Hélène Tabouret

Spatial and temporal variations in otolith chemistry and relationships with water chemistry: a useful tool to distinguish Atlantic salmon Salmo salar parr from different natal streams.

Otolith elemental (Sr:Ca, Ba:Ca, Mn:Ca, Mg:Ca and Rb:Ca) and isotopic (⁸⁷Sr:⁸⁶Sr) profiles from several annual cohorts of juvenile Atlantic salmon Salmo salar were related to the physico-chemical characteristics (chemical signatures, flow rate, temperature and conductivity) of their natal rivers over an annual hydrological cycle. Only Sr:Ca, Ba:Ca and ⁸⁷Sr:⁸⁶Sr in otoliths were determined by their respective ratios in the ambient water. Sr:Ca ratios in stream waters fluctuated strongly on a seasonal basis, but these fluctuations, mainly driven by water flow regimes, were not recorded in the otoliths. Otolith Sr:Ca ratios remained constant during freshwater residency at a given site and were exclusively related to water Sr:Ca ratios during low flow periods. While interannual differences in otolith elemental composition among rivers were observed, this variability was minor compared to geographic variability and did not limit classification of juveniles to their natal stream. Success in discriminating fish from different sites was greatest using Sr isotopes as it remained relatively constant across years at a given location.

Femtosecond laser ablation ICP-MS measurement of otolith Sr:Ca and Ba:Ca composition reveal differential use of freshwater habitats for three amphidromous Sicyopterus (Teleostei: Gobioidei: Sicydiinae) species

The use of freshwater habitats was examined in three amphidromous goby species of the genus Sicyopterus using otolith microchemistry. Two species were endemic to either New Caledonia or Vanuatu whilst the other was widely distributed. Depositional patterns of strontium (Sr) and barium (Ba) in the otolith of adults were analysed with femtosecond laser ablation inductively coupled plasma mass spectrometry (ICP-MS). The Sr:Ca and Ba:Ca results uncovered three different adult behaviours within the freshwater habitat. Some fishes stayed in elevated locations (square profile); others undertook back-and-forth migrations between higher and lower reaches (up-and-down profile), and finally, others stayed in the lower reaches (constant profile). The consequences of these movements to larval survival or competition for food and territory are discussed. This work brings new knowledge on amphidromous behaviour, and it highlights the necessity of multi-elemental analysis to study amphidromy in freshwater systems.

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)

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 6-8 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.

Simultaneous determination of mercury and butyltin species using a multiple species-specific isotope dilution methodology on the European, Anguilla anguilla glass eel and yellow eel

A methodology to simultaneously determine mercury (MeHg, IHg) and butyltin (TBT, DBT, MBT) compounds in eel samples was assessed and validated using multiple isotopically enriched species. The developed methodology was able to analyse simultaneously the organometal species accurately and precisely and to correct for the potential transformations/degradations of the different species during the various steps of the analytical procedure. Low detection limits were achieved (0.007–0.17 µg Hg kg−1 for mercury (Hg) species and 0.42–0.71 µg Sn kg−1 for tin (Sn) species) allowing analysis of low-mass samples and thus the analysis at the individual organism scale, including glass eels for which samples dry weight ranged from 60 to 100 mg. The methodology was validated with certified reference materials (BCR-464, BCR-477, BCR-710, DOLT-4 and NIST-2977) and applied to the analysis of these pollutants in two developmental stages of the European eel, Anguilla anguilla: individual whole glass eels and muscle tissue from yellow eels. The Adour estuary (South-west France) was selected to monitor the bioaccumulation of organometal species in these organisms, according their developmental stage, their morphological parameters and the sampling site. The results suggest that the accumulation of methylmercury in glass eel tissue is related to weight, with higher concentrations in smaller individuals. Butyltin concentrations were very close to the limit of detection, and no significant differences were detected between glass and yellow eels.

Amphidromy and marine larval phase of ancestral gobioids Rhyacichthys guilberti and Protogobius attiti (Teleostei: Rhyacichthyidae)

Even if amphidromous fish species contribute most to the diversity of fish communities in the tropical insular rivers, their biological cycle remain poorly known. For the first time, the otolith elemental composition and microstructure of two ancestral gobioids, Rhyacichthys guilberti and Protogobius attiti, were investigated to describe their biological cycle and pelagic larval duration (PLD). The otolith analysis using a femtosecond laser ablation coupled to an inductively coupled plasma–mass spectrometer (fs-LA-ICP-MS) revealed an amphidromous life history for R. guilberti and it suggested a progressive habitat shift from a marine habitat to a freshwater environment for P. attiti. For the first time, an endemic species, P. attiti, showed longer and more variable PLD (55.2 ± 13.5 days) than did a widespread one (R. guilberti: ~30 days). These results need to be confirmed by analysing more samples but suggest that factors other than the PLD control endemism and dispersal processes. In association with this first description of the biological cycle for both species, such an approach is a prerequisite for the management and conservation of both patrimonial species.