Dr. Julien Thébault, associate professor

Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer
Laboratoire des Sciences de l'Environnement Marin (UMR6539 UBO/IRD/CNRS)
Office A140
Technopôle Brest-Iroise, Rue Dumont d'Urville
29280 Plouzané
France

Phone: +33 (0) 2 98 49 86 47
Fax: +33 (0) 2 98 49 86 45
E-mail: julien.thebault@univ-brest.frDownload my CV

• Ph.D., Biological Oceanography (sclerochronology), University of Western Brittany, 2002-2005
  
• M.Sc., Marine Biology and Ecology, University of Western Brittany, 1999-2001
  
• B.Sc., Biology of Organisms, University of Rennes I & University of Western Brittany, 1996-1999

• Career
• Research
• Publications
• Teaching
• Miscellaneous
• Master 1 SBM

• Updated: 22/02/2013

Career

My passion for marine biology dates back to my childhood when I spent most of my summer holidays looking at biodiversity in intertidal pools. From junior high school, I knew that my career would revolve around academic research in oceanology. I did my best to reach this goal and started my university studies at the University of Rennes 1 (Rennes, France) and then later at the University of Western Brittany (Brest, France) where I completed the French equivalent to Bachelor's Degree (DEUG + Licence) in Life Sciences & Biology of Organisms (1999). I later completed the French equivalent to Masters of Science (Maîtrise + DEA) in Marine Ecology (2001). My thesis dealt with assessing the potential of using shells of the Chilean scallop Argopecten purpuratus as eulerian archives of coastal environmental variability in the South Pacific Ocean (Rinconada Bay, Chile).

I subsequently registered for doctoral studies and moved for almost two years overseas (Nouméa, New Caledonia) to work at the Institut de Recherche pour le Développement (IRD) on biology, sclerochronology and sclerochemistry of another scallop species, Comptopallium radula. The primary goal was to check if these shells could be good archives of environmental pollution by heavy metals released in the south-west lagoon by ore mining industries and urban development. I defended my Ph.D. in 2005 at the University of Western Brittany. After my doctoral thesis, I have worked for a few months as a research assistant at the European Institute for Marine Studies (IUEM, Brest, France) on a project dealing with the understanding of some geochemical signals (barium and molybdenum concentrations) archived in bivalve mollusk shells (2006).

Then, I felt a desire to work on something different and in 2007, I had the good luck to be invited by Dr. James Cloern from Water Resources Division at U.S. Geological Survey (Menlo Park, CA, USA) to describe primary production and assess the ecological importance of South San Francisco Bay salt ponds for resident and migratory birds. Nothing to do with shells but a nice ecological study on wetland dynamics!

I moved back to Europe during summer 2007 to work as a sclero-scientist with Prof. Bernd Schöne at the University of Mainz, Germany (thanks to a research grant awarded by the Alexander von Humboldt Foundation), on geochemical composition of freshwater (Anodonta cygnea, Germany) and marine (Arctica islandica, Iceland) bivalve shells. I came back to Brest at the end of 2008 for a Teaching and Research Assistant position (A.T.E.R.) during which I worked on structure and functioning of a remote Mauritanian ecosystem (Banc d'Arguin National Park), and sclerochemistry of intertidal bivalve mollusk shells Anadara senilis.

I finally got a permanent Associate Professor position at University of Western Brittany in September 2009, where I hold a chair from the Institut de Recherche pour le Développement. Since then, I teach zoology, biology of populations and ecosystems, marine ecology, and sclerochronology to undergraduate and graduate students, whereas my research at the Laboratoire des Sciences de l'Environnement Marin (LEMAR) currently deals with assessment of anthropogenic and climatic influences on structure and functioning of coastal ecosystems, and especially on phytoplankton dynamics, through geochemical records in mollusk shells from polar, temperate and tropical settings.

Research

The core of my research activities deal with extracting, analyzing and understanding structural (variation of growth increment width) and geochemical (variation of stable isotope ratios and elemental concentrations) proxies archived in shells of freshwater and marine mollusks in order (i) to get information on their life-history traits (growth, longevity, metabolism, reproduction), and (ii) to assess past and present variability of environmental conditions (temperature, salinity, primary production, pollutions, etc.). This scientific field is called sclerochronology, the aquatic equivalent to dendrochronology (study of tree rings). By extension, sclerochemistry is the sub-discipline of sclerochronology dealing with microchemical analyses performed in these biogenic structures.

Mollusk shells are formed by periodic accretion of calcium carbonate crystals (laid down in an organic matrix representing a few percents of the shell weight) at the ventral margin of bivalves and at the peristomial margin of gastropods. In many species, this results in the formation of shell growth increments (corresponding to periods of calcification) separated by growth lines (periods of growth slowdown or cessation). These internal and/or external growth lines reflect annual, monthly, fortnightly, tidal, daily and subdaily rhythms entrained by endogenous oscillators synchronized by environmental cues acting as zeitgebers (time-giver).

(A) Upper surface of the left valve of Pecten maximus (Bay of Brest, France). W1-W4 correspond to winter marks deposited during spring growth restart. (B) External daily growth increments can be observed without any treatment aside from surface cleaning.

These growth lines can then be used as chronological landmarks that provide the basis for assigning precise calendar dates to each successive increment of accreted shell material. Because most mollusks form distinct daily growth lines and grow very fast (tens to hundreds of µm d^-1), they give information on high-frequency variations of (palaeo-)environmental conditions. On another hand, corals and sclerosponges are other widely used biogenic archives that provide useful data on past ecological variability at a seasonal time scale, at most, but that are not suited to reconstruction of processes occurring on short ecological time scales, ranging from days to weeks, such as phytoplankton dynamics. Another advantage of mollusks, and especially bivalves, is that some species are extremely long-lived. For instance, the ocean quahog Arctica islandica can live more than 400 years, a record of longevity for non-colonial animals! Dog cockles Glycymeris glycymeris live up to 200 years, as do freshwater mussels Margaritifera margaritifera. Therefore, in addition to high-resolution palaeoenvironmental reconstruction, bivalve shells can provide very long records of past climatic and environmental variability.

(A) 240-µm thick cross section of a dog cockle shell (Glycymeris glycymeris, Brittany, France) used for sclerochronological analyses, observed under transmitted light. (B) 900-µm thick cross section of the same specimen, used for isotopic analyses and observed under reflected light. Each hole represents one aragonite sample micromilled for stable isotope analysis.

In the past ten years, I have worked on analyzing the rhythm of formation of growth lines of some species with an in situ marking technique, using the calcein fluorochrome. To minimize stress caused by excessive handling, in situ benthic chambers were used for marking experiments. This has been made possible thanks to my qualification as a certified scientific diver (40 m water depth). I have also worked on stable isotope ratios (oxygen and carbon) and trace element concentrations (Mg/Ca, Sr/Ca, Ba/Ca, Mo/Ca, Li/Ca, heavy metals) in many species (scallops, cockles, quahogs, clams, gastropods) from different biogeographic settings (tropical: New Caledonia, Mauritania, Mexico, Florida; temperate: Brittany, Germany, Chile; sub-polar and polar: Canadian Arctic Archipelago, Iceland, and soon, Spitzberg). Most of my work focuses on empirical and experimental calibration of these geochemical proxies (ie. to determine which environmental variable controls incorporation of such and such element or isotope in the shell). A part of these experiments is devoted to improvement of our knowledge on metabolism of these mollusks (ie. respiration and calcification rates). This is done underwater by enclosing live animals under benthic chambers connected (i) to a pump allowing water circulation, and (ii) to a multi-parameter probe continuously measuring temperature, salinity, and oxygen concentration. Repeated incubations over 24-h cycles allow identification of periods of high calcification and respiration rates, which in turn help us to interpret our proxies in the carbonated matrix. And finally, I'm also moving back in the past through the use of these calibrated proxies for palaeoenvironmental reconstructions using long-lived species (dog cockles and freshwater pearl mussels).

