of ecological, cultural, and historical importance across Eurasia. Despite its remarkable resilience, wide distribution, and symbolic importance, the species has experienced a long-term decline due to a complex interplay of climatic fluctuations, megafaunal extinctions, human exploitation, and insufficient regeneration. Recent studies in palaeoecology, archaeology, dendroecology, and conservation have revealed a species with greater ecological plasticity and a broader historical distribution than previously assumed. However, many fundamental questions remain unresolved, particularly regarding its biogeographical history, population dynamics, recruitment processes, and the drivers of its decline.
This review stems from prior investigations of yew in the French Pyrenees and, more broadly, across Europe. These efforts led to a transdisciplinary seminar and opened a collaboration uniting more than 30 researchers across Eurasia. By synthesizing a wide array of data and perspectives, the article highlights key knowledge gaps and outlines emerging research priorities. These are organized thematically—past, present, and future—and include 25 questions on the species' ecological niche, life-history strategies, human interactions, genetic resilience, and conservation under global change. The article advocates for a shift towards integrative and long-term conservation strategies that embrace the historical legacies of yew populations, the general ecology of the species along with local ecological context dependence, and the urgency of future threats. By identifying pressing research needs, this review seeks to lay the foundation for new collaborative initiatives and to support evidence-based conservation of this emblematic yet understudied species
Domoic acid production by a Pseudo-nitzschia australis strain under zinc and copper exposure
No full textThe diatom species Pseudo-nitzschia australis can produce domoic acid (DA), a neurotoxin- responsible for amnesic shellfish poisoning. Copper (Cu) and zinc (Zn) are essential trace metals for marine phytoplankton, but they can become either limiting or toxic at pico- to subnanomolar ionic concentrations—levels that are can be reached in coastal ecosystems. The effect of exposure to these metals on DA production remains unclear for Cu and is largely unknown for Zn. In this study, we investigated the effects of toxic picomolar concentrations of Cu²⁺ and four non-limiting concentrations of Zn²⁺ on the metabolism and physiology of a toxic P. australis strain isolated from the coastal waters of North Biscay (France). Using principal component analysis, we observed changes in cell populations over time depending on metal exposure. Cu²⁺ toxicity was marked by a 35% decrease in maximum cell density and a reduction in growth rate (µ₊Cu = 0.55 µₐₓ). DA production was differentially modulated by the two metals: toxic Cu²⁺ levels stimulated DA synthesis (+200%), while elevated Zn²⁺ bioavailability significantly decreased it (by up to –85%), including when Zn²⁺ was combined with toxic levels of Cu²⁺ (–65%). We further discuss DA production by P. australis as a potential protective mechanism against oxidative stress. Additional data on intracellular glutathione (GSH) quotas—an important reactive oxygen species (ROS) scavenger and Cu²⁺ chelator— are presented and linked to Zn2+ bioavailability. GSH cell quotas were significantly correlated with DA production (p < 0.05) further supporting existing links between metal exposition, oxydative stress and DA production. This study suggests that ambient concentrations of Cu²⁺ and Zn²⁺ are critical factors regulating DA production in coastal marine systems
Pollen transport to deep-marine environments: Considerations for reconstructing past vegetation from marine sediment cores
No full textDeep-marine sedimentary records provide a unique opportunity to investigate long-term vegetation changes in response to climate through pollen analysis. In contrast to pollen records from terrestrial sites which capture a local vegetation signature, deep-marine records typically capture a regional vegetation signature, with pollen often taking long and complex transport pathways before depositing on the seafloor. To use deep-marine pollen records to their full potential, we need to understand how pollen is reaching deep-marine sites and whether different transport processes (i.e. ocean currents or gravity flows) impact or bias the final palaeovegetation record. We compare three deep-marine pollen records from offshore eastern Aotearoa-New Zealand from different depths, proximities from land and sedimentary settings to understand whether these different factors influence the final palaeovegetation records. We focus on the glacial-interglacial transitions from Marine Isotope Stages 6-5 and 2-1, and present a new 135 ka pollen record from the turbidite-dominated sediment core IODP-U1520D. We find that pollen assemblages in the three cores show consistent changes over glacial-interglacial cycles, with pollen assemblages showing greater similarities in interglacial periods and varying during glacial periods. The general consistency in pollen assemblages is surprising given the vastly different nature of the three sediment cores and shows that deep-marine records, including fine-grained turbidite-dominated records from active margins, can yield reliable palaeovegetation records
A 1000-year-long record of diatom production and climate variability from the Gulf of Tehuantepec (Eastern Tropical North Pacific)
No full textWe examined the productivity variability in diatom assemblages during two contrasting climatological periods: the Medieval Warm Period (MWP) and the Little Ice Age (LIA), in the Gulf of Tehuantepec (GT), Eastern Tropical North Pacific. The GT is an important fisheries region in Southern Mexico, largely dependent on ocean productivity. Climatologically, the GT is seasonally affected by a strong north-wind regime and the Intertropical Convergence Zone interactions. These winds promote intense mixing and upwelling in winter to spring months and stratification conditions during the rest of the year; therefore, this climatic variability is expected to have been affected by the MWP and LIA conditions. The MWP (~784 to ~1426 CE) was characterized by the predominance of a warm-water and low-productivity assemblage formed by Neodelphineis pelagica, Thalassionema nitzschioides var. parvum, Thalassiosira eccentrica, Thalassiosira oestrupii, Cyclotella litoralis, Thalassiosira lineata, Fragilariopsis doliolus, Nitzschia interruptestriata and other minor taxa. Early LIA (~1436 to ~1620 CE) was characterized by the predominance of a cold-water and high-productivity diatom assemblage constituted by Chaetoceros spores, Thalassionema nitzschioides, Thalassionema bacillare, Lioloma pacificum, and Thalassiosira nanolineata. Comparing the MWP diatom assemblage to that from the Current Warm Period (1850 CE to present, as reported in a previously published study in the GT) showed that the last 150 years have been the warmest in the integrated ~1400-year GT record
