French Research Institute for Exploitation of the Sea
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Holocene paleoenvironmental reconstructions in western Brittany Bay of Brest: Part I – Understanding the spatial distribution of palynological records
No full textThe Bay of Brest (BB) is a shallow estuarine environment in NW France. This semi-enclosed basin of 180 km² is subject to multiple hydrodynamic factors including the dual influence of oceanic currents and fluvial discharges (Aulne and Elorn main rivers) and resulting in complex hydro-climatic and hydro-sedimentary processes. This study investigates with palynological data (continental: pollen grains and marine: dinoflagellate cysts) two kinds of different materials: (i) modern surface sediments collected over the whole BB as well as (ii) three new BB sediment cores (core ‘F’ from the mouth of the Aulne river and cores PALM-KS05 and PALM-KS06 from the Brest harbour). While modern data are analysed from a statistical point of view to highlight the influence of hydrodynamic forcing on the modern distribution of palynomorphs, the cores allow for spatial comparisons of palynological data on three windows over the Early (~9.5 and ~8.5 ka BP), Middle (~4.4–4.3 ka BP interval) and Late (~1–0.9 ka BP interval) Holocene. For each time intervals, two cores located along a transect from west (more pronounced oceanic influence) to east (more intense fluvial influence from the Aulne river) are compared, located on either side of a limit that we referred to as the river-induced palynological signal (RIPS) limit. These different comparisons reveal a high degree of spatial homogeneity in BB pollen records over time, with exceptions for environments east of the RIPS limit, for which rainfall-induced fluvial discharges have a stronger impact especially considering riparian taxa (i.e. Alnus). This is intended to improve understanding of the palynological signals recorded at different BB coring sites, a first step of crucial relevance before the establishment of a palynological stack covering the Holocene from several cores collected in different shallow bays of the BB (see Valero et al., submitted – PART II)
Effects of protection on large‐bodied reef fishes in the western Indian Ocean
No full textPredatory and large‐bodied coral reef fishes have fundamental roles in the functioning and biodiversity of coral reef ecosystems, but their populations are declining, largely due to overexploitation in fisheries. These fishes include sharks, groupers, Humphead wrasse (Cheilinus undulatus), and Green Humphead parrotfish (Bolbometopon muricatum). In the western Indian Ocean, this situation is exacerbated by limited population data on these fishes, including from conventional visual census methods, which limit the surface area surveyed. We developed a rapid timed scuba swim survey approach for application over large areas for estimation of the abundance of large‐bodied reef fishes and assessment of the effectiveness of marine protected areas (MPAs) in maintaining these species’ populations. Using this method, we sampled 7 regions in the western central Indian Ocean and Gulf of Aden, including 2 remote reference locations where fishing is prohibited. Eight families were selected for the surveys from across 3 categories: pelagic, demersal, and large‐bodied single species. Sharks (Carcharhinidae) were absent in 5 of the 7 regions, observed only in Mozambique and the Chagos Archipelago. Tunas (Scombridae) and barracudas (Sphyraenidae) were rarely observed (none in Madagascar, Djibouti, and Iles Glorieuses). The Giant grouper (Epinephelus lanceolatus) was absent in all regions, Humphead wrasse was absent in Comoros and Iles Glorieuses, and Green Humphead parrotfish was observed at only one site in Tanzania. The MPAs were not effective in protecting these single large‐bodied species or the 4 pelagic families, except for sharks in the highly protected reference locations. However, MPAs with medium levels of protection were effective in maintaining the abundance of some demersal families, notably large‐bodied groupers. Our results support the hypothesis of local extirpation of these large‐bodied fishes on many coral reefs in the western Indian Ocean
Footwall Geology and Deformation at Flip‐Flop Mid‐Ocean Ridge Detachment Faults: 64°35′E Southwest Indian Ridge (SWIR)
No full textUsing bathymetry and ROV dives, we investigate two successive flip‐flop detachment faults (D1 active, D2 older) in the near‐amagmatic 64°35′E region of the SWIR. Kilometer‐sized benches on the upper slopes of D1 footwall form the D1 degraded breakaway. Scarps at the top expose the D2 fault zone with deformed serpentinized peridotite, sigmoidal phacoids, planar fractures, and serpentinite microbreccia/gouge horizons. Two ROV sections of the D1 footwall show contrasting deformation styles, corresponding to distinct morphological domains, which relate to contrasting fault and footwall strength. One section documents corrugations, outcrops dominated by sigmoidal phacoids, and planar fractures with thin, discontinuous serpentinite microbreccia/gouge horizons. ROV dives in this corrugated domain show that NNE‐trending km‐spaced ridges and WNW‐trending narrow benches in the shipboard bathymetry correspond, respectively, to broad undulations (mega‐corrugations) of the D1 fault and to several antithetic minor normal faults (cumulated horizontal offset of ∼285 m). The other section, lacking corrugations, broad ridges, and antithetic fault, has thicker and more continuous serpentinite microbreccia/gouge horizons, indicating a weaker fault. The abundance of such weak gouges probably reflects hydrous fluid availability during deformation. We link mega‐corrugations in the western domain and km‐scale lobes of D1 emergence to a broad detachment damage zone with up to ∼600 m‐thick mega‐phacoids of less deformed serpentinized peridotite. Small antithetic normal faults in the corrugated domain are interpreted as due to bending forces in the D1 footwall. Our findings highlight the three‐dimensional, non‐planar structural and morphological variability of the exhumed D1 detachment fault zone along the ridge‐axis
Ecosystem changes after Early Cretaceous seawater intrusion into the proto-South Atlantic Ocean