Calcein marking of scallops (Comptopallium radula) in the south-west lagoon of New Caledonia.

Measurement of Strombus gigas metabolism using benthic chambers (Xel-Ha lagoon, Yucatan Peninsula, Mexico).

Diving in Mexico... Field trip in Yucatan to improve our knowldege of the biology (diet, respiration) and behaviour (migration patterns) of Strombus gigas, and to use their shells as high-resolution archives of temperature, salinity, primary production, pollution, and groundwater sources.

Scientific production

Peer-reviewed publications

• [18] Thébault J. & Chauvaud L. (2013). Li/Ca enrichments in great scallop shells (Pecten maximus) and their relationship with phytoplankton blooms. Palaeogeography, Palaeoclimatology, Palaeoecology 373: 108-122. [doi:10.1016/j.palaeo.2011.12.014]
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Abstract: Phytoplankton dynamics in coastal oceans is a major component of the global biogeochemical carbon cycle, and is currently affected by global change through modifications in levels of primary productivity and composition of phytoplankton communities. Despite many attempts, no straightforward geochemical proxy has been found yet in marine biogenic carbonates for reconstruction of past phytoplankton dynamics with high temporal resolution. Here, we report on sub-weekly variations of lithium-to-calcium ratios (Li/Ca_shell) along the axis of maximum growth of great scallop shells (Pecten maximus) collected alive between 1999 and 2007 in the bay of Brest, northwest France. Inter-individual variability of Li/Ca_shell time series was very low, suggesting an environmental control on the incorporation of Li within shells. Conversely, inter-annual variability of Li/Ca_shell was high, with limited seasonal Li/Ca_shell variations in 2001 and 2007, and the presence of Li enrichments from May to July in 1999 and 2004. Comparison of these results with shell growth measurements (increment width) and environmental parameters suggests (i) that shell calcification rate is likely the main factor controlling incorporation of Li in Pecten maximus shell calcite, (ii) that seawater temperature has only a weak positive influence on Li/Ca_shell of this species over the range 8-18 °C, and (iii) that during diatom blooms, additional amounts of Li may be trapped in the shell following dissolution of Li-rich frustules of edible species in the digestive tract of scallops, being responsible for Li/Ca_shell peaks. Therefore, we suggest that Li/Ca_shell ratio may be a novel proxy for timing and magnitude of diatom blooms in coastal ecosystems. Analysis of ancient shells may thus provide useful information on past phytoplankton dynamics and on the importance of recent shifts observed from diatoms to non-siliceous phytoplankton in coastal areas affected by anthropogenic activities.



• [17] Royer C., Thébault J., Chauvaud L. & Olivier F. (2013). Structural analysis and paleoenvironmental potential of dog cockle shells (Glycymeris glycymeris) in Brittany, northwest France. Palaeogeography, Palaeoclimatology, Palaeoecology 373: 123-132. [doi:10.1016/j.palaeo.2012.01.033]
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Abstract: To compensate for the lack of high resolution data on variation in environmental parameters before the establishment of monitoring networks, we evaluated dog cockle shells (Glycymeris glycymeris; Mollusca: Bivalvia) as archives for temperature and climate perturbations such as the North Atlantic Oscillation (NAO) over the last 50 years. Oxygen isotope compositions were measured from annual increments of shells collected from the Bay of Brest and the Chausey Islands in northwestern France. Simultaneously, sclerochronological analyses were performed on the same shells. Oxygen isotopic ratios measured in shells collected from the Bay of Brest were compared to in situ temperature and salinity data from monitoring stations and buoys in order to build a specific paleotemperature equation (r²=0.87; p<0.001) for the dog cockle. The specific equation was used to estimate sea surface temperatures around the Chausey Islands between 1966 and 1994. Standardized growth indices (SGI) calculated through sclerochronological methods were strongly correlated to oxygen isotope-derived temperatures. The SGI however did not capture the area's predominant climate pattern, the NAO. This study demonstrates that dog cockle shells can be used for long-term high-resolution reconstructions of past sea surface temperatures.



• [16] Lavaud R., Thébault J., Lorrain A., van der Geest M. & Chauvaud L. (2013). Senilia senilis (Linnaeus, 1758), a biogenic archive of environmental conditions on the Banc d'Arguin (Mauritania). Journal of Sea Research 76: 61-72. [doi:10.1016/j.seares.2012.11.003]
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Abstract: Environmental archives are useful tools for describing past and current climate variations and they provide an opportunity to assess the anthropogenic contribution in coastal ecological changes. Along the West African coast, few studies have focused on such archives in coastal ecosystems. The bloody cockle Senilia senilis, an intertidal bivalve mollusk species, is widely distributed from Western Sahara to Angola, and has been harvested by humans over thousands of years. Therefore, this species appears to be a good candidate for assessing past variations of key environmental parameters such as temperature, primary production, and Saharan dust advection within West African coastal ecosystems. In the present paper, we focused (i) on the identification of growth rhythms of S. senilis shells in Mauritania (Banc d'Arguin), and (ii) on the potential of these shells as (paleo-)environmental archives. The method we used combined environmental survey, sclerochronology, and geochemical analyses of aragonite samples. We showed that microgrowth line formation was controlled by a tidal forcing, leading to the formation of two lines per lunar day. Brightness and thickness of these microgrowth lines progressively decreased from spring to neap tides (fortnightly cycle). Lunar daily growth rates displayed strong seasonal variations, with highest values (> 300 μm per lunar day) recorded in summer. The oxygen isotope composition of S. senilis shells (δ¹⁸O_aragonite) accurately tracked seawater temperature seasonal variations, with an precision of 0.8 °C. Finally, we discussed the opportunity to use Ba:Ca ratio in shells as a proxy for primary production or for Saharan dust transport. We also hypothesized that either Canary Current variations or, more probably, massive aerosol transfers from Sahara to the Atlantic Ocean could control uranium availability in coastal waters and explain the occurrence of U:Ca peaks within S. senilis shells.



• [15] Chauvaud L., Patry Y., Jolivet A., Cam E., Le Goff C., Strand Ø., Charrier G., Thébault J., Lazure P., Gotthard K. & Clavier J. (2012). Variation in size and growth of the great scallop Pecten maximus along a latitudinal gradient. PLoS ONE 7(5): e37717. [doi:10.1371/journal.pone.0037717]
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Abstract: Understanding the relationship between growth and temperature will aid in the evaluation of thermal stress and threats to ectotherms in the context of anticipated climate changes. Most Pecten maximus scallops living at high latitudes in the northern hemisphere have a larger maximum body size than individuals further south, a common pattern among many ectotherms. We investigated differences in daily shell growth among scallop populations along the Northeast Atlantic coast from Spain to Norway. This study design allowed us to address precisely whether the asymptotic size observed along a latitudinal gradient, mainly defined by a temperature gradient, results from differences in annual or daily growth rates, or a difference in the length of the growing season. We found that low annual growth rates in northern populations are not due to low daily growth values, but to the smaller number of days available each year to achieve growth compared to the south. We documented a decrease in the annual number of growth days with age regardless of latitude. However, despite initially lower annual growth performances in terms of growing season length and growth rate, differences in asymptotic size as a function of latitude resulted from persistent annual growth performances in the north and sharp declines in the south. Our measurements of daily growth rates throughout life in a long-lived ectothermic species provide new insight into spatio-temporal variations in growth dynamics and growing season length that cannot be accounted for by classical growth models that only address asymptotic size and annual growth rate.