Plastic Pollution in Leeward, Moorea and Cook Islands (South Pacific): A Baseline Study
No full textPlastic pollution is increasingly affecting the South Pacific, including remote islands and coastal regions of Small Island Developing States (SIDS), yet data remain sparse in many areas. This baseline study presents original data on beach macrolitter and microplastics in surface waters and sediments across six islands of French Polynesia (Moorea, Bora Bora, Tahaa) and the Cook Islands (Aitutaki, Rarotonga), collected during an opportunistic cruise in 2024.Beach surveys revealed high plastic contamination on most sites, with macroplastics (size > 2.5 cm) densities ranging from 18 to 58 items/100 m, exceeding European threshold values (e.g. 22 items/100m) on majority of sampled beaches. Single-use plastics and plastic fragments dominated the debris, with local sources such as tourism and coastal activities clearly identifiable.Surface microplastics (315 µm–5 mm) were found at low densities, ranging from 0 to 4668 particles/km2, confirming relatively low contamination in surface waters. Only 17 particles were detected from 8 manta net tows. Sediment and beach microplastic analysis yielded very limited results, with microplastics found at only two sites (Huahine and Rarotonga), dominated by fragments and colored fibers. These results suggest localized contamination linked to urbanization and tourism rather than widespread oceanic inputs.Despite methodological limitations due to the cruise format, this study contributes rare data from under-sampled regions, supporting long-term monitoring efforts and informing future policy and mitigation actions. The results underline the need to improve regional waste management, which will be beneficial for local societies largely based on tourism
Exploring the environmental distribution of the oyster parasite Haplosporidium costale
No full textThe protozoan parasite Haplosporidium costale is known to occur in the USA where it has been associated with sharp seasonal mortality of the Eastern oyster Crassostrea virginica since the 1960’s. In 2019, the parasite was detected for the first time in the Pacific oyster Magallana gigas in France in the context of light mortality and was subsequently detected in archived material collected since 2008. This detection raised several questions regarding the ability of the parasite to maintain in the ecosystem and the potential involvement of other species in its life cycle. To answer these questions, an integrated sampling approach was deployed seasonally in three oyster farming areas where the parasite was already known to occur. Parasite presence was evaluated after checking the presence of PCR inhibitors and using a previously developed and validated Real Time PCR assay, optimized in this study to detect parasite DNA in various environmental compartments. Parasite DNA was almost only detected in cupped oysters. Considering the high number of oysters found positive with low infection intensity, a complementary experiment was undertaken to better characterize sub-clinical infections in oysters. The presence of the parasite was tested twice a week in water and sediment from aquaria hosting cupped oysters from a known infected site. After one month, oysters were sacrificed and tested regarding the presence of the parasite at the tissular level. Altogether, field and experimental results indicate that the parasite is stably established in oyster, particularly in gills, which may act as a reservoir all along the year. The detection of parasite DNA in nanoplankton and sediment suggests that H. costale is released from the oysters outside mortality event. Our results do not support the involvement of other species than cupped oyster in the parasite life cycle except periwinkles, whose role would deserve to be further investigate
Relationship between REE signatures and biological traits of marine benthic fauna in a temperate mud patch: Application of multivariate analyses
No full textThe increasing contamination of coastal environments by Rare Earth Elements (REEs) necessitates a thorough understanding of the dynamics of these elements in ecosystems under anthropogenic pressure. Sedimentary bodies influenced by large rivers, such as the West Gironde Mud Patch (WGMP), are among these pressured ecosystems. REE analyses in seven benthic marine species and ambient media (i.e., dissolved fraction of bottom water, sediments) of this mud patch has provided REE signatures (i.e., REE concentrations and shape of normalized patterns) using one concentration descriptor (i.e., ∑REE) and six descriptors of pattern shapes (i.e., La/La*; Ce/Ce*; Eu/Eu*; Pr/Lu; Pr/Gd; Gd/Lu). A robust procedure of multivariate analyses (i.e., PERMDISP, PERMANOVAs, PCO) was applied to study the controlling factors of REE signatures in these species.
Assessment of the within- and between-species variability suggests that differences in REE concentrations and shapes of normalized patterns between species were related to the ambient media's geochemical processes and the fauna's ecological and biological traits. REE concentrations in the fauna document trophic dilution, reflected by elevated concentrations in pure microphages and reduced concentrations in pure carnivores. The predominance of calcareous skeletons in bivalves and brittle stars results in a dilution effect on REE concentrations at the whole-organism level. The chitinous exoskeleton of crabs and shrimps is subject to adsorption processes for REEs present in the sediment