French Research Institute for Exploitation of the Sea
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Multiscale Physiological Responses to Organic and Inorganic Pollution in the Invasive Mosquitofish Gambusia Holbrooki
No full textAnthropic activities often lead to the contamination of freshwater ecosystems by organic and inorganic pollutants with potential deleterious effects on wildlife health. However, some species such as the invasive mosquitofish (Gambusia holbrooki) can thrive in such polluted habitats, but the underpinning mechanisms are still unknown. The aim of this study was to characterize the physiological response of mosquitofish living along different pollution gradients in South of France. Eleven sites were selected according to various levels of pollutants in the water (pesticides, pharmaceuticals) and in mosquitofish tissue (PAHs, PBDEs, PCBs, organochlorines, metals). The level of the different pollutants varied among sites resulting in contrasted pollution gradients. The biological response of mosquitofish was measured using biomarkers of biotransformation, oxidative status, neurotoxicity and histopathological alteration in gills and liver. Muscle lipids, hepatosomatic condition, body condition and reproductive status were also measured. We used a Structural Equation Modelling (SEM) approach to characterize the direct and indirect effects of pollutants across biological levels. Results showed that high levels of POPs and metals affected biotransformation processes in both sexes, as well as non-enzymatic antioxidants level and resulted in gill histopathological alterations in females. In addition, pesticides increased the energetic demand reflected by reduced lipid storage in females and hepatosomatic condition in males. Interestingly, responses to pollution varied among sexes since females responded to a broader range of pollutant types than males. This study highlights some key traits underlying the tolerance to pollution of the mosquitofish, which could partly explain their invasive success in polluted ecosystems
Life after death: Hidden diversity of orchids across European cemeteries
No full textHabitats sensitive to anthropogenic pressures are growing in conservation importance in the protection and perpetuation of rare animal and plant species. Although natural habitats sensitive to disturbance in urban areas have mostly declined in availability, patches offer conservation opportunities for wildlife that are fundamental to maintaining biodiversity. Human burial sites can contribute to this: they are more numerous and greater in extent in more urbanized areas, but their significance in the maintenance and promotion of biodiversity has not been considered across Europe and other continents. Because of their high sensitivity to even minor disturbance to natural habitats, orchid diversity is a key bioindicator of terrestrial ecosystem function. We evaluated orchid diversity in cemeteries of 13 European countries. Comprehensive field surveys of orchid flora in 2079 locations revealed that they occurred in every country visited and in high variability in both the number of taxa (n = 65) and individual plant counts (n = 44680). We propose that cemeteries are of major importance as refugia in conserving orchids in most of the visited European countries; however, one of the most urgent issues is to identify the many anthropogenic factors determining biodiversity of cemeteries, and to eliminate some newly emerged management practices in cemeteries that undermine biodiversity, including the orchid flora. Human burial grounds are therefore not just important in preserving the history of humankind; they are key in protecting biodiversity in this modern era of unprecedented anthropogenic changes to our terrestrial environments, especially as a result of rapid and unrelenting urbanization
Multi‐annual variability of storm events and morphological response in the SW Iceland: The Valahnúkamöl boulder barrier
No full textWhile many studies have highlighted the high mobility of gravel/pebble beaches due to storm waves, further research is needed to improve understanding of the morphodynamic of coastal boulder accumulations. This paper provides original data about storm‐induced morphogenetic processes for the Valahnúkamöl boulder barrier located in the Reykjanes Peninsula (SW Iceland). The study is based on annual topo‐morphological surveys conducted from 2015 to 2023 and a shoreline change analysis for the period 1978–2023 using a series of aerial photos. In addition, hydrodynamic conditions (wave and water levels) were analysed using field records and model results. Results show a good correspondence of the morphological changes of the barrier to the frequency/energy of morphogenetic events. Interannual surveys (2015–2023) indicate a high mobility of boulders across the beachface regardless of the variability of hydrodynamic conditions. In contrast, boulders located on the crest and the back‐barrier moved more episodically by overtopping and overwashing processes during extreme events combining storm waves and high spring tide levels. A massive landward transfer of boulders resulting in the most significant barrier retreat, −6.1 m, was recorded during the winter 2022. Between 1978 and 2023, the mesoscale shoreline changes of the barrier retreated landward by rollover. The pluri‐decadal variability in shoreline retreat rates seemed to be strongly controlled by extreme hydrodynamic conditions. However, this cross‐shore dynamic responses to episodic overwash depended on specific geological constraints. This survey provides a first quantitative assessment of the morphological impact of significant morphogenetic events within the highly energetic hydrodynamic context of SW Iceland. These data complement surveys undergone through a wide range of coastal morphologies elsewhere along the Western coasts of the North Atlantic basin. Such assessments may prove useful in anticipating the potential intensification of hydrodynamic conditions at mid‐latitudes due to climate change
Argo Quality Control Manual for CTD and Trajectory Data
No full textA CTD (conductivity, temperature, depth) device measures temperature and salinity versus pressure. This document is the Argo quality control manual for CTD and trajectory data. It describes two levels of quality control:
- The first level is the real-time system that performs a set of agreed automatic checks.