• [14] Tabouret H., Pomerleau S., Jolivet A., Pécheyran C., Riso R., Thébault J., Chauvaud L. & Amouroux D. (2012). Specific pathways for the incorporation of dissolved barium and molybdenum into the bivalve shell: An isotopic tracer approach in the juvenile great scallop (Pecten maximus). Marine Environmental Research 78: 15-25. [doi:10.1016/j.marenvres.2012.03.006]
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Abstract: Dissolved barium and molybdenum incorporation in the calcite shell was investigated in the Great Scallop Pecten maximus. Sixty six individuals were exposed for 16 days to two successive dissolved Ba and Mo concentrations accurately differentiated by two different isotopic enrichments (⁹⁷Mo, ⁹⁵Mo; ¹³⁵Ba, ¹³⁷Ba). Soft tissue and shell isotopic composition were determined respectively by quantitative ICP-MS (Inductively Coupled Plasma Mass Spectrometer) and laser ablation - ICP-MS. Results from Ba enrichment indicate the direct incorporation of dissolved Ba into the shell in proportion to the levels in the water in which they grew with a 6 to 8 day delay. The low spike contributions and the low partition coefficient (D_Mo = 0.0049±0.0013), show that neither the soft tissue nor the shell were significantly sensitive to Mo enrichment. These results eliminate direct Mo shell enrichment by the dissolved phase, and favour a trophic uptake that will be investigated using the successive isotopic enrichment approach developed in this study.



• [13] Schöne B.R., Wanamaker Jr. A.D., Fiebig J., Thébault J. & Kreutz K. (2011). Annually resolved δ¹³C_shell chronologies of long-lived bivalve mollusks (Arctica islandica) reveal oceanic carbon dynamics in the temperate North Atlantic during recent centuries. Palaeogeography, Palaeoclimatology, Palaeoecology 302(1-2): 31-42. [doi:10.1016/j.palaeo.2010.02.002]
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Abstract: The ability of the ocean to absorb carbon dioxide is likely to be adversely affected by recent climate change. However, relatively little is known about the spatiotemporal variability in the oceanic carbon cycle due to the lack of long-term, high-resolution dissolved inorganic carbon isotope (δ¹³C_DIC) data, especially for the temperate North Atlantic, which is the major oceanic sink for anthropogenic CO₂. Here, we report shell carbon isotope values (δ¹³C_shell), a potential proxy for δ¹³C_DIC, of old-grown specimens of the long-lived bivalve mollusk, Arctica islandica. This paper presents the first absolutely dated, annually resolved δ¹³C_shell record from surface waters of the North Atlantic (Iceland, Gulf of Maine) covering the time interval between 1753 and 2003. According to our results, the δ¹³C_shell data were unaffected by trends related to ontogenetic age. However, the shell carbonate was precipitated with a constant offset from expected equilibrium by − 1.54 to − 2.7 ± 0.2‰ corresponding to a 6.2 to 10.8 ± 0.8‰ contribution of respiratory CO₂ (− 25‰). The offset did not appear to vary through the lifetime of individual specimens and among specimens. Therefore, the δ¹³C_shell data of this species can very likely be used as a measure of δ¹³C_DIC.
Furthermore, shell stable carbon isotope chronologies exhibited habitat-specific differences and a significant inter-annual and decadal variability related to the natural carbon cycle. In addition, a distinct negative δ¹³C_shell shift was found reflecting the oceanic Suess effect, i.e. the admixture of anthropogenic CO₂. However, this shift only occurred after the early 1920s when a major climate regime shift led to a northward movement of the oceanic Polar Front in the Nordic Seas and a large-scale reorganization of atmospheric and oceanic currents in the North Atlantic. This likely resulted in a reduced admixture of cold Polar water onto the North Icelandic shelf (through the East Iceland Current) and the Gulf of Maine (through the Labrador Current) with an increased volume of warmer, isotopically well-equilibrated Atlantic waters. Our shell-based δ¹³C_DIC proxy record provides the basis to quantitatively assess natural and anthropogenically induced patterns of carbon uptake in the North Atlantic.



• [12] Schöne B.R., Zhang Z., Radermacher P., Thébault J., Jacob D.E., Nunn E.V. & Maurer A.-F. (2011). Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells (Arctica islandica) and their function as paleotemperature proxies. Palaeogeography, Palaeoclimatology, Palaeoecology 302(1-2): 52-64. [doi:10.1016/j.palaeo.2010.03.016]
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Abstract: The Sr/Ca and Mg/Ca ratios of many biogenic skeletons provide useful paleotemperature estimates. As yet however, it has remained largely impossible to obtain such information from bivalve shells. In the present study, metal-to-calcium values in the hinge plate (aragonite, outer shell layer) of four ontogenetically old (85 to 374 year-old) specimens of the long-lived bivalve, Arctica islandica, were measured on a LA-ICP-MS. The shells were collected alive in 1868, 1986 and 2003 from three different localities around Iceland. With increasing ontogenetic age and decreasing growth rate, a distinct trend toward increasing Sr/Ca (max. 5.17 mmol/mol) and Mg/Ca values (max. 0.89 mmol/mol) and greater variance were observed. Three potential explanations for these trends include a reduced capacity for element selection due to cell ageing, changing metabolism and/or a relative increase in the number of organic-rich (= Mg-rich) and organic-poor (= Sr-rich) shell portions through ontogeny. Partition coefficients however, remained far below 1, indicating that physiology exerted a strong control over the element partitioning between the shells and the ambient water. After mathematical elimination of these vital effects, residuals exhibited a highly significant negative correlation (e.g., age-detrended Sr/Ca data: R = − 0.64, R² = 0.41, p < 0.0001, growth rate-detrended Mg/Ca data: R = − 0.52, R² = 0.27, p < 0.0001) with sea surface temperature. These results are in good agreement with results obtained from the precipitation of abiogenic aragonite. The results of the present study can help to develop new techniques to extract environmental signals from the metal-to-calcium ratios of bivalve shells.



• [11] Chauvaud L., Thébault J., Clavier J., Lorrain A. & Strand Ø. (2011). What's hiding behind ontogenetic δ¹³C variations in mollusk shells? New insights from the great scallop (Pecten maximus). Estuaries & Coasts 34(2): 211-220. [doi:10.1007/s12237-010-9267-4]
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Abstract: Mollusk shells contain geochemical information about environmental conditions that prevailed at the time of formation. We investigated ontogenetic and seasonal variations of δ¹³C in calcitic shells of Pecten maximus. Ontogenetic variations of δ¹³C_shell in three large specimens collected in Norway, France, and Spain exhibited a similar linear decrease with increasing shell height. We removed this linear drift (detrending). These three residual time series displayed variations that could be linked to environmental fluctuations. To check it, we reanalyzed the isotopic datasets of Lorrain et al. (Journal of Experimental Marine Biology and Ecology 275:47−61, 2002, Geochimica et Cosmochimica Acta 68:3509−3519, 2004), who worked on three scallops harvested in 2000 in the bay of Brest (France), a well-monitored ecosystem. Lowest values of δ¹³C_{shell detrended} were recorded in all shells in late spring−early summer, most likely reflecting corresponding variations in food availability. Our results indicate that ontogenetic and seasonal variations of δ¹³C_shell cannot be used as a proxy for past δ¹³C_DIC variations but should be considered as promising tools for ecophysiological studies.



