Aurélie Jolivet

Mineral phase in shell repair of Manila clam Venerupis philippinarum affected by brown ring disease.

The mineral phase of shell repair in the Manila clam Venerupis philippinarum affected by brown ring disease (BRD) was characterised at various scales and at various stages of shell repair by confocal Raman microspectrometry and scanning electron microscopy. Spherulitic and quadrangular aragonite microstructures associated with polyene pigments were clearly observed. Von Kossa staining showed that at the beginning of shell repair, hemocytes are filled with insoluble calcium carbonate salts in all fluids and then are transported toward the extrapallial fluids and the repair sites. Our analyses suggest that after a Vibrio tapetis attack and BRD deposit some clams rapidly cover the deposit, resulting in a modification in the microstructure, which could be produced by the participation of both the mantle and hemocytes.

Clam shell repair from the brown ring disease: a study of the organic matrix using Confocal Raman micro-spectrometry and WDS microprobe

Since 1987, the Manila clam Ruditapes philippinarum has been regularly affected by the brown ring disease (BRD), an epizootic caused by the bacterium Vibrio tapetis. This disease is characterized by the development of a brown deposit on the inner face of valves. While most of the clams die from the BRD infection, some of them are able to recover by mineralizing a new repair shell layer, which covers the brown deposit by a process of encapsulation. The purpose of this work was to study the organic matrix of the shells of Manila clams in the inner shell layer before, during and after the brown deposit and during the shell repair process by confocal Raman micro-spectrometry and wavelength dispersive spectrometry (WDS) microprobe. In addition, the organic matrix of the repaired shell layer was extracted and quantified, by using standard biochemical shell matrix extractions protocols. The brown deposit exhibited high luminescence intensity in Raman spectra, and an increase of S, C, Sr (forming two peaks) and a decrease of Ca, Na concentrations (% w/w), using WDS microprobe mapping and cross-sectional transects. The signature of these trace elements was similar to that recorded on periostracal lamina (% w/w). The high S concentration likely corresponds to the presence of a high amount of sulfated organic compounds. Interestingly, on cross-sectional transects, before the brown deposit, a thin layer of the shell showed also a high luminescence, which may suggest that this layer is modified by bacteria. After the brown deposit, at the beginning of the shell repair process, the luminescence and the S concentration remain high, before declining the level found in non-BRD-affected shells. Quantification of the organic matrix shows that the shell repair layer zone is significantly different from non-BRD-affected shell layer, in particular with a much higher amount of insoluble matrix.

Validation of trophic and anthropic underwater noise as settlement trigger in blue mussels

Like the majority of benthic invertebrates, the blue mussel Mytilus edulis has a bentho-pelagic cycle with its larval settlement being a complex phenomenon involving numerous factors. Among these factors, underwater noise and pelagic trophic conditions have been weakly studied in previous researches. Under laboratory conditions, we tested the hypothesis that picoplankton assimilation by the pediveliger blue mussel larvae acts as a food cue that interacts with anthropic underwater sound to stimulate settlement. We used 13C-labeling microalgae to validate the assimilation of different picoplankton species in the tissues of pediveliger larvae. Our results clearly confirm our hypothesis with a significant synergic effect of these two factors. However, only the picoeukaryotes strains assimilated by larvae stimulated the settlement, whereas the non-ingested picocyanobacteria did not. Similar positive responses were observed with underwater sound characterized by low frequency vessel noises. The combination of both factors (trophic and vessel noise) drastically increased the mussel settlement by an order of 4 compared to the control (without picoplankton and noise). Settlement levels ranged from 16.5 to 67% in 67 h.

Effects of T-bar and DST Tagging on Survival and Growth of European Hake

Controlled experiments were conducted to assess the effects of T-bar and DST tagging on post-release survival and growth of European hake. In this study, two groups of each 30 hake were considered: small fish (SF, average total length: 29.9 cm ± 2.2 cm) and large fish (LF, average total length: 36.4 cm ± 2.5 cm). Within each size group, fish were randomly assigned to one of 3 treatment groups: control (C), T-bar tagging referred as conventional tagging (CT) and DST tagging (DST) with dummy tags. After 4 months, the overall survival rate was 35%. Smaller fish were less impacted by the stress induced by handling, anaesthesia and tagging and in the SF group, the survival rates were similar (30%) for CT or DST. Specific growth rates were highly variable and no significant difference could be observed between control and tagged fish. Our results demonstrate that (1) conventional tagging affects fish survival rates and (2) DST tagging is feasible in the field on “small fish” with expected survival rate and recapture probability close to that of conventional tagging.

Preparation techniques alter the mineral and organic fractions of fish otoliths: insights using Raman micro-spectrometry

The high spatial resolution analysis of the mineral and organic composition of otoliths using Raman micro-spectrometry involves rigorous protocols for sample preparation previously established for microchemistry and trace elements analyses. These protocols often include otolith embedding in chemically neutral resin (i.e., resins which do not contain, in detectable concentration, elements usually sought in the otoliths). Such embedding may however induce organic contamination. In this paper, Raman micro-spectrometry reveals the presence of organic contamination onto the surface obtained from the use of epoxy resin, specifically Araldite. This contamination level varies depending on otolith structures. Core and checks, known as structural discontinuities, exhibit the most important level of contaminations. Our results suggest that otolith embedding with resin affects the organic matrix of the otolith, probably through an infiltration of the resin in the crystalline structure. The interpretation of chemical otolith signatures, especially Raman otolith signatures, and stable isotope analyses should then be revised in light of these results. In this respect, we propose a method for the correction of Raman otolith signatures for contamination effects.

Polar coastal soundscapes: Tridimensional mapping of benthic biophony and ice geophony with a compact sensor array

Polar areas show fast changes linked to global warming. The reduction of the ice pack and the melting of the ice sheet modify the conditions of living of marine fauna. We propose the simultaneous monitoring of the ice and benthic fauna using passive acoustics. Thanks to a compact sensor array of 4 hydrophones (2m*2m*2m), we detected, localized and mapped in three dimensions ({azimuth, elevation} or {x, y, z}) the biophonic and geophonic contributions made up of short and wideband pulses. Tridimensional maps of benthic biophony and ice geophony of Antarctic and Arctic 7 days-long recording sessions (2015, 2016) are built and analyzed over a surface of the order of 1 km2. Benthic invertebrates emit high energetic pulses with peak frequencies ranging from 2 to 55 kHz, most of them below 15 kHz. Geophony is structured into two parts. The ice sheet, located several kilometers or tens of kilometers away, creates a stable spatial distribution of low energetic pulses (representing the majority of pulses in the soundscape) modulated by the temporal variability. The movements of isolated icebergs or pack ice produce localized acoustic events identifiable by the high sound levels and the stable peak frequencies of the emitted pulses.