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Bibliographie de l'Institut Maurice-Lamontagne

Sonia MICHAUD

LIZOTTE, M., M. LEVASSEUR, S. MICHAUD, M.G. SCARRATT, A. MERZOUK, M. GOSSELIN, J. POMMIER, R.B. RIVKIN, R.P. KIENE, 2012. Macroscale patterns of the biological cycling of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in the Northwest Atlantic. Biogeochemistry, XX(X): XX-XX Article in press.

LUCE, M., M. LEVASSEUR, M.G. SCARRATT, S. MICHAUD, S.-J. ROYER, R. KIENE, C. LOVEJOY, M. GOSSELIN, M. POULIN, Y. GRATTON, M. LIZOTTE, 2011. Distribution and microbial metabolism of dimethylsulfoniopropionate and dimethylsulfide during the 2007 Arctic ice minimum. J. Geophys. Res. (C Oceans), 116(11). Art. no C00G06, 8 p.

[Résumé disponible seulement en anglais]
The distribution and biological cycling of the climate active trace gas dimethylsulfide (DMS) and its algal precursor dimethylsulfoniopropionate (DMSP) were characterized at 20 stations across the Canadian High Arctic during fall 2007. Transformation rates of DMSP and production rates of DMS from dissolved DMSP (DMSPd) were measured during 3 h onboard incubations with radioactively labeled 35S-DMSP. Particulate DMSP (DMSPp) in surface waters varied between 2 and 39 nmol L-1 and increased with chlorophyll a (Chl a) concentrations (r = 0.84). DMS concentrations in surface waters ranged from 0.05 to 0.8 nmol L-1 and were positively correlated with DMSPp (r = 0.89) and Chl a (r = 0.74). The DMSPd loss rate constant varied from 0.01 to 0.14 h-1 and was also positively correlated with Chl a concentrations (r = 0.67). The turnover time of the DMSPd pool varied between 0.3 and 3.4 days (mean = 0.96 day). Bacterial DMS production varied between 0.01 and 0.51 nmol L-1 d-1 (mean = 0.14 nmol L-1 d-1). Assuming local steady state conditions at the time scale of a day, the turnover time of the DMS pool based only on production from DMSPd was ˜6 days at the sampling stations. This long turnover time suggests that DMS production was dominated by nonbacterial processes during our study. Our results show that DMS production could persist at low rates in late fall under ice-free conditions. The magnitude of this production appears to be limited by the low algal and bacterial production prevailing at that time.© 2011 American Geophysical Union

REMPILLO, O., A.M. SEGUIN, A.-L. NORMAN, M. SCARRATT, S. MICHAUD, R. CHANG, S. SJOSTEDT, J. ABBATT, B. ELSE, T. PAPAKYRIAKOU, S. SHARMA, S. GRASBY, M. LEVASSEUR, 2011. Dimethyl sulfide air-sea fluxes and biogenic sulfur as a source of new aerosols in the Arctic fall. J. Geophys. Res. (D Atmospheres), 116(24): art. no. D00S04.

[Résumé disponible seulement en anglais]
Dimethyl sulfide (DMS) and its oxidation products, which have been proposed to provide a climate feedback mechanism by affecting aerosol and cloud radiative properties, were measured on board the Canadian Coast Guard ship Amundsen in sampling campaigns in the Arctic in the fall of 2007 and 2008. DMS flux was calculated based on the surface water measurements and yielded 0.1–2.6 μmol m-2 d-1 along the Northwest Passage in 2007 and 0.2–1.3 μmol m-2 d-1 along Baffin Bay in 2008. DMS oxidation products, sulfur dioxide (SO2), methane sulfonic acid (MSA), and sulfate in aerosols were also measured. The amounts of biogenic SO2 and sulfate were approximated using stable isotope apportionment techniques. Calculating the threshold amount of SO2 needed for significant new particle formation from the formulation by Pirjola et al. (1999), the study suggests that instances of elevated biogenic SO2 concentrations (between 8 and 9 September 2008) derived using conservative assumptions may have been sufficient to form new aerosols in clean air conditions in the Arctic region.© 2011 American Geophysical Union

CHANG, R.Y.-W., S.J. SJOSTEDT, J.R. PIERCE, T.N. PAPAKYRIAKOU, M.G. SCARRATT, S. MICHAUD, M. LEVASSEUR, W.R. LEAITCH, J.P.D. ABBATT, 2011. Relating atmospheric and oceanic DMS levels to particle nucleation events in the Canadian Arctic. J. Geophys. Res. (D Atmospheres), 116(21): art. no. D00S03.

[Résumé disponible seulement en anglais]
Measurements of ocean surface and atmospheric dimethyl sulfide (DMS) and particle size distributions were made in the Canadian Arctic Archipelago during the fall of 2007 and the late summer of 2008 aboard the Canadian Coast Guard Ship Amundsen. Nucleation-mode particles were observed during the 2008 cruise, which took place in the eastern Arctic from August to September when the atmosphere and ocean were more photo-active as compared to the October 2007 transit in the Beaufort Sea during which no nucleation/growth events were observed. The observed nucleation periods in 2008 coincided with high atmospheric and ocean surface DMS concentrations, suggesting that the particles originated from marine biogenic sources. An aerosol microphysics box model was used to simulate nucleation given the measured conditions in the marine boundary layer. Although other sources may have contributed, we find that the newly formed particles can be accounted for by a marine biogenic DMS source for combinations of the following parameters: [OH] ≥ 3 × 105 molecules cm-3, DMS mixing ratio is ≥ 100 pptv, the activation coefficient is ≥ 10-7 and the background particle concentration is ≥ 100 cm-3.©2011American Geophysical Union

BOURDAGE, H., P. GOUDREAU, 2010. Évaluation des stocks de pétoncles des eaux côtières du Québec en 2009 : données de la pêche commerciale ; Stock assessment on scallops of the inshore waters of Quebec in 2009: commercial fishery data. MPO, Secrétariat canadien de consultation scientifique, Document de recherche ; DFO, Canadian Science Advisory Secretariat, Research Document, 2010/068, viii + 69 p.