• [10] Barats A., Amouroux D., Pécheyran C., Chauvaud L., Thébault J. & Donard O.F.X. (2010). Spring molybdenum enrichment in scallop shells: a potential tracer of diatom productivity in temperate coastal environments (Brittany, NW France). Biogeosciences 7(1): 233-245. [doi:10.5194/bg-7-233-2010]
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Abstract: Skeletal molybdenum/calcium ([Mo]/[Ca])_shell ratios were examined in shells of the Great Scallop Pecten maximus collected in temperate coastal environments of Western Europe (42 to 49° N). These ratios were determined by quantitative LA-ICP-MS analyses of daily striae taken every third day (i.e. a temporal resolution of 3 days) in 36 flat valves (2-years old; 3 shells/year). Variations of ([Mo]/[Ca])_shell ratios were significant and reproducible for scallops from the same population, from different years (1998−2004) and temperate coastal locations (NW France). The [Mo]/[Ca])_shell ratios exhibit typical profiles characterized by a background content, below the detection limit for this method (<0.003 μmol/mol) for most of the shell growth period, which is punctuated by a significant transient enrichment (0.031−2.1 μmol/mol) mainly occurring from May to June. The Bay of Brest (France) was investigated in particular because of its long term observations on scallop communities, environmental variables, and high resolution analyses of dissolved Mo in bottom seawater in 2000. In 2000, dissolved Mo exhibited a significant increase in concentration just preceding the maximum ([Mo]/[Ca])_shell ratio. Both the intense monitoring survey in 2000 and over the 7-year period indicates that the ([Mo]/[Ca])_shell maximum is directly influenced by spring changes of environmental conditions at the sediment water interface (SWI), occurring subsequent to the intense and periodic spring bloom. Spring maxima of ([Mo]/[Ca])_shell ratios are closely correlated to the extent of silicic acid and nitrate depletion in seawater between winter and late spring (r²=0.878 and 0.780, p<0.05, n=6) that reflects diatom uptake and productivity in the Bay of Brest. The Mo inputs in bottom waters and subsequent shell enrichment are thus suggested to be directly or indirectly influenced by such biogenic material input at the SWI. The [Mo]/[Ca])_shell records thus reveal unexpected biogeochemical cycles of Mo influenced by coastal spring productivity, faithfully recorded in scallop shells.



• [09] Thébault J., Chauvaud L., L'Helguen S., Clavier J., Barats A., Jacquet S., Pécheyran C. & Amouroux D. (2009). Barium and molybdenum records in bivalve shells: Geochemical proxies for phytoplankton dynamics in coastal environments? Limnology and Oceanography 54(3): 1002-1014. [doi:10.4319/lo.2009.54.3.1002]
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Abstract: Barium : calcium and molybdenum : calcium ratios were investigated in shells of the tropical scallop Comptopallium radula. Three juvenile specimens were harvested alive in the southwest lagoon of New Caledonia after a 1-yr hydrological survey. Calcite samples representing a few hours of biomineralization were laser-ablated along the maximal growth axis and analyzed for Ba and Mo content with an inductively coupled plasma mass spectrometer. Absolute dates of shell precipitation assigned on the basis of periodic formation of shell growth patterns led to the accurate reconstruction of ontogenetic variations of elemental ratios with subweekly resolution. Interindividual variability of Ba : Ca and Mo : Ca time series was low, indicating an environmental control on the incorporation of these elements within shells. Both profiles were characterized by a background level punctuated by sharp peaks. The ingestion of diatoms enriched in Ba (adsorbed on iron oxyhydroxides associated with the frustules) is the most likely cause of the formation of Ba : Ca peaks. Some contribution of diatom-associated barite is also possible. In every instance, Ba : Ca would possibly be a proxy for the timing and magnitude of diatom blooms. Among all the theories that could be advanced to explain the occurrence of Mo : Ca peaks, the most plausible appears to be the ingestion of phytoplankton cells grown on NO₃^-, and therefore containing high levels of Mo required for the activity of nitrate reductase. If this is so, then Mo : Ca could be a new proxy for nitrate uptake by phytoplankton in coastal ecosystems, helping to reconstruct the balance between new and regenerated production in paleoenvironments.



• [08] Thébault J., Schöne B.R., Hallmann N., Barth M. & Nunn E.V. (2009). Investigation of Li/Ca variations in aragonitic shells of the ocean quahog Arctica islandica, northeast Iceland. Geochemistry, Geophysics, Geosystems 10(12): Q12008. [doi:10.1029/2009GC002789]
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Abstract: Interannual and intra-annual variations in lithium-to-calcium ratio were investigated with high temporal resolution in the aragonitic outer shell layer of juvenile Arctica islandica (Mollusca; Bivalvia) collected alive in 2006 off northeast Iceland. Li/Ca_shell ranged between 7.00 and 11.12 μmol mol^-1 and presented well-marked seasonal cycles with minimum values recorded at the annual growth lines; a general pattern was a progressive increase in Li/Ca_shell from March to May, followed by a plateau in June and a decrease down to minimum values in July−August. Li/Ca_shell was correlated with δ¹⁸O_shell-derived temperature, but the strength of this relationship was weak (r² < 0.25 and p < 0.05). It covaried significantly with microgrowth increment width and with the discharge from one of the closest rivers. Seasonal variations of Li/Ca_shell in A. islandica may most likely be explained (1) by calcification rate and/or (2) by significant river inputs of Li-rich silicate particles flowing to the sea as soon as snow melts. In the first case, Li/Ca_shell may be a useful proxy for addressing seasonal variations of growth rate in bivalves that lack discernable microgrowth patterns. Abrupt decreases of Li/Ca_shell may, in turn, help identify growth retardations due to harsh environmental conditions. Alternatively, if Li/Ca_shell variations are linked to particulate Li inputs by rivers, this could be a new proxy for the intensity of mechanical weathering of Icelandic basalts, with interesting perspectives for the reconstruction of frequency and intensity of past jökulhlaups (subglacial outburst floods). Further works, including experimental studies, are needed to test these hypotheses.



• [07] Barats A., Amouroux D., Chauvaud L., Pécheyran C., Lorrain A., Thébault J., Church T.M. & Donard O.F.X. (2009). High frequency barium profiles in shells of the Great Scallop Pecten maximus: a methodical long-term and multi-site survey in Western Europe. Biogeosciences 6(2): 157-170. [doi:10.5194/bg-6-157-2009]
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Abstract: Skeletal barium/calcium ([Ba]/[Ca])_shell ratios were measured every third daily striae in 39 flat valves of the Great Scallop Pecten maximus collected in temperate coastal environments of Western Europe. A methodical evaluation of the ([Ba]/[Ca])_shell ratio was performed for the first time and demonstrates that ([Ba]/[Ca])_shell profiles are reproducible for several scallop individuals from the same population (2-year old; 3 shells/year), over a 7-year period (1998−2004), and from different coastal environments in France (42−49° N). As previously determined in the shells of other bivalve species, ([Ba]/[Ca])_shell profiles generally exhibited a background ratio punctuated by two transient maxima occurring in early and late summer. Background partition coefficient (D_Ba=0.11±0.03, in 2000) was similar to that previously reported in P. maximus shells, suggesting a direct shell uptake of dissolved seawater Ba (Gillikin et al., 2008). The 7-year survey in the Bay of Brest of the high frequency ([Ba]/[Ca])_shell profiles in the scallop's shell was exploited to better constrain both the occurrence and the amplitude of the summer Ba relative enrichments as influenced by environmental processes. Seawater Ba contents in 2000 underlined significant particulate Ba inputs at the sediment water interface (SWI) during ([Ba]/[Ca])_shell peak events. These Ba inputs are thus suggested to be subsequently induced by a pelagic biogenic process, which mainly occurs under summer post-bloom conditions in relationship to the cycling of particulate organic matter and associated Ba. The long term survey reveals that such pelagic Ba cycling processes are responsible for particulate Ba inputs to the sediment water interface (SWI). Subsequent indirect Ba uptake by the bivalve results in higher ([Ba]/[Ca])_shell ratios, in that archived Ba within the shell cannot be used as a direct paleo productivity tracer. Our methodical approach, based on a multi-year and multi-site-survey of ([Ba]/[Ca])_shell ratio in Scallop bivalves, allows us to establish the potential application of such high frequency archives for further biogeochemical and ecological investigations of bivalves in the coastal environment.



• [06] Radermacher P., Schöne B.R., Gischler E., Oschmann W., Thébault J. & Fiebig J. (2009). Sclerochronology - a highly versatile tool for mariculture and reconstruction of life history traits of the queen conch, Strombus gigas (Gastropoda). Aquatic Living Resources 22(3): 307-318. [doi:10.1051/alr/2009043]
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Abstract: The queen conch, Strombus gigas, is an important fisheries resource in the Western Tropical Atlantic. In order to maintain harvesting success, improve fisheries management and contribute to mariculture pursuits, a detailed understanding of the life history traits of this species is required. Traditionally, this has been achieved by tedious and time-consuming long-term field observations. This study presents a highly versatile and rapid technique to estimate the timing and rate of shell growth based on sclerochronology. The Belizean S. gigas specimens (N = 2) from the offshore atoll, Glovers Reef, reached their final shell size (maximum shell height: 22.7 and 23.5 cm, respectively; completed formation of the flared lip) after only two years. However, seasonal growth rates varied considerably. Shells grew up to 6 mm d^-1 during spring (April-June) and fall (September-November) but only 1 to 2 mm d^-1 during July and August. Furthermore, shell growth ceased between December and March. Fastest shell growth occurred nearly contemporaneously with times of maximum precipitation which probably resulted in increased food availability. Slowest shell growth however, occurred during times of reduced rainfall and reduced riverine runoff, i.e. during times of reduced food supply. Sea-water temperature apparently did not exert a major control on shell growth. Notably, the slow winter growth was marked by a distinct purple-colored growth line in the cross-sectioned flared lip. Formation of a second major growth line (brown) fell together with the main reproduction period (late October/early November). Shell microgrowth patterns potentially represent daily or semidiurnal periods but cannot be used to assign exact calendar dates to each shell portion, because they were not visible across the entire cross-section of the whorl. Also, the protruding spines developed on the outer shell surface do not function as time gauges. The time represented by the shell portion between consecutive spines varies greatly from 1 to 72 days. Sclerochronology can potentially facilitate maricultural strategies and aid in site pre-testing and selection to grow S. gigas.



• [05] Thébault J., Schraga T.S., Cloern J.E. & Dunlavey E.G. (2008). Primary production and carrying capacity of former salt ponds after reconnection to San Francisco Bay. Wetlands 28(3): 841-851. [doi:10.1672/07-190.1]
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Abstract: Over 6,110 ha of the commercial production salt ponds surrounding South San Francisco Bay, CA, have been decommissioned and reconnected to the bay, most as part of the largest wetlands restoration program in the western United States. These open water ponds are critical habitat for millions of birds annually and restoration program managers must determine the appropriate balance between retention of ponds versus re-conversion to tidal salt marsh, knowing that both are essential ecosystems for endangered bird species. Our study describes the ecological value of the new open water pond ecosystems as feeding habitats for birds. We used the oxygen rate of change method to determine ecosystem metabolic parameters from high resolution time-series of dissolved oxygen concentration. Areal gross primary production (8.17 g O₂ m^-2 d^-1) was roughly double the world's most productive estuaries. High rates of phytoplankton photosynthesis were balanced by equally high rates of community respiration (8.25 g O₂ m^-2 d^-1). Metabolic equilibrium was delicately poised: sharp irradiance and temperature shifts triggered short term photosynthesis reduction resulting in oxygen depletion. We converted net primary production (NPP) into potential carrying capacity of the forage biota that support targeted pond waterbirds. NPP was processed through both a pelagic food web, resulting in forage biota for piscivorous birds and a benthic food web, resulting in forage biota for shorebirds and diving benthivores. Both food webs included efficient algal-based and inefficient detrital trophic pathways. The result of all primary production being routed through simple food webs was high potential forage production and energy supply to waterbirds, equivalent to 11−163 million planktivorous fish or 19−78 billion small estuarine clams within the 330-ha pond between May and October. Food quantity does not necessarily equal quality and these systems have the potential to produce toxic or inedible algae. Our study provides the first measurement of primary production in the open water ponds of San Francisco Bay and presents a novel approach for transforming primary production into forage production as a metric of an ecosystem's energetic carrying capacity.



• [04] Thébault J., Thouzeau G., Chauvaud L., Cantillánez M. & Avendaño M. (2008). Growth of Argopecten purpuratus (Mollusca: Bivalvia) on a natural bank in Northern Chile: sclerochronological record and environmental controls. Aquatic Living Resources 21(1): 45-55. [doi:10.1051/alr:2008021]
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Abstract: Daily striae on the shell of the scallop, Argopecten purpuratus, were used to investigate its growth in a protected population within La Rinconada Bay, near Antofagasta (2^nd Region, Northern Chile), and to determine how environmental forcings control shell growth. This sclerochronological approach was useful to describe daily shell growth a posteriori. Mean shell growth rates were calculated daily between February and October 1999 from shells of six specimens harvested on 15 October 1999. A multiple regression analysis performed on shell growth and environmental data shows that a temperature increase stimulates shell growth whereas particulate organic carbon concentration might be stressful above 2.5 mg L^-1. The lunar cycle might also have an effect on growth, most potent around New Moons, by synchronizing an endogenous oscillator. The age at commercial size (90 mm) was only 10−11 months in La Rinconada Marine Reserve and the von Bertalanffy growth parameters were K = 2.24 y^-1 and H_∞ = 117 mm. Differences in shell growth performances between this study and previous ones dealing with A. purpuratus growth may be explained by the different methods used for shell growth modelling, higher growth rate on the seabed compared to suspended cultures, and particular environmental forcings (e.g. El Niño Southern Oscillation-ENSO events). Growth performance seems better during La Niña than during El Niño events, probably because of the large temperature increase (above the highest temperatures recorded in normal conditions) and the decline in coastal upwelling (which affects food availability) during El Niño. La Rinconada Marine Reserve appears as a very favourable site for A. purpuratus growth, probably because of the active upwelling zone off Antofagasta. These new insights on A. purpuratus shell growth confirm the importance of La Rinconada Marine Reserve as an area supporting repopulation of endangered wild stocks and scallop aquaculture in Chile.



• [03] Thébault J., Chauvaud L., Clavier J., Guarini J., Dunbar R.B., Fichez R., Mucciarone D.A. & Morize E. (2007). Reconstruction of seasonal temperature variability in the tropical Pacific Ocean from the shell of the scallop, Comptopallium radula. Geochimica et Cosmochimica Acta 71(4): 918-928. [doi:10.1016/j.gca.2006.10.017]
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Abstract: We investigated the oxygen isotope composition (δ¹⁸O) of shell striae from juvenile Comptopallium radula (Mollusca; Pectinidae) specimens collected live in New Caledonia. Bottom-water temperature and salinity were monitored in-situ throughout the study period. External shell striae form with a 2-day periodicity in this scallop, making it possible to estimate the date of precipitation for each calcite sample collected along a growth transect. The oxygen isotope composition of shell calcite (δ¹⁸O_{shell calcite}) measured at almost weekly resolution on calcite accreted between August 2002 and July 2003 accurately tracks bottom-water temperatures. A new empirical paleotemperature equation for this scallop species relates temperature and δ¹⁸O_{shell calcite}:

t(°C)=20.00(±0.61) - 3.66(±0.39) × (δ¹⁸O_{shell calcite VPDB} - δ¹⁸O_{water VSMOW})

The mean absolute accuracy of temperature estimated using this equation is 1.0 °C at temperatures between 20 and 30 °C. Uncertainties regarding the precise timing of CaCO₃ deposition and the actual variations in δ¹⁸O_water at our study sites probably contribute to this error. Comparison with a previously published empirical paleotemperature equation indicates that C. radula calcite is enriched in ¹⁸O by ∼0.7‰ relative to equilibrium. Given the direction of this offset and the lack of correlation between shell growth rate and δ¹⁸O_{shell calcite}, this disequilibrium is unlikely to be related to kinetic isotope effects. We suggest that this enrichment reflects (1) a relatively low pH in the scallop's marginal extrapallial fluid (EPF), (2) an isotopic signature of the EPF different from that of seawater, or (3) Rayleigh fractionation during the biocalcification process. Relative changes in δ¹⁸O_{shell calcite} reflect seawater temperature variability at this location and we suggest that the shell of C. radula may be useful as an archive of past seawater temperatures.



• [02] Thébault J., Chauvaud L., Clavier J., Fichez R. & Morize E. (2006). Evidence of a 2-day periodicity of striae formation in the tropical scallop Comptopallium radula using calcein marking. Marine Biology 149(2): 257-267. [doi:10.1007/s00227-005-0198-8]
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Abstract: The periodicity of striae formation in the tropical scallop Comptopallium radula (Indo-West Pacific Ocean) was investigated with an in situ marking technique, using the calcein fluorochrome. To minimize scallop stress caused by excessive handling, in situ benthic chambers were used for marking experiments. Once marked, scallops (shell height range: 38.4−75.8 mm) remained on site in a large benthic enclosure and were collected at regular time intervals to count new striae formed after marking, over a period of 3 months. A 3-h exposure period with calcein (150 mg l^-1) was sufficiently long to create a detectable mark in nearly all shells. It was, however, impossible to count the striae in 48.2% of the shells (mainly large specimens) because of a very small growth after marking. Lack of significant mortality during the experiments indicated that tested calcein concentrations were not lethal. A decrease in shell growth rate was observed after marking but the respective impacts of calcein toxicity and changes in environmental conditions could not be discriminated. Our results suggest that in situ calcein marking inside benthic chambers is suitable for shell growth studies of scallops, provided the latter are not too old. After marking, the juvenile C. radula formed an average of one stria every 2.1 days in summer. Reports of 2-day periodicity in biological rhythms are rare. Striae formation in C. radula may be controlled by an endogenous oscillator, synchronized by an environmental cue acting as a zeitgeber, such as seawater temperature or sea level pressure, both of which exhibit 2-day variations in the Pacific Ocean. As in many other scallop species, C. radula forms striae periodically under natural conditions, but this study shows that in pectinid juveniles, this periodicity can deviate from a daily cycle. These results suggest that C. radula shells have tremendous potential for recording environmental conditions during periods ranging from months to a few years and with a resolution of 2 days.



• [01] Fichez R., Adjeroud M., Bozec Y.-M., Breau L., Chancerelle Y., Chevillon C., Douillet P., Fernandez J.-M., Frouin P., Kulbicki M., Moreton B., Ouillon S., Payri C., Perez T., Sasal P. & Thébault J. (2005). A review of selected indicators of particle, nutrient and metal inputs in coral reef lagoon systems. Aquatic Living Resources 18(2): 125-147. [doi:10.1051/alr:2005015]
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Abstract: This review presents environmental and biological indicators of the impact of three major categories of inputs in coral reef lagoons i.e. particles, nutrients and metals. Information was synthesized to extract well established indicators together with some interesting new concepts currently under development, and to provide the reader with an assessment of their respective advantages and drawbacks. The paper has been organized according to the capacity of three categories of indicators to respond either in a specific or a non specific way to a given source of input. The first section focuses on abiotic indicators which main interest is to respond instantaneously and in a truly specific way to a given source of input. The second and third sections present informations on bioindicators either at the sub-individual level or at the individual to community level, indicator specificity generally decreasing as a direct function of biological or ecological complexity. This review showed that even though significant work has already been done on coral reef ecosystems, much more scientific studies are still needed to answer the growing local demands for simple and truly validated tools to be used in environmental surveys. It is further stressed that, due to the biological and environmental diversity of coral reef lagoons, a preliminary step of on-site validation must be considered as an absolute prerequisite when indicators are planned to be used in the frame of a local environmental monitoring programme.

Reviews

I served as a reviewer for the following journals:

• Palaios
• Geochemical Journal
• Aquatic Living Resources
• Palaeogeography, Palaeoclimatology, Palaeoecology
• Restoration Ecology

Ph.D. thesis

• Thébault J. (2005). The shell of the scallop, Comptopallium radula (Bivalvia; Pectinidae), Eulerian high-frequency archives of the variability of tropical coastal environments (Pacific Ocean). Ph.D. thesis, Université de Bretagne Occidentale, Brest, France, 378 pp.
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Abstract: Coastal ecosystems are exposed to many disturbances leading to the alteration of their structure and functioning. In order to assess the respective roles of natural variability and anthropogenic influences on this process, and to predict the future state of these ecosystems more accurately, we must be able to reconstruct the past variations of certain parameters (ocean temperature, biological productivity, contaminant inputs, etc.) prior to any major anthropogenic influence. Instrumental measurements of these parameters are, however, fairly recent and the reconstruction of the variability of coastal ecosystems prior to the Industrial Revolution can only be done by using proxies embedded in the available archives.

This Ph.D. dissertation focuses on the use of the shell of Comptopallium radula, a tropical bivalve of the mollusc family Pectinidae, for the reconstruction of environmental variability in the southwest lagoon of New Caledonia, an ecosystem influenced by multiple stresses (global warming, urbanization, opencast mining). This work is based on the comparison of geochemical data archived in the scallop shell through ontogeny, with several physical, chemical, and biological variables measured in the lagoon (weekly environmental survey). The aim of this approach is to calibrate and to make use of different climatic and environmental proxies.

Calcein markings, performed in situ on juvenile scallops, demonstrated that the growth striae wrinkling the external surface of C. radula's shell are formed with a 2-day periodicity.

Isotopic analyses (δ¹⁸O and δ¹³C) were performed on calcite micro-samples collected along the maximal growth axis of 6 juvenile shells. Based on the periodicity of stria formation, a calendar date was accurately assigned to each sample (weekly resolution). Our results indicate that the ontogenetic variations of δ¹⁸O_calcite allow the reconstruction of seawater temperature with a mean accuracy of 1 °C. The carbon isotope composition (δ¹³C_calcite) cannot, however, be used as a proxy for the pelagic primary production as its variations could be controlled by the benthic metabolism (sediment and corals).
Following these isotopic analyses, elemental analyses were performed on the same shells using a laser ablation system coupled to an inductively coupled plasma mass spectrometer (LA-ICP-MS). Through the use of skeletal trace metal concentrations, our results show that C. radula cannot be used as a biomonitor of metal inputs in the lagoon: the ontogenetic variations of these concentrations probably reflect high-frequency temporal variations of metal fluxes at the sediment-water interface. As for barium and molybdenum, their skeletal concentrations may be used as proxies for the biomass of diatoms and diazotrophs, respectively.

This study points out the considerable potential of the shell of C. radula as a high-frequency Eulerian archive of climatic and environmental variability in the southwest lagoon of New Caledonia. It also highlights the major role of benthic processes in the incorporation of geochemical signals in the calcitic matrix of the shell. Its use as a paleoceanographic tool is now governed by the discovery of fossil beds of the species.

Contributions to international conferences

• [24] Gaillard B., Pérez V., Olivier F., Tremblay R., Meziane T., Neumeier U., Thébault J. & Chauvaud L. (2012). Population dynamics of Venus verrucosa (L.) in the Chausey Archipelago. Physiomar 2012, Santiago de Compostela, Spain, September 4-8, 2012 (Poster).


• [23] Pérez V., Meziane T., Tremblay R., Thébault J., Chauvaud L. & Olivier F. (2012). Trophic resources of Venus verrucosa (L.) in the Chausey Archipelago. Physiomar 2012, Santiago de Compostela, Spain, September 4-8, 2012 (Oral presentation).


• [22] Leynaert A., Hégaret H., Beker B., Chatterjee A., Lelong A., Long M., Lavaud R., Thébault J., Amice E. & Chauvaud L. (2012). Role of the benthic community in domoic acid accumulation of great scallop Pecten maximus. Physiomar 2012, Santiago de Compostela, Spain, September 4-8, 2012 (Oral presentation).


• [21] Gaillard B., Olivier F., Thébault J., Archambault P., Bélanger S., Chauvaud L., Gosselin M., Martel A., Meziane T. & Tremblay R. (2012). Structural analyses and paleoenvironmental potential of Astarte moerchi in the Canadian Arctic. International Polar Year 2012 Conference, Montréal, Canada, April 22-27, 2012 (Oral presentation).


• [20] Stieglitz T., Chauvaud L., Amice E., Thébault J., Peel J., Aldana-Aranda D. & Enriquez Diaz M. (2011). Habitat usage of a groundwater-fed coastal inlet by the iconic and endangered queen conch Strombus gigas, Yucatan Peninsula, Mexico. IUGG 2011 25^th International Union of Geodesy and Geophysics General Assembly, Melbourne, Australia, June 28 - July 7, 2011 (Oral presentation).


• [19] Schöne B.R., Wanamaker Jr. A.D., Fiebig J., Thébault J. & Kreutz K.J. (2010). Annually resolved oceanic carbon dynamics in the temperate North Atlantic during recent centuries. AGU Fall Meeting, San Francisco, CA, USA, December 13-17, 2010 (Oral presentation).


• [18] Schöne B.R., Wanamaker Jr. A.D., Fiebig J., Thébault J. & Kreutz K.J. (2010). Annually resolved δ¹³C_shell chronologies of long-lived bivalve mollusks (Arctica islandica) reveal oceanic carbon dynamics in the temperate North Atlantic during recent centuries. GeoDarmstadt 2010, Darmstadt, Germany, October 10-13, 2010 (Oral presentation).


• [17] Chauvaud L., Thébault J., Clavier J., Lorrain A. & Strand Ø. (2010). What's hiding behind ontogenetic δ¹³C variations in mollusk shells? New insights from the great scallop (Pecten maximus). 2^nd International Sclerochronology Conference, Mainz, Germany, July 24-28, 2010 (Oral presentation).


• [16] Thébault J., Schöne B.R., Chauvaud L., Hallmann N., Richard M., Barth M., Nunn E.V. & Bassoullet C. (2010). Investigation of Li/Ca ratio temporal variations in shells of two marine bivalves: Arctica islandica (Iceland) and Pecten maximus (France). 2^nd International Sclerochronology Conference, Mainz, Germany, July 24-28, 2010 (Oral presentation).


• [15] Poulain C., Lorrain A., Thébault J., Gillikin D.P., Munaron J.-M., Bohn M., Robert R. & Paulet Y.-M. (2010). The impact of solution chemistry on the incorporation of Mg, Sr and Ba in the aragonite shell of Ruditapes philippinarum: results from a laboratory study. 2^nd International Sclerochronology Conference, Mainz, Germany, July 24-28, 2010 (Oral presentation).


• [14] Schöne B.R., Zhang Z., Radermacher P., Thébault J., Jacob D.E., Nunn E.V. & Maurer A.-F. (2010). Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells (Arctica islandica) and their function as paleotemperature proxies. 2^nd International Sclerochronology Conference, Mainz, Germany, July 24-28, 2010 (Oral presentation).


• [13] Radermacher P., Gischler E., Oschmann W., Thébault J. & Fiebig J. (2010). Sclerochronology: a highly versatile tool for mariculture and reconstruction of life history traits of the queen conch, Strombus gigas (Gastropoda). 2^nd International Sclerochronology Conference, Mainz, Germany, July 24-28, 2010 (Poster).


• [12] Tabouret H., Carlier A., Thébault J., Pécheyran C., Chauvaud L. & Amouroux D. (2010). Isotopic approach to assess dissolved Mo and Ba uptake in scallop shell: new insights into the use of Mo/Ca and Ba/Ca ratios as proxies in temperate coastal environment. 2^nd International Sclerochronology Conference, Mainz, Germany, July 24-28, 2010 (Poster).


• [11] Thébault J., Chauvaud L., L'Helguen S., Clavier J., Barats A., Pécheyran C. & Amouroux D. (2010). Barium and molybdenum records in shells of Comptopallium radula (Bivalvia; Pectinidae): high-resolution proxies for phytoplankton dynamics in the coral reef lagoon of New Caledonia. 2^nd International Sclerochronology Conference, Mainz, Germany, July 24-28, 2010 (Poster). Award of the best non-student poster


• [10] Radermacher P., Schöne B.R., Gischler E., Oschmann W., Thébault J. & Fiebig J. (2010). Sclerochronology - a highly versatile tool for mariculture and reconstruction of life history traits of the queen conch, Strombus gigas (Gastropoda). EGU General Assembly 2010, Vienna, Austria, May 2-7, 2010 (Poster).


• [09] Chauvaud L., Lorrain A., Thébault J., Gillikin D.P., Paulet Y.-M., Strand Ø., Blamart D., Guarini J.-M. & Clavier J. (2008). What's hiding behind ontogenetic δ¹³C variations in mollusc shells: New insights from scallops. AGU Fall Meeting, San Francisco, USA, December 15-19, 2008 (Poster).


• [08] Richard M., Chauvaud L., Benoît M., Thébault J., L'Helguen S., Maguer J.-F., Hémond C., Agranier A., Bassoullet C. & Sinquin G. (2008). Quantitative analyses of trace elements with HR-ICP-MS Element2: An example of application in shells of the Great Scallop Pecten maximus. AGU Fall Meeting, San Francisco, USA, December 15-19, 2008 (Poster).


• [07] Schöne B.R., Wanamaker Jr. A.D., Fiebig J., Thébault J. & Kreutz K.J. (2008). Shells of Arctica islandica suggest sluggish response of temperate North Atlantic to rise of anthropogenic CO₂. Joint Annual Meeting of the Geological Society of America (GSA), Houston, Texas, USA, October 5-9, 2008 (Oral presentation).


• [06] Schraga T.S., Thébault J., Cloern J.E. & Dunlavey E.G. (2008). Green biomass machines: The former salt ponds of South San Francisco Bay. 2008 South Bay Science Symposium, San Jose, California, USA, September 25, 2008 (Poster).


• [05] Thébault J., Schraga T.S. & Cloern J.E. (2007). Unintended aquaculture: Productivity in a South San Francisco Bay salt pond (California). 19^th Biennial Conference of the Estuarine Research Federation, Providence, USA, November 4-8, 2007 (Poster).


• [04] Fichez R., Chevillon C., Chifflet S., Douillet P., Dupouy-Douchement C., Faure V., Fernandez J.-M., Gérard P., Hédouin L., Jouon A., Le Borgne R., Lefebvre J.P., Mari X., Moreton B., Ouillon S., Pringault O., Rochelle-Newall E., Thébault J., Torréton J.-P. & Viret H. (2005). Camelia Research Unit: Characterisation and modelling of exchanges in lagoons subject to terrigeneous and anthropogenic influences. 1^st International Workshop on Organic Matter Modeling, Toulon, France, November 16-18, 2005 (Poster).


• [03] Thébault J., Clavier J., Chauvaud L., Fichez R., Amouroux D. & Barats A. (2005). The shell of the tropical scallop Comptopallium radula: Archives of siliceous and cyanobacterial pelagic primary production? ASLO Summer Meeting, Santiago de Compostela, Spain, June 19-24, 2005 (Oral presentation).


• [02] Thébault J., Chauvaud L., Clavier J., Dunbar R.B., Fichez R. & Mucciarone D.A. (2005). Use of oxygen isotope thermometry for the calibration of the scallop Comptopallium radula as a high-resolution temperature recorder in New Caledonia. ASLO Aquatic Sciences Meeting, Salt Lake City, USA, February 20-25, 2005 (Oral presentation).


• [01] Thébault J., Fichez R., Clavier J., Chauvaud L. & Peignon C. (2003). Bioaccumulation of trace elements in the scallop Comptopallium radula in the south-west lagoon of New Caledonia. International Meeting on Preservation and Ecological Restoration in Tropical Mining Environments, Nouméa, New Caledonia, July 15-20, 2003 (Poster).

Teaching

My first teaching opportunity was offered by Prof. Schöne in 2007. He proposed me to give lectures in his course Einführung in die Paläontologie (standing for Introduction to Paleontology). Most of these undergraduate students had a geosciences background. To open their minds to new ideas, I created a course related to paleontology, but with chips of marine ecology: Carbon cycle and paleoproductivity: Influence of phytoplankton on climate. The very positive feedbacks from these students, who didn't know before what was phytoplankton, convinced me of the validity of a multidisciplinary approach in teaching.

The pleasure I took in preparing and giving this lecture incited me to follow up on this track and I applied for assistant (2008-2009) and then permanent associate professor positions (since 2009) at the University of Western Brittany. Since then, I teach zoology to undergraduate students, focusing my lectures on developmental biology and entomology. I also give lectures to students in their 2^nd year of B.Sc. in order to introduce them to marine ecology (general overview of the marine realm, interactions between marine organisms, main marine ecosystems, impact of oil spills). My lectures in biology of populations are focused on evolutionary biology (selection and evolution of life history traits) and conservation biology.

Although an important part of my teaching activity takes place in lecture halls, I also feel field excursions are essential to be closer to students and to show them a less boring side of university studies! So I spend some time with students in the field, especially for assessment of river biological quality through the use of macroinvertebrate communities (mostly insect larvae). In the future, I would like to organize longer field trips (a week or so) devoted to different aspects of zoology and ecology (marine diversity, botany, ornithology, etc.).

One of my favorite course is the one I give to graduate students (2^nd year of M.Sc.) on Biological Records of Environment. With good colleagues, we introduce them to sclerochronology and sclerochemistry, on fish otoliths, mollusk shells, and other biogenic archives. We expose them to peer-reviewed articles on these topics, that they must read, criticize, and summarize through oral presentations with slide shows. They really like this and I feel it is the perfect way to introduce them to a future career in academic research.

The rest of my teaching activity consists in training master students (1^st and 2^nd year of M.Sc.) and Ph.D. students to scientific research, mostly in sclerochronology and chemistry of mollusk shells.

Finally, I supervise the 1^st year of the Marine and Coastal Sciences Master program (speciality Marine Biological Sciences - SBM).

Courses taught:

B.S. in Biology:

• 1^st year:
  • L1 BOP/BCP: Zoology
  • L1 BioSTU: General Biology
• 2^nd year:
  • L2 BOP/BioSTU: General Ecology
• 3^rd year:
  • L3 BOP: Biology of Populations and Ecosystems
  • L3 Bio-STU: Animal and Vegetal Biology
  • L3 BOP/Bio-STU: Methods in Ecology

M.S. in Marine and Coastal Sciences (Master SML), speciality Marine Biological Sciences (SBM):

• 1^st year:
  • M1 SML-SBM: Biology of Aquatic Populations
• 2^nd year:
  • M2 SML-SBM: Biological Records of Environment

Student research projects:

• Adhitya Kusuma Wardana, 2012, Diponegoro University (Semarang, Indonesia) & University of Western Brittany (M.S. Marine Biological Sciences): Sclerochronological investigation on ecology and life-history traits of a reef gastropod Trochus niloticus: comparison of populations from New Caledonia and Vanuatu


• Clémentine Le Jouan, 2012, University of Western Brittany (M.S. Marine Biological Sciences): Investigation of the response of primary consumers to the Deepwater Horizon oil spill using sclerochemical analyses of Louisiana oyster shells, Crassostrea virginica


• Clémence Royer, 2011-2014, University of Western Brittany (Ph.D. Biological Oceanography): Palaeoecological reconstruction of the impact of anthropogenic activities on aquatic ecosystems of the Bay of Brest and its watersheds: sclerochronological and geochemical investigations on shells of the freshwater pearl mussel (Margaritifera margaritifera) and the dog cockle (Glycymeris glycymeris)


• Blandine Gaillard, 2011, University of Western Brittany (M.S. Marine Biological Sciences): Sclerochronology and sclerochemistry of deep-water bivalve shells of Astarte moerchi in the Canadian Arctic


• Romain Lavaud, 2010, University of Western Brittany (M.S. Marine Biological Sciences): Assessing the potential of bloody cockle shells, Anadara senilis, as environmental archives of ecological functioning of the Banc d'Arguin ecosystem (Mauritania)


• Clémence Royer, 2010, University of Western Brittany (M.S. Marine Biological Sciences): Structural analysis and paleoenvironmental potential of dog cockle (Glycymeris glycymeris) in Brittany

Miscellaneous

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