French Research Institute for Exploitation of the Sea
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Observation-only deep learning for gappy satellite-derived ocean colour data using 4DVarNet
No full textMonitoring optical properties of coastal and open ocean waters is crucial to assessing the health of marine ecosystems. Deep learning offers a promising approach to address these ecosystem dynamics, especially in scenarios where gapfree ground-truth data is lacking, which poses a challenge for designing effective training frameworks. Using an advanced neural variational data assimilation scheme (called 4DVarNet), we introduce a comprehensive training framework designed to effectively train directly on gappy data sets. Using the Mediterranean Sea as a case study, our experiments not only highlight the high performance of the chosen neural network in reconstructing gapfree images from gappy datasets but also demonstrate its superior performance over state-of-the-art algorithms such as DInEOF and Direct Inversion, whether using CNN or UNet architecture
Analysis of Export and Transfer Efficiency around the PAP-Site Observatory: an update from the APERO project
No full textPast trajectory of a socio-ecosystem at the land-sea interface: the case of the northern watersheds of the Bay of Brest over the last 150 years
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Tadpole Skin Secretions, Not Food or Temperature, Mediate Costly Cannibal-Induced Plasticity in Invasive Cane Toad Hatchlings
No full textHatchlings of invasive cane toads (Rhinella marina) in Australia respond facultatively to chemical cues of non-feeding cannibalistic conspecific tadpoles by accelerating development, but consequently experience reduced growth, development and survival in the subsequent tadpole stage. Predation-induced developmental acceleration of eggs or hatchlings is rare among amphibians, and the implications of and context-dependent impacts of such developmental plasticity are poorly understood. For cane toads, the source and identity of the tadpole cue that induces this response are unknown. Additionally, it is unknown whether these carry-over costs are due to accelerated early development per se or are specific to developmental acceleration induced by conspecific tadpole cues. Finally, it is unknown whether these costs can be mitigated by the availability of food resources at critical times during early development. We conducted laboratory experiments to investigate these issues. Our results show that (1) based on significant hatchling responses to skin swabs, the chemical that induces costly developmental plasticity is located in the skin of cannibalistic cane toad tadpoles, (2) carry-over effects of early developmental acceleration are elicited only by cues from cannibal tadpoles because temperature-induced developmental acceleration of hatchlings did not reduce subsequent growth, development or survival and (3) excess food availability during early development did not mitigate the carry-over costs of exposure to cannibal tadpole cues. Thus, this developmental plasticity response, triggered by detection of chemicals exuded from the skin of conspecific tadpoles, causes unique negative carry-over costs for younger larvae. However, we found that tadpole production of skin secretions is also plastic, with swabbed tadpoles inducing stronger responses in hatchlings than their unswabbed siblings. Finally, the carry-over costs that follow cannibal exposure cannot be mitigated by favorable nutritional conditions
Which baits for attracting black seabream (Spondyliosoma cantharus) in fish traps?
No full textThe pressure that fishing exerts on marine ecosystems is of increasing concern worldwide. When deployed in compliance with appropriate technical regulations, the use of passive baited gear such as traps is a selective and low-impact fishing technique that can contribute to the sustainable exploitation of marine resources. In the case of traps or lines, the choice of bait might further increase the selectivity of the gear, particularly when the decision is based on the feeding preferences of the target species. In the present study, we investigate the effectiveness of different types of bait in attracting black seabream (Spondyliosoma cantharus), a commercially valuable fish with healthy populations in the Bay of Biscay (France). Specifically, we deployed a baited underwater video camera devoid of trap gear to identify the preferred bait among 10 options selected based on a review of the literature and interviews with recreational and professional fishermen. Because the performance (attractiveness) of a bait might vary depending on how it is assessed, we calculated and compared three indicators to describe the behavior of black seabream in relation to each bait: the number of fish per hour that exhibited Interest or Baited behaviors, with the latter being characterized by an attempt to eat the bait; the amount of time these fish spent in the vicinity of the bait (referred to as time of residence); and the probability that a fish that entered the view of the camera would exhibit Baited behavior (referred to as Baited probability). Cockles were associated with the longest time of residence of Baited fish and presented the highest Baited probability. Lugworm presented the highest time of residence for Interested fish, but the lowest Baited probability. More generally, all baits except an artificial lure demonstrated an ability to attract black seabream, but this tended to decrease with soaking time. The complementarity of the indicators used is discussed, as well as the application of our results to the development of passive baited gear such as fish traps targeting black seabream
Influence of cockle bioturbation on microphytobenthic primary producers: habitat and density-dependent effects
No full textWhile the global impact of the edible cockle Cerastoderma edule on microphytobenthos (MPB) dynamics has been extensively studied, some underlying processes remain unknown, such as their non-trophic interactions. For this purpose, a laboratory mesocosm experimental approach was used to quantify the bioturbation generated by C. edule adults and their influence on oxygen and nutrient fluxes, MPB biomass and photosynthetic performance at the sediment-water interface. The effects of sediment properties and cockle densities (0, 288, 720 and 1,297 ind. m−2) were also investigated. Our results showed that cockles exert a net negative density-dependent effect on MPB biomass, with intensity varying according to sediment type. This is mainly due to sediment reworking by cockles and their emergence at the sediment surface, mechanically disrupting MPB biofilms. Nonetheless, the physiological status and photosynthetic performances of the remaining MPB cells were not impacted. This could be explained by cockle bioirrigation which stimulates nutrient fluxes at the sediment surface and cell turnover. In the finest sediment, the stimulation of MPB growth by nutrient fluxes did not compensate algal biomass loss due to burial, leading to a net decrease in MPB biomass. In coarser sediment, no significant impact of cockles on the net total MPB biomass was observed. This indicates a balance between suboptimal sediment condition for MPB, biofilm destruction by cockles, and enhanced bioirrigation rates that increase nutrient availability for MPB biofilms at the sediment-water interface
Fluids from deep subducted sediments control the seismic behavior of the Lesser Antilles megathrust
No full textAt subduction zones, downgoing topographic features exert first-order structural and hydrologic effect on the plate boundary and the upper plate. Such process has been rarely documented by clear observations, especially at great depths, and it remains elusive how the altered structural and physical characteristics of the upper plate control seismogenic behavior and tectonic evolution of margins. Here, we present a reprocessed multichannel seismic (MCS) profile together with bathymetry and earthquake data in the central Lesser Antilles. A reflector imaged at 15-18 km depth ahead of the Tiburon ridge delimits the base of inner forearc crust with pervasive reflective anomalies. It is interpreted to represent a shallow fluid-rich decollement warped over the rough topography, where the underlying materials consist largely of oceanic sediments identical to those accreted at the Barbados prism and basement fragments from basal erosion. Our results suggest that fluids are expelled upward from the band of subducted sediments, leading to a NW-SE elongated zone of hydrofractured and weakened crust above a serpentinized mantle corner coinciding with a prominent aseismic corridor. The high interplate seismic activity offshore Martinique at ~30–65 km depths may correspond to deeply subducted indurated sediments that act as a strong asperity on the plate interface