No full textThe early evolution of the South Atlantic Ocean following the Cretaceous break-up of Gondwana is extensively recorded in rift basins along the conjugate margins of Africa and Brazil. For the Brazil side, divergent views of the source and pathway of the initial seawater incursion persist due to a paucity of recognized transitional sequences that document marine transgressive deposits over the continental interior. To address this, we conducted a high-resolution sedimentological and geochemical study through a core in the Campos Basin that encompasses the key lithologic switch from lacustrine carbonate to marine evaporite settings. Steroid lipid biomarkers, derived from pelagophyte marine algae, make a striking appearance in concert with a pronounced negative shift of 87Sr/86Sr ratios and coincident with the appearance of anhydrite. Importantly, the sulfur-sequestered biomarkers reveal a dynamic system where redox-stratified and anoxic conditions were amplified along with a deepening chemocline through the marine transition
Automatic detection, identification and counting of deep-water snappers on underwater baited video using deep learning
No full textDeep-sea demersal fisheries in the Pacific have strong commercial, cultural, and recreational value, especially snappers (Lutjanidae) which make the bulk of catches. Yet, managing these fisheries is challenging due to the scarcity of data. Stereo-Baited Remote Underwater Video Stations (BRUVS) can provide valuable quantitative information on fish stocks, but manually processing large amounts of videos is time-consuming and sometimes unrealistic. To address this issue, we used a Region-based Convolutional Neural Network (Faster R-CNN), a deep learning architecture to automatically detect, identify and count deep-water snappers in BRUVS. Videos were collected in New Caledonia (South Pacific) at depths ranging from 47 to 552 m. Using a dataset of 12,100 annotations from 11 deep-water snapper species observed in 6,364 images, we obtained good model performance for the 6 species with sufficient annotations (F-measures >0.7, up to 0.87). The correlation between automatic and manual estimates of fish MaxN abundance in videos was high (0.72 – 0.9), but the Faster R-CNN showed an underestimation bias at higher abundances. A semi-automatic protocol where our model supported manual observers in processing BRUVS footage improved performance with a correlation of 0.96 with manual counts and a perfect match (R=1) for some key species. This model can already assist manual observers to semi-automatically process BRUVS footage and will certainly improve when more training data will be available to decrease the rate of false negatives. This study further shows that the use of artificial intelligence in marine science is progressive but warranted for the future
Pollution by polar pesticides and pharmaceuticals and risk assessment in surface water bodies along the French Mediterranean coast: Complementarity of target and non-target screenings
No full textAnthropogenic activities are the source of a wide range of organic micropollutants (OMPs) found in all water bodies. Among them, pharmaceuticals and pesticides are the most found in watercourses and their impacts on non-target organisms have already been documented. Pesticides are well monitored in the river-lagoon continuum with their integration into the European water frame directory (WFD). However, their presence may co-occur with pharmaceuticals from wastewater treatment plants discharges in watersheds. Their monitoring and risk assessment is an important knowledge gap in the WFD strategy. In this study, we used polar organic chemical integrative samplers to assess the concentrations of pharmaceuticals and pesticides (parent compounds and transformation products) in water bodies of the French Mediterranean coast and to assess environmental risk during late spring-early summer. Internal concentration of pharmaceuticals in mosquitofish was assessed to evaluate fish pharmaceutical burden. A non-target screening method was used to complementary describe OMPs cocktail in water. Twenty-nine pharmaceuticals and 12 pesticides were quantified using a targeted approach and a further 6 pesticides and 22 pharmaceuticals using a non-target screening. Pharmaceuticals concentration and associated environmental risk were higher than pesticides ones in mixed-used watersheds, although their risk assessment was limited by the low number of ecotoxicological data available for pharmaceuticals. Four pharmaceuticals were found in fish tissue, increasing potential biological impacts for this trophic level. This study highlights the importance of monitoring concentrations of pharmaceutical products in the environment and increasing the ecotoxicological testing effort to improve risk assessment
Working Group on Ecological Carrying Capacity in Aquaculture(WGECCA; Outputs from 2024 Meeting)
No full textHydrographic section along 55° E in the Indian and Southern oceans
No full textA hydrographic section along 55° E, south of 30° S, was visited from December 2019 to January 2020 as the first occupation under the Global Ocean Ship-based Hydrographic Investigations Program. The water column was measured from the sea surface to 10 dbar above the bottom with eddy-resolving station spacings and state-of-the-art accuracy. The upper profile was characterised by a conspicuous front between 42.5 and 43° S and a cold-core eddy at 39° S. The front was identified as the confluence of Subtropical and Subantarctic fronts. The Agulhas Return Current front was found at 41.6° S. When combined with the section north of 30° S observed in 2018, another subsurface front was found in dissolved oxygen around 28° S at depths of 1500 to 3000 dbar. In the eastern Weddell–Enderby Abyssal Plain, no obvious large-scale flow was observed at depths greater than 3000 dbar. We used transient tracers to estimate isopycnal diffusivity there to be 72±16 m2 s−1. Antarctic Bottom Water in the basin consisted of water masses originating from the Cape Darnley region (0 %–35 %) and Weddell Sea Deep Water (5 %–75 %) diluted by Lower Circumpolar Deep Water above. These snapshot observations not only confirm hydrographic features reported earlier in the Madagascar and Crozet basins, but also describe the diffusive nature of the deep to bottom circulation in the Weddell–Enderby Abyssal Plain