- The second level of quality control is the delayed-mode system.
These quality control procedures are applied to the parameters JULD, LATITUDE, LONGITUDE, PRES, TEMP, PSAL, and CNDC
To Drug or not to Drug? Impacts of the aquaculture antibiotic Florfenicol on Marine Plankton
No full textHighlights• First mesocosm experiment addressing the effects of Florfenicol on the plankton food web• A five-day, real-life dosage scenario of the commercial AQUAFLOR MSD Type A article• Trophic interactions among plankton communities (from bacteria to copepods) were studied• Significant impacts on cell abundances and process rates in the microbial food web were observed• Prolonged exposure to FFC triggered a rise in FFC-resistant bacteria and caused toxic effects mainly on phytoplankto
High-frequency monitoring reveals recurrent extreme events in a tropical estuary
No full textEstuaries of the tropical Guiana Shield exhibit rapid short-term variability superimposed on strong seasonal forcing, yet high-frequency, multi-year observations remain scarce. A four-year record (Jan 2020–Mar 2024; 20-min resolution) of temperature, salinity, and dissolved oxygen from four sites along the Cayenne River estuary was assembled to assess cross-site coherence, diel ranges, temporal signals, and extreme events (hyposalinity, hypoxia and thermal anomalies). Temperature and salinity showed strong coherence among sites and clear seasonal cycles, with higher values in the dry season and pronounced freshening in the wet season. Oxygen was more heterogeneous, reflecting local biophysical controls. Extreme-event analysis revealed frequent hyposalinity and hypoxia, whereas thermal anomalies were less common and typically shorter. A predictive model driven by atmospheric temperature and river discharge was able to estimate daily water temperature and salinity variability, while skill for oxygen was weaker, indicating the need to include additional biogeochemical drivers. This study establishes a high-frequency baseline for a data-poor tropical estuary, demonstrate that hydrological and atmospheric variability dominate the physical template, and show both the utility and limits of statistical prediction for anticipating biologically relevant extremes. Sustained high-resolution monitoring, paired with expanded biogeochemical measurements, will improve detection of climate-sensitive events and support adaptive management of estuarine nursery habitats and fisheries resources across tropical systems
Physiological and metabolic response of the bloody cockle (Senilia senilis) to salinity in the Sine Saloum estuary, Senegal
No full textEstuaries are unique ecosystems that experience dynamic environmental conditions. Organisms in estuaries face significant and rapid fluctuations in salinity caused by tidal variations, evaporation, rainfall, and freshwater runoff. This is especially true for bivalve mollusks, which cannot move to escape unfavorable conditions. Consequently, variations in salinity can significantly influence their life-history traits. Here, we examined the response of the bloody cockle, Senilia senilis, to variations in salinity. This bivalve is predominant in the estuaries of West Africa and supports a significant artisanal fishing activity. Experiments were conducted in an in situ laboratory to assess the behavioural (valve opening/closing), physiological (respiration, filtration) and osmoregulatory responses of the species to changes in salinity. The results help us define the species' tolerance and functional niche ranges:: (1) closing behavior occurs at salinities above 12 and 60, (2) filtration stops at salinities above 25 and 40, and (3) respiration increases on either side of an optimal salinity of 40. Analysis of internal osmolarity confirms that S. senilis is an osmoconformer, as its osmolarity strongly correlates with that of seawater. These responses underline the adaptation of this species to an estuarine habitat subject to intense salinity fluctuations, while identifying tolerance thresholds beyond which its vital functions are impaired. These results are crucial for understanding the resilience of S. senilis in the context of global change and for anticipating the effects of increased estuarine salinity on benthic biodiversity and associated ecosystem services
Vulnerability of marine megafauna to global at‐sea anthropogenic threats
No full textMarine megafauna species are affected by a wide range of anthropogenic threats. To evaluate the risk of such threats, species’ vulnerability to each threat must first be determined. We build on the existing threats classification scheme and ranking system of the International Union for Conservation of Nature (IUCN) Red List of Threatened Species by assessing the vulnerability of 256 marine megafauna species to 23 at‐sea threats. The threats we considered included individual fishing gear types, climate‐change‐related subthreats not previously assessed, and threats associated with coastal impacts and maritime disturbances. Our ratings resulted in 70 species having high vulnerability ( v > 0.778 out of 1) to at least 1 threat, primarily drifting longlines, temperature extremes, or fixed gear. These 3 threats were also considered to have the most severe effects (i.e., steepest population declines). Overall, temperature extremes and plastics and other solid waste were rated as affecting the largest proportion of populations. Penguins, pinnipeds, and polar bears had the highest vulnerability to temperature extremes. Bony fishes had the highest vulnerability to drifting longlines and plastics and other solid waste; pelagic cetaceans to 4 maritime disturbance threats; elasmobranchs to 5 fishing threats; and flying birds to drifting longlines and 2 maritime disturbance threats. Sirenians and turtles had the highest vulnerability to at least one threat from all 4 categories. Despite not necessarily having severe effects for most taxonomic groups, temperature extremes were rated among the top threats for all taxa except bony fishes. The vulnerability scores we provide are an important first step in estimating the risk of threats to marine megafauna. Importantly, they help differentiate scope from severity, which is key to identifying threats that should be prioritized for mitigation
Effects of a simulated marine heatwave on the structure and composition of Mediterranean plankton in a mesocosm study
No full textCoastal marine systems are particularly affected by marine heatwaves (MHW), which affect organisms, including plankton communities, that are essential for ecosystem function and productivity. To study their effects on plankton food web components, an in situ mesocosm experiment was conducted in Thau Lagoon (Mediterranean Sea, South France) from May to June 2019. The two conditions were applied in triplicate. A MHW of + 3 °C above the natural lagoon water temperature was applied to three mesocosms and maintained for the first 10 days of the experiment. Afterward heating was discontinued, and temperatures returned to ambient levels for the remaining 10 days. The other three mesocosms were maintained at natural water temperatures throughout the experiment. Phytoplankton responded positively to MHW, whereas protozooplankton and viruses exhibited significant negative responses. The decrease in protozooplankton, which predominantly preyed on phytoplankton, can be explained by the increase in metazooplankton observed under MHW. Increased predation by metazooplankton on protozooplankton reduced their grazing pressure on phytoplankton, allowing them to proliferate. Simultaneously, metazooplankton directly grazed on larger phytoplankton cells, thereby reinforcing the shift in community composition towards smaller species following the simulated MHW. These combined top-down effects led to pronounced changes in both the structure and size of phytoplankton communities under MHW condition, driven by trophic cascades within the planktonic food web. Plankton functional group stability metrics showed that smaller communities were more resistant to MHW than larger communities. Nanophytoplankton, autotrophic flagellates, heterotrophic dinoflagellates, and tintinnids exhibited minimal recovery, whereas other plankton communities displayed a pronounced capacity for full or near-complete recovery following MHW. The contrasting resistance, resilience, and recovery of planktonic functional groups to MHW led to a restructuring of the planktonic food web and its function, with potential consequences for key ecological processes in the pelagic ecosystem
Long term decline of the planktonic biomass in a hotspot of nitrogen fixation
No full textOceanic N2 fixation by diazotrophic microorganisms is the primary external source of new nitrogen to the surface ocean sustaining net production of organic matter. Studying long-term trends in biomass within N2 fixation hotspots is crucial for understanding and predicting the response of N2 fixation to global climate change. Here we developed a bio-optical model based on the spectral phytoplankton absorption coefficient derived from satellite ocean color observations to estimate a proxy for particulate organic nitrogen in the western tropical South Pacific. We demonstrate the existence of a seasonal new biomass production annually over the past 20 years, likely driven by recurrent N2 fixation. Importantly, our results also reveal a gradual decline in biomass within this N2 fixation hotspot over the last two decades. This decline indicates that seasonal nitrogen inputs via N2 fixation are decreasing. This trend inevitably could lead to a decline in the efficiency of the biological carbon pump, with potential implications for global biogeochemical cycles and climate regulation