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Ce document présente les indicateurs de la pêche commerciale ayant servi à l’évaluation des stocks de pétoncles des eaux côtières du Québec suivant les saisons de pêche 2007 à 2009. Ce processus régional de revue s'est déroulé le 26 janvier 2010 à l'Institut Maurice-Lamontagne, à Mont-Joli. Lors de cette rencontre, l'assemblée a revu l'état des stocks exploités commercialement dans la région du Québec. Ce document de recherche présente donc les méthodologies et les données qui ont été présentées au moment de la revue pour les statistiques de pêche et l’échantillonnage des captures commerciales.

ROYER, S.-J., M. LEVASSEUR, M. LIZOTTE, M. ARYCHUK, M.G. SCARRATT, C.S. WONG, C. LOVEJOY, M. ROBERT, K. JOHNSON, A. PENA, S. MICHAUD, R.P. KIENED, 2010. Microbial dimethylsulfoniopropionate (DMSP) dynamics along a natural iron gradient in the northeast subarctic Pacific. Limnol. Oceanogr., 55(4): 1614-1626.

[Résumé disponible seulement en anglais]
We characterized the effect of an inshore–offshore gradient in Fe in the northeast subarctic Pacific on the bacterioplankton and phytoplankton assemblages and on the microbial cycling of particulate and dissolved dimethylsulfoniopropionate (DMSPp and DMSPd) and dimethylsulfide (DMS). Averaged concentrations of total dissolved Fe (TDFe) decreased linearly with increasing water density along the transect, from 3.4 nmol L-1 at the two inshore stations to 1.0 nmol L-1 at the offshore stations, as a result of the vertical and lateral mixing between the Fe-rich coastal water and the Fe-poor Alaska Current. The Fe-rich inshore stations were dominated by diatoms and characterized by low DMSPp : chlorophyll a (Chl a) ratios (ca. 26 nmol μg-1) and bacterial DMS yield (< 4 %). In contrast, the Fe-poor offshore stations were dominated by prymnesiophytes and exhibited high DMSPp : Chl a ratios (ca. 84 nmol μg-1) and bacterial DMS yield (8 %). Chl a, DMSPp, and the abundance of total bacteria and three bacterial clades (Gammaproteobacteria, Roseobacter, and Betaproteobacteria) were positively correlated with the TDFe gradient. At the Fe-poor offshore stations, the positive correlation found between TDFe and the DMSPp : Chl a ratios suggests that Fe supplied by mixing stimulated DMSP production in the prymnesiophyte-dominated assemblage, a response similar to that generally observed during the first days of most of the large-scale ocean iron fertilizations (OIFs). These results suggest that the stimulation of DMSP production takes place whatever the Fe supply mode: atmospheric dust deposition, as simulated by OIFs, or mixing, as reported in this study.©2010 American Society of Limnology and Oceanography, Inc.

YANG, G.-P., M. LEVASSEUR, S. MICHAUD, A. MERZOUK, M. LIZOTTE, M. SCARRATT, 2009. Distribution of dimethylsulfide and dimethylsulfoniopropionate and its relation with phytoneuston in the surface microlayer of the western North Atlantic during summer. Biogeochemistry, 94(3): 243-254.

[Résumé disponible seulement en anglais]
One of the key steps towards predicting dimethylsulfide (DMS) emission to the atmosphere is to understand the distribution and cycling of biogenic sulfur in the microlayer. In this study, we examined the distribution of DMS and dissolved and particulate fractions of dimethylsulfoniopropionate (DMSPd and DMSPp) in the surface microlayer and bulk water of the western North Atlantic during July 2003. DMS concentrations in the bulk water varied from 0.71 to 7.65 nM. In contrast, DMS concentrations in the surface microlayer were fairly low (0.17–1.33 nM). Average concentrations of DMSPd and DMSPp in the bulk water were 2.09 (1.87–6.25) and 44.1 (8.06–119.8) nM, respectively, and those in the surface microlayer were 15.4 (4.06–54.3) and 29.9 (7.32–97.0) nM. In general, DMS was depleted in the microlayer (mean concentration: 0.60 nM) relative to the bulk water (mean concentration: 2.38 nM) with enrichment factors (the ratio of the microlayer concentration to bulk water concentration) ranging from 0.13 to 0.54. There was no consistent enrichment of DMSPp and chlorophyll a in the microlayer. On the contrary, DMSPd appeared to be highly enriched in the microlayer with an average EF of 4.89. The concentration of phaeopigments was also generally greater in the microlayer than in the bulk water, presumably due to enhanced photo-oxidation of chlorophyll a under high surface light intensities in the microlayer. In the study area, the concentration of DMSPp was significantly correlated with the abundance of dinoflagellates in the microlayer. Moreover, a significant correlation between the distributions of DMS, DMSPp, chlorophyll a and phaeopigment concentrations in the microlayer and the bulk water demonstrated that the biogenic materials in the microlayer come primarily from the bulk water below.©2009 Springer Science+Business Media B.V.

MERZOUK, A., M. LEVASSEUR, M. SCARRATT, S. MICHAUD, M. LIZOTTE, R.B. RIVKIN, R.P. KIENE, 2008. Bacterial DMSP metabolism during the senescence of the spring diatom bloom in the Northwest Atlantic. Mar. Ecol. Prog. Ser., 369: 1-11.

[Résumé disponible seulement en anglais]
The impact of the decline of the vernal bloom on the bacterial metabolism of dimethylsulfoniopropionate (DMSP), the precursor of dimethylsulfide (DMS), was investigated during a 7 d Lagrangian study conducted in the Northwest Atlantic in spring 2003. Daily variations in bacterial leucine incorporation, dissolved DMSP (DMSPd) uptake and DMS production rates were measured in the surface mixed layer (SML) and in the deep chlorophyll a maximum (DCM) that formed as the bloom collapsed. Seawater samples were amended with 35S-DMSPd, and the products of bacterial DMSPd degradation were measured during 3 h on-board incubations. The gradual decrease in phytoplankton biomass and diatom abundance measured in the SML was accompanied by a sharp doubling of the bacterial abundance and a peak in leucine incorporation rate on Day 2, suggesting that bacteria responded to a transient pulse in dissolved organic matter. Bacterial DMSPd uptake and DMS production were highest on Days 1 and 2 (1.2 and 0.10 nmol l-1 h-1, respectively), but rapidly decreased by Day 3, suggesting that DMSPd was becoming a less important substrate for the growing bacterial assemblage as other substrates became available. Bacterial DMSPd uptake and DMS production rates were also low in the DCM despite very high DMS yields (40 to 50 %), showing that neither the decline of the diatom spring bloom in the SML nor the accumulation of cells in the DCM resulted in a stimulation of bacterial DMSP metabolism or accumulation of DMS. The present study provides new field evidence for the potential uncoupling between bacterial production and DMS dynamics likely due to variations in the availability of other S-containing organic compounds released during the decay of phytoplankton blooms.©2008 Inter-Research

LIZOTTE, M., M. LEVASSEUR, M.G. SCARRATT, S. MICHAUD, A. MERZOUK, M. GOSSELIN, J. POMMIER, 2008. Fate of dimethylsulfoniopropionate (DMSP) during the decline of the northwest Atlantic Ocean spring diatom bloom. Aquat. Microb. Ecol., 52(2): 159-173.

[Résumé disponible seulement en anglais]
A 7 d Lagrangian process study of the biogeochemical cycling of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) was conducted within a decaying diatom bloom in the northwest Atlantic Ocean in spring 2003. Ambient profiles of DMSP and DMS were surveyed daily in the water column and were used to estimate in situ net transformation rates. Phytoplankton and bacterioplankton abundance were determined within the surface mixed layer (SML) as well as at the deep chlorophyll maximum (DCM), and sinking fluxes of particulate DMSP (DMSPp) below 75 to 100 m were assessed using free-drifting particle interceptor traps. Chlorophyll a (chl a) concentration and diatom abundance declined in the SML over the course of the study period, and the phytoplankton chl a biomass progressively settled above the nitracline forming the DCM. The decline of the diatom bloom coincided with the settling of DMSPp out of the SML and the formation of a DMSP-rich layer at the DCM. The low daily sinking loss rate of DMSPp at 75 m (<2 % d-1) provided confirmation of the efficient retention of DMSPp at the DCM. The decaying bloom gave rise to an initial release of dissolved DMSP (DMSPd) in the upper water column, which was rapidly consumed by the growing bacterial community. The rapid loss of DMSPd was accompanied by significant increases in net production of DMS in the SML and fluxes of DMS to the atmosphere. Despite this increase in DMS dynamics, overall in situ net production rates remained fairly low during the 7 d period (≤0.4 nmol DMS l-1 d-1), suggesting that demethylation by the developing bacterial community dominated DMSPd-consuming processes.©2008 Inter-Research

SCARRATT, M.G., M. LEVASSEUR, S. MICHAUD, S. ROY, 2007. DMSP and DMS in the Northwest Atlantic: late-summer distributions, production rates and sea-air fluxes. Aquat. Sci., 69(3): 292-304.

[Résumé disponible seulement en anglais]
DMSP and DMS were measured along a set of transects in the Northwest Atlantic during September, 1999. Six 24 h Lagrangian stations were occupied between 36° and 61° N latitude, covering subtropical to polar water types. Profiles of total DMSP (DMSPt), DMS, chl a, and oceanographic variables were determined at each station. Phytoplankton abundance and species assemblage were determined in surface waters and at the depth of the Chl a maximum in all profiles. Between profile stations, DMSPt and DMS samples were collected by a pump while the vessel was moving. Chl a and DMSPt were most abundant in the northern regions, with very low levels in subtropical waters. There was no direct correlation between DMSP t and Chl a. Maximum DMSPt concentrations reached 203 nM in coastal waters and 112 nM in the open ocean. A strong correlation was observed between DMSPt and the abundance of dinoflagellates (Spearman r=0.91; p <0.0001; n=13) and prymnesiophytes (Spearman r=0.91; p<0.0001; n=13). Cryptophytes also showed a weak but significant correlation (Spearman r=0.58; p=0.039; n=13). The waters around Greenland were the only site dominated by diatoms and their abundance was not correlated with DMSPt concentrations. DMS concentrations were low and fairly uniform, with maximum levels of 4.7 nM in coastal waters and 2.2 nM in the open ocean. DMS fluxes from surface waters were calculated based on observed sea-surface concentrations and wind speeds and showed a strong peak associated with a storm event, although no depletion of DMS resulting from the storm was observed. In situ incubation experiments showed DMSP consumption and DMS production rates to be relatively high, notwithstanding the generally low phytoplankton biomass.©2007 Eawag, Dübendorf

MICHAUD, S., M. LEVASSEUR, G. CANTIN, 2007. Seasonal variations in dimethylsulfoniopropionate and dimethylsulfide concentrations in relation to the plankton community in the St. Lawrence Estuary. Estuar. Coast. Shelf Sci., 71: 741-750.

[Résumé disponible seulement en anglais]
Weekly variations in total dimethylsulfoniopropionate (DMSPt) and dimethylsulfide (DMS) were investigated in relation to the phytoplankton assemblage from spring to fall 1994 at a coastal fixed station in the St. Lawrence Estuary. DMSPt and DMS concentrations showed a strong seasonality and were tightly coupled in time. Maximum concentrations of DMSPt and DMS were observed in July and August, during a period of warm water and low nutrient concentrations. Seasonal maxima of 365.4 nmol l-1 for DMSPt and 14.2 nmol l-1 for DMS in early August coincided with the presence of many phytoplankton species, such as Alexandrium tamarense, Dinophysis acuminata, Gymnodinium sp., Heterocapsa rotundata, Protoperidinium ovatum, Scrippsiella trochoidea, Chrysochromulin sp. (6 μm), Cryptomonas sp. (6 μm), a group of microflagellates smaller than 5 μ (mf < 5), many tintinnids, and Mesodinium rubrum. The abundance of mf &<lt; 5 followed the general trend of DMS concentrations. The temporal occurrence of high P. ovatum abundance and DMSPt concentrations suggests that this heterotrophic dinoflagellate can either synthesize DMSP or acquire it from DMSP-rich prey. The calculated sea-to-air DMS flux reached a maximum of 8.36 μmol 2 d1 on August 1. The estimated annual emission from the St. Lawrence Estuary is 77.2 tons of biogenic sulfur to the atmosphere.© 2007 Elsevier Ltd.

LEVASSEUR, M., M.G. SCARRATT, S. MICHAUD, A. MERZOUK, C.S. WONG, M. ARYCHUK, W. RICHARDSON, R.B. RIVKIN, M. HALE, E. WONG, A. MARCHETTI, H. KIYOSAWA, 2006. DMSP and DMS dynamics during a mesoscale iron fertilization experiment in the Northeast Pacific-Part I: temporal and vertical distributions. Deep-Sea Res., Part II, Top. Stud. Oceanogr., 53: 2353-2369.

[Résumé disponible seulement en anglais]
This paper reports on the influence of the Fe fertilization conducted during the subarctic ecosystem response to iron enrichment study (SERIES) on the distribution of the biogenic sulfur compounds dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in the context of changes in plankton composition. The Fe enrichment resulted in a rapid increase in the abundance of a nanoplankton assemblage dominated by Prymnesiophyceae, Prasinophyceae, small diatoms (<5 μm), heterotrophic dinoflagellates, and zooflagellates. This first assemblage persisted for 8 days before collapsing abruptly due to an increase in microzooplankton herbivory. The abundance of large diatoms started to increase shortly after the initial Fe fertilization but peaked 1-2 days after the crash of the nanoplankton bloom. Inside the Fe patch, particulate DMSP (DMSPp) increased from 100 to 285 nmol L-1 during the nanoplankton bloom, decreased rapidly back to initial level as this bloom collapsed, and remained low during the bloom of large diatoms. Outside the patch, phytoplankton and protists abundance and DMSPp concentrations remained low and relatively stable throughout the experiment. DMS concentrations were elevated at the onset of the experiment outside the patch (maximum of 15.7 nmol L-1 on day 1), increased up to 26.5 nmol L-1 10 days after the enrichment, and decreased to ca. 6 nmol L-1 by the end of the experiment. This large natural pulse in DMS coincided with conditions of high irradiance and decreasing wind speed. Inside the Fe patch, DMS concentrations exhibited the same general pattern, but with distinctive features related to the Fe fertilization. First, DMS concentrations tended to increase more rapidly inside the patch during the initial nanoplankton bloom, leading to DMS concentrations ca. 2 times higher inside the patch than outside on day 6. Second, DMS concentrations became consistently lower inside the patch (often below our limit of quantification of 0.03 nmol L-1) than outside (ca. 6 nmol L-1) during the peak of the diatom bloom. Our results thus confirm the rapid increase in nanoplankton and DMSPp reported during all previous Fe-fertilization experiments. On the other hand, the decrease in DMS concentrations measured inside the Fe patch during SERIES is unique and shows that adding Fe to HNLC waters may not always lead to conditions that could mitigate climate warming.©2006 Elsevier Ltd.

SCARRATT, M.G., A. MARCHETTI, M.S. HALE, R.B. RIVKIN, S. MICHAUD, P. MATTHEWS, M. LEVASSEUR, N. SHERRY, A. MERZOUK, W.K.W. LI, H. KIYOSAWA, 2006. Assessing microbial responses to iron enrichment in the Subarctic Northeast Pacific: Do microcosms reproduce the in situ condition?. Deep-Sea Res., Part II, Top. Stud. Oceanogr., 53: 2182-2200.

[Résumé disponible seulement en anglais]
A microcosm experiment was conducted in the NE Pacific in July 2002 to compare the microbial response between microcosms and the Subarctic Ecosystem Response to Iron-Enrichment Study (SERIES) in situ iron-enrichment experiment. Seawater microcosms (20 L) were incubated aboard ship under natural light using three treatments: (1) low-iron seawater amended with 4 nmol l-1 FeSO4 (+Fe); (2) low-iron seawater amended with 4 nmol l-1 FeSO4 and 86 nmol l-1 GeO2 (+Fe+Ge); (3) seawater collected from the in situ Fe-enriched patch (PW). The +Fe+Ge treatment used germanium to control diatom growth to assess the role of diatoms in dimethylsulfoniopropionate (DMSP) production. The following variables were measured in the microcosms and in situ: chlorophyll a (chl a), nitrate (NO‾3), silicic acid (Si(OH)4), phytoplankton abundance and species identification, bacterial abundance (including estimates of low- and high-DNA bacteria), bacterial production, bacterial specific growth rate, particulate and dissolved DMSP and dimethylsulfide (DMS) concentrations. There was little or no significant difference (ANCOVA) in the response of most variables between the +Fe and PW microcosms, but large differences were observed between both these treatments and the in situ data from the enriched patch. Chl a in all microcosms increased from ambient levels (approx. 0.5-1 μg l-1) to approx. 4.5-6.2 μg l-1 after 11 d incubation, when NO‾3 was fully depleted from all microcosms. During this same period, in situ chl a increased more slowly to a maximum of 2.9 μg l-1 on day 11. Nanophytoplankton and picophytoplankton were more abundant in the microcosms relative to the in situ community, which became dominated by large diatoms. Bacterial abundance was similar in the microcosms and in situ, but bacterial production was significantly higher in the microcosms. While neither DMSPd nor DMS accumulation showed significant differences between the microcosms and in situ, particulate DMSP concentrations increased significantly faster in the +Fe and PW treatments. These differences represent bottle effects resulting from the containment of the microcosms, which suppresses grazing, alters community and food web structure, enhances iron and nutrient regeneration, and isolates the community from physical transport and export processes including sinking. Thus during this experiment, the microcosms were not a good model for the in situ system in terms of the effects of iron on the phytoplankton biomass, nutrient uptake, bacterial dynamics and DMSPp production. In the germanium-amended treatment, the inhibition of diatom growth resulted in enhanced growth of other taxa and a suppression of bacterial production, leading to increased production of DMSP and DMS and strong correlations between DMSP, DMS and non-diatom phytoplankton taxa. Diatoms did not contribute significantly to particulate DMSP concentrations. Crown Copyright © 2006 Published by Elsevier Ltd.

BOUILLON, R.-C., W.L. MILLER, M. LEVASSEUR, M. SCARRATT, A. MERZOUK, S. MICHAUD, L. ZIOLKOWSKI, 2006. The effect of mesoscale iron enrichment on the marine photochemistry of dimethylsulfide in the NE subarctic Pacific. Deep-Sea Res., Part II, Top. Stud. Oceanogr., 53: 2384-2397.

[Résumé disponible seulement en anglais]
Measurements of underwater light fields and available quantum yield spectra were used to calculate photochemical removal rates of DMS for surface waters of the northeast subarctic Pacific during the SERIES mesoscale iron-fertilization experiment in July 2002. We observed that the UV portion of the solar spectrum was most important in inducing DMS photo-oxidation, and calculated that UV-B accounted for more than 20 % and UV-A for more than 68 % of the total DMS photo-oxidation near the sea surface. Vertically resolved rates showed that most (>90 %) of the DMS photo-oxidation occurs in the upper 15m of the water column. During the study, calculated rates of DMS photo-oxidation, just below the ocean’s surface ranged from 0.34 to 5.9 μmol m-3d-1. As the study progressed, an initial increase in photo-oxidation rates occurred within the iron-enriched patch and this was followed by a dramatic decrease in rates, whereas little change was observed outside the patch. Changes in DMS concentrations and decreases in the photochemical removal efficiency for DMS were the dominant factors explaining the variation in the DMS photo-oxidation rates. The turnover rate constants for DMS photo-oxidation, calculated for the upper mixed layer (UML) of the water column, (0.03-0.25 d-1) were in the range of those previously published and were at times higher than those calculated for biological consumption of DMS during SERIES. Our results suggest that iron fertilization of an oceanic patch in the northeast Pacific Ocean considerably altered the photochemical removal rates and turnover rate constants of DMS.©2006 Elsevier Ltd.

MERZOUK, A., M. LEVASSEUR, M.G. SCARRATT, S. MICHAUD, R.B. RIVKIN, M.S. HALE, R.P. KIENE, N.M. PRICE, W.K.W. LI, 2006. DMSP and DMS dynamics during a mesoscale iron fertilization experiment in the Northeast Pacific-Part II: biological cycling. Deep-Sea Res., Part II, Top. Stud. Oceanogr., 53: 2370-2383.

[Résumé disponible seulement en anglais]
Dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) biological cycling rates were determined during SERIES, a mesoscale iron-fertilization experiment conducted in the high-nutrient low-chlorophyll (HNLC) waters of the northeast subarctic Pacific. The iron fertilization resulted in the rapid development of a nanoplankton assemblage that persisted for 11 days before abruptly crashing. The nanoplankton bloom was followed by a diatom bloom, accompanied by an important increase in bacterial abundance and production. These iron-induced alterations of the plankton assemblage coincided with changes in the size and biological cycling of the DMSP and DMS pools. The initial nanoplankton bloom resulted in increases in particulate DMSP (DMSPp; 77-180 nmol L-1), dissolved DMSP (DMSPd; 1-24 nmol L-1), and biological gross (0.11-0.78 nmol L-1 h-1) and net (0.04-0.74 nmol L-1 h-1) DMS production rates. During the nanoplankton bloom, DMSPd consumption by bacteria exceeded their sulfur demand and the excess sulfur was probably released as DMS, consistent with the high gross DMS production rates observed during that period. The crash of the nanoplankton bloom was marked by the rapid decline of DMSPp, DMSPd, and gross DMS production to their initial values. Following the crash of the nanoplankton bloom, bacterial production and estimated sulfur demand reached transient maxima of 9.3 μCL-1d-1 and 14.2 nmol S L-1d-1, respectively. During this period of high bacterial production, bacterial DMSPd consumption was also very high (6 nmol L-1h-1), but none of the consumed DMSPd was converted into DMS and a net biological DMS consumption was measured. This transient period initiated a rapid decrease in DMS concentrations inside the iron-enriched patch, which persisted during the following diatom bloom due to low biological gross and net DMS production that prevented the replenishment of DMS. Our results show that the impact of Fe fertilization on DMS production in HNLC waters result from a complex interplay between the dynamics of the algal blooms and their influence on bacterial DMSP and DMS metabolism. ©2006 Elsevier Ltd.

LE CLAINCHE, Y., M. LEVASSEUR, A. VÉZINA, R.-C. BOUILLON, A. MERZOUK, S. MICHAUD, M. SCARRATT, C.S. WONG, R.B. RIVKIN, P.W. BOYD, P.J. HARRISON, W.L. MILLER, C.S. LAW, F.J. SAUCIER, 2006. Modeling analysis of the effect of iron enrichment on dimethyl sulfide dynamics in the NE Pacific (SERIES experiment). J. Geophys. Res. (C Oceans), 111, art. no C01011, 15 p.

[Résumé disponible seulement en anglais]
The large-scale iron enrichment conducted in the NE Pacific during the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES) triggered a phytoplankton bloom dominated successively by nanophytoplankton and large diatoms. During the first 14 days, surface dimethyl sulfide (DMS) levels increased both inside (up to 22 nmol L-1) and outside (up to 19 nmol L-1) the patch, with no consistent Fe effect. Later, DMS concentrations became sixfold lower inside the patch than outside. In this study, we used a DMS budget module embedded in a one-dimensional ocean turbulence model to investigate the contribution of the interacting physical, photochemical, and biological processes to this particular DMS response. Temporal variations in biological net DMS production were reconstructed using an inverse modeling approach. Our results show that short-term (days) variations in both the physical processes (i.e., turbulent mixing and ventilation) and the biological cycling of DMS are needed to explain the time evolution of DMS concentrations both outside and inside the Fe-enriched patch. The biological net DMS production was generally high (up to 0.35 nmol L-1 h-1) and comparable outside and inside the patch during the first 10 days, corresponding to the observed accumulation of DMS inside and outside the patch. Later, it became negative (net DMS biological consumption) inside the patch, suggesting a change in dimethylsulfoniopropionate bacterial metabolism. This study stresses the importance of short-term variations in biological processes and their sensitivity to the physical environment in shaping the DMS response to iron enrichment.©2006 American Geophysical Union

YANG, G.-P., M. LEVASSEUR, S. MICHAUD, M. SCARRATT, 2005. Biogeochemistry of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) in the surface microlayer and subsurface water of the western North Atlantic during spring. Mar. Chem., 96(3-4): 315-329.

[Résumé disponible seulement en anglais]
Sixteen surface microlayer samples and corresponding subsurface water samples were collected in the western North Atlantic during April-May 2003 to study the distribution and cycling of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) and the factors influencing them. In the surface microlayer, high concentrations of DMS appeared mostly in the samples containing high levels of chlorophyll a, and a significant correlation was found between DMS and chlorophyll a concentrations. In addition, microlayer DMS concentrations were correlated with microlayer DMSPd (dissolved) concentrations. DMSPd was found to be enriched in the microlayer with an average enrichment factor (EF) of 5.19. However, no microlayer enrichment of DMS was found for most samples collected. Interestingly, the DMS production rates in the microlayer were much higher than those in the subsurface water. Enhanced DMS production in the microlayer was likely due to the higher concentrations of DMSPd in the microlayer. A consistent pattern was observed in this study in which the concentrations of DMS, DMSPd, DMSPp (particulate) and chlorophyll a in the microlayer were closely related to their corresponding subsurface water concentrations, suggesting that these constituents in the microlayer were directly dependent on the transport from the bulk liquid below. Enhanced DMS production in the microlayer further reinforces the conclusion that the surface microlayer has greater biological activity relative to the underlying water.©2005 Elsevier B.V.

MERZOUK, A., M. LEVASSEUR, M. SCARRATT, S. MICHAUD, M. GOSSELIN, 2004. Influence of dinoflagellate diurnal vertical migrations on dimethylsulfoniopropionate and dimethylsulfide distribution and dynamics (St. Lawrence Estuary, Canada). Can. J. Fish. Aquat. Sci., 61: 712-720.

Nous avons étudié l'influence de la migration verticale journalière des dinoflagellés Alexandrium tamarense et Scrippsiella trochoidea sur la dynamique du déméthylsulfoniopropionate (DMSP) et du sulfure de diméthyle (DMS) dans une expérience de type lagrangien de 34 h dans l'estuaire du Saint-Laurent en juillet 2000. Le DMSP particulaire (DMSPp), le DMSP dissous (DMSPd) et le DMS suivent tous des patterns journaliers avec des concentrations minimales durant la nuit et des concentrations maximales vers midi. Les concentrations de DMSPp sont en corrélation avec l'abondance des deux dinoflagellés à migration verticale qui sont riches en DMSP. Le rapport DMSPp:Chl a suit des variations journalières semblables, ce qui indique une néosynthèse de DMSP induite par la lumière durant le jour. Les variations journalières du rapport DMS:Chl a indiquent que l'accumulation de DMS vers midi résulte de réactions physiologiques des algues et (ou) des bactéries à la lumière. La production biologique brute de DMS et la consommation bactérienne de DMS sont déphasées, ce qui entraîne des fluctuations rapides de DMS. Ces résultats démontrent que dans les systèmes dominés par des dinoflagellés riches en DMSP et contenant des DMSP lyases, les concentrations de DMS peuvent varier par un facteur allant jusqu'à 10 au cours d'une période 24 h. On doit tenir compte de ces variations journalières lorsqu'on estime la contribution de tels systèmes au flux de DMS de la mer à l'atmosphère.©2004 NRC Canada

LEVASSEUR, M., M. SCARRATT, S. ROY, D. LAROCHE, S. MICHAUD, G. CANTIN, M. GOSSELIN, A. VÉZINA, 2004. Vertically resolved cycling of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in the Northwest Atlantic in spring. Can. J. Fish. Aquat. Sci., 61: 744-757.

En mai 1998, nous avons mesuré les profils des concentrations ambiantes et des changements nets de diméthylsulfoniopropionate particulaire (DMSPp), de diméthylsulfoniopropionate dissous (DMSPd) et de sulfure de diméthyle (DMS) dans trois provinces biogéographiques du nord-ouest de l'Atlantique, soit le plateau continental (Grands Bancs), la dérive nord-atlantique et la gyre subtropicale de l'Atlantique nord (mer des Sargasses). Toutes les stations/profondeurs affichent d'importantes pertes de DMSPp (jusqu'à 18,0 nmol·L-1·jour-1). Le recyclage du DMSP et du DMS varie en fonction de la composition des communautés planctoniques et de leur stade de développement. Les conditions qui suivent l'efflorescence des diatomées sur les Grands Bancs sont associées à une utilisation efficace du DMSP par le microzooplancton et les bactéries. La production bactérienne de DMS contrebalance la consommation bactérienne de DMS, ce qui explique la faible production nette de DMS (0,3 nmol·L-1·jour-1). La situation est très différente dans les stations de la dérive nord-atlantique et de la mer des Sargasses où les flagellés foisonnent et où la plus grande partie de la perte de DMSPp est récupérée dans le pool de DMSP dissous, ce qui indique que le métabolisme bactérien du DMSP y est moins actif. Dans ces situations, la scission du DMSPd est importante et elle dépasse la consommation bactérienne de DMS, ce qui permet une production nette de DMS (jusqu'à 1,8 nmol·L-1·jour-1). Ces résultats indiquent que la production nette maximale de DMS se produit dans les systèmes d'algues en croissance, dans lesquels la production de DMSPd due au broutage du microzooplancton surpasse les besoins en carbone et en soufre des bactéries.©2004 NRC Canada

LEVASSEUR, M., J.-Y. COUTURE, A.M. WEISE, S. MICHAUD, M. ELBRACHTER, G. SAUVÉ, E. BONNEAU, 2003. Pelagic and epiphytic summer distributions of prorocentrum lima and P. mexicanum at two mussel farms in the Gulf of St.Lawrence, Canada. Aquat. Microbiol. Ecol., 30: 283-293.

MICHAUD, S., M. LEVASSEUR, G. DOUCETTE, G. CANTIN, 2002. Particle size fractionation of paralytic shellfish toxins (PSTs): seasonal distribution and bacterial production in the St. Lawrence estuary, Canada. Toxicon, 40: 1451-1462.

WEISE, A.M., M. LEVASSEUR, F.J. SAUCIER, S. SENNEVILLE, E. BONNEAU, S. ROY, G. SAUVÉ, S. MICHAUD, J. FAUCHOT, 2002. The link between precipitation, river runoff, and blooms of the toxic dinoflagellate Alexandrium tamarense in the St. Lawrence. Can. J. Fish. Aquat. Sci., 59: 464-473.

Les floraisons du dinoflagellé toxique Alexandrium tamarense, responsable de l'intoxication paralysante par les mollusques, sont des événements annuels récurrents dans l'estuaire et le golfe du Saint-Laurent, Québec, Canada. L'analyse des données d'abondances de A. tamarense entre 1989 et 1998 à Sept-Îles, un site présumé d'initiation des floraisons dans le nord-ouest du golfe du Saint-Laurent, montre que l'initiation, la durée et l'ampleur des floraisons toxiques de A. tamarense varient d'une année à l'autre. Les données hydrologiques et météorologiques indiquent que les précipitations, le débit de la rivière Moisie et le vent sont étroitement liés au patron annuel de floraison. Les 10 années de résultats démontrent que dans ce système : (i) un débit élevé de la rivière Moisie dû à une importante crue printanière ou à de fortes précipitations durant l'été et l'automne peut déclencher des floraisons de A. tamarense, (ii) un débit élevé de la rivière Moisie combiné à une période de vents faibles (< 4 m times s-1) favorise le développement continu des floraisons et (iii) des vents > 8 m times s-1 dispersent et mettent fin aux floraisons. La salinité, qui reflète l'état général de la colonne d'eau en termes d'apport d'eau douce et de stabilité, démontre une forte corrélation négative avec la probabilité d'observer des cellules de A. tamarense à cette saison. Ce paramètre pourrait donc être utilisé comme outil pour prédire la présence de A. tamarense dans ce système.

SCARRATT, M.G., M. LEVASSEUR, S. MICHAUD, G. CANTIN, M. GOSSELIN, S.J. DE MORA, 2002. Influence of phytoplankton taxonomic profile on the distribution of dimethylsulfide and dimethylsulfoniopropionate in the northwest Atlantic. Mar. Ecol. Prog. Ser., 244: 49-61.

COUTURE, J.Y., M. LEVASSEUR, E. BONNEAU, C. DESJARDINS, G. SAUVÉ, S.S. BATES, C. LÉGER, R. GAGNON, S. MICHAUD, 2001. Spatial and temporal variation of domoic acid in molluscs and of Pseudo-nitzschia spp. blooms in the St. Lawrence from 1998 to 2000. Can. Tech. Rep. Fish. Aquat. Sci., 2375, 24 p.

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La présence dans les mollusques de l'acide domoïque (toxine responsable de l'intoxication amnestique par les mollusques - IAM) est suivie dans l'estuaire et le nord du golfe du Saint-Laurent depuis 1997 par l'Agence canadienne d'inspection des aliments (ACIA). Les résultats indiquent une évolution spatiale et temporelle de la contamination par l'acide domoïque au cours des années 1998 à 2000. Des traces de cette toxine ont d'abord été détectées dans des gonades de pétoncles géants pêchés au large des Îles-de-la-Madeleine a l'été 1998. En 1999, les concentrations d'acide domoîque dans les glandes digestives de pétoncles géants du même secteur atteignaient 585 ug g-1, bien que les muscles adducteurs n'étaient pas contaminés. Pendant la même période, des teneurs de près de 25 ug g-1 de glande digestive étaient mesurées dans des pétoncles géants récoltés dans la lagune de Havre-aux-Maisons, alors que des concentrations traces étaient mesurées pour la première fois dans des myes communes récoltées sur la Basse Côte-Nord. En 2000, les glandes digestives des pétoncles géants des Îles-de-la-Madeleine demeuraient intoxiquées et des traces d'acide domoïque étaient mesurées dans des myes communes, moules bleues et couteaux de mer tout le long de la Côte-Nord du Saint-Laurent, de Tadoussac à Havre-Saint-Pierre. Conjointement aux données de l'inspection, le programme de monitorage des algues nuisibles de l'Institut Maurice-Lamontagne (Pêches et Océans Canada) a révélé la présence de deux espèces de diatomées potentiellement productrices d'acide domoïque dans le Saint-Laurent: Pseudo-nitzschia seriata et Pseudo-nitzschia delicatissima. L'examen des données a mis en évidence une coïncidence entre l'apparition de l'acide domoïque dans certains mollusques des Îles-de-la-Madeleine et de la Côte-Nord et la présence de P. seriata alors que des floraisons massives de P. delicatissima (en l'absence de P. seriata) n'occasionnent pas de toxicité. Les analyses en laboratoire réalisées sur une souche de P. seriata isolée de l'estuaire du Saint-Laurent lors d'un épisode de toxicité ont montré sa capacité à produire de l'acide domoïque alors que toutes les tentatives faites en ce sens avec P. delicatissima isolé d'autres régions de l'est du Canada se sont avérées négatives jusqu'à maintenant. Ces résultats récents indiquent que les floraisons de P. seriata dans le Saint-Laurent et les intoxications des mollusques par l'acide domoïque qui en résultent représentent un risque potentiel qui devra être considéré dans l'avenir.

LEVASSEUR, M., J.-Y. COUTURE, G. SAUVÉ, S. MICHAUD, 2001. Contamination des mollusques du Québec par les phycotoxines diarrhéiques (DSP) et amnestiques (ASP) et recherche des sources potentielles de phycotoxines DSP. Rapp. tech. can. sci. halieut. aquat., 2350, 41 p.

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Cette étude fait suite à la détection pour la première fois de phycotoxines DSP et ASP dans des mollusques moules et pétoncles) aux Îles-de-la-Madeleine lors de l'été 1998. Nos objectifs étaient 1) de déterminer si la microalgue Prorocentrum lima pouvait être responsable de la présence de DSP dans les moules d'élevage des Îles-de-la-Madeleine et 2) d'évaluer l'étendue de la contamination des mollusques par le DSP et l'ASP dans d'autres régions du Québec. Notre échantillonnage réalisé dans deux sites mytilicoles des Îles-de-la-Madeleine a mis en évidence la présence régulière de P. lima attaché aux épibiontes se développant sur les boudins de culture de moules. P. lima se retrouvait fréquemment dans les glandes digestives des moules mais apparemment en trop faibles concentrations pour les rendre toxiques lors de notre étude. Dans les autres régions du Québec, 9,5 % des 252 mollusques analysés (principalement des moules) présentaient de faibles concentrations de DTX, le maximum atteint étant de 0,4 mug/g de glande digestive. L'échantillonnage réalisée aux Îles-de-la-Madeleine a également permis d'identifier pour la première fois dans le Saint-Laurent une autre microalgue toxique: Prorocentrum mexicanum, P. mexicanum est connu pour produire des toxines de type DSP, mais différentes que celles produites par P. lima. Ces toxines n'ont pas été mesurées lors de cette étude mais elles pourraient représenter un risque qui devra être évalué ultérieurement. Finalement, des concentrations importantes d'ASP (jusqu'à 550 mug/g) ont été mesurées dans les glandes digestives de pétoncles provenant des Îles-de-la-Madeleine. La source de ces toxines et l'importance des contaminations restent à définir.

COUTURE, J.Y., M. LEVASSEUR, E. BONNEAU, C. DESJARDINS, G. SAUVÉ, S.S. BATES, C. LÉGER, R. GAGNON, S. MICHAUD, 2001. Variations spatiales et temporelles des concentrations d'acide domoïque dans les mollusques et des abondances de Pseudo-nitzschia spp. dans le Saint-Laurent de 1998 à 2000. Rapp. tech. can. sci. halieut. aquat., 2375, 25 p.

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La présence dans les mollusques de l'acide domoïque (toxine responsable de l'intoxication amnestique par les mollusques - IAM) est suivie dans l'estuaire et le nord du golfe du Saint-Laurent depuis 1997 par l'Agence canadienne d'inspection des aliments (ACIA). Les résultats indiquent une évolution spatiale et temporelle de la contamination par l'acide domoïque au cours des années 1998 à 2000. Des traces de cette toxine ont d'abord été détectées dans des gonades de pétoncles géants pêchés au large des Îles-de-la-Madeleine a l'été 1998. En 1999, les concentrations d'acide domoîque dans les glandes digestives de pétoncles géants du même secteur atteignaient 585 ug g-1, bien que les muscles adducteurs n'étaient pas contaminés. Pendant la même période, des teneurs de près de 25 ug g-1 de glande digestive étaient mesurées dans des pétoncles géants récoltés dans la lagune de Havre-aux-Maisons, alors que des concentrations traces étaient mesurées pour la première fois dans des myes communes récoltées sur la Basse Côte-Nord. En 2000, les glandes digestives des pétoncles géants des Îles-de-la-Madeleine demeuraient intoxiquées et des traces d'acide domoïque étaient mesurées dans des myes communes, moules bleues et couteaux de mer tout le long de la Côte-Nord du Saint-Laurent, de Tadoussac à Havre-Saint-Pierre. Conjointement aux données de l'inspection, le programme de monitorage des algues nuisibles de l'Institut Maurice-Lamontagne (Pêches et Océans Canada) a révélé la présence de deux espèces de diatomées potentiellement productrices d'acide domoïque dans le Saint-Laurent: Pseudo-nitzschia seriata et Pseudo-nitzschia delicatissima. L'examen des données a mis en évidence une coïncidence entre l'apparition de l'acide domoïque dans certains mollusques des Îles-de-la-Madeleine et de la Côte-Nord et la présence de P. seriata alors que des floraisons massives de P. delicatissima (en l'absence de P. seriata) n'occasionnent pas de toxicité. Les analyses en laboratoire réalisées sur une souche de P. seriata isolée de l'estuaire du Saint-Laurent lors d'un épisode de toxicité ont montré sa capacité à produire de l'acide domoïque alors que toutes les tentatives faites en ce sens avec P. delicatissima isolé d'autres régions de l'est du Canada se sont avérées négatives jusqu'à maintenant. Ces résultats récents indiquent que les floraisons de P. seriata dans le Saint-Laurent et les intoxications des mollusques par l'acide domoïque qui en résultent représentent un risque potentiel qui devra être considéré dans l'avenir.

SCARRATT, M., G. CANTIN, M. LEVASSEUR, S. MICHAUD, 2000. Particle size-fractionated kinetics of DMS production : where does DMSP cleavage occur at the microscale?. J. Sea Res., 43(3-4): 245-252.

SCARRATT, M.G., M. LEVASSEUR, S. SCHULTES, S. MICHAUD, G. CANTIN, A. VÉZINA, M. GOSSELIN, S.J. DE MORA, 2000. Production and consumption of dimethylsulfide (DMS) in North Atlantic waters. Mar. Ecol. Prog. Ser., 204: 13-26.

SCHULTES, S., M. LEVASSEUR, S. MICHAUD, G. CANTIN, G. WOLFE, M. GOSSELIN, S. DE MORA, 2000. Dynamics of dimethylsulfide production from dissolved dimethylsulfoniopropionate in the Labrador Sea. Mar. Ecol. Prog. Ser., 202: 27-40.

WOLFE, G.V., M. LEVASSEUR, G. CANTIN, S. MICHAUD, 2000. DMSP and DMS dynamics and microzooplankton grazing in the Labrador Sea : application of the dilution technique. Deep-Sea Res., Part I, 47: 2243-2264.

WOLFE, G.V., M. LEVASSEUR, G. CANTIN, S. MICHAUD, 1999. Microbial consumption and production of dimethyl sulfide (DMS) in the Labrador Sea. Aquat. Microbiol. Ecol., 18: 197-205.

CANTIN, G., M. LEVASSEUR, S. SCHULTES, S. MICHAUD, 1999. Dimethylsulfide (DMS) production by size-fractionated particles in the Labrador Sea. Aquat. Microbiol. Ecol., 19: 307-312.

DESBIENS, M., J. ROY, S. MICHAUD, M. LEVASSEUR, 1998. Absence de biotoxines PSP dans les gonades d'oursins. MAPAQ, DIT, Doc. rech., 98/07, 5 p.

SAKKA, A., M. GOSSELIN, M. LEVASSEUR, S. MICHAUD, P. MONFORT, S. DEMERS, 1997. Effect of ultraviolet radiation on the marine production of dimethylsufoniopropionate and. Mar. Ecol. Prog. Ser., 149(1-3): 227-238.

LEVASSEUR, M., S. SHARMA, G. CANTIN, S. MICHAUD, M. GOSSELIN, L. BARRIE, 1997. Biogenic sulfur emissions from the Gulf of Saint Lawrence and assessment of its impact on the Canadian east coast. J. Geophys. Res. (D Atmospheres), 102(D23): 28025-28039.

CASTONGUAY, M., M. LEVASSEUR, J.-L. BEAULIEU, F. GRÉGOIRE, S. MICHAUD, E. BONNEAU, S.S. BATES, 1997. Accumulation of PSP toxins in Atlantic mackerel : seasonal and ontogenic variations. J. Fish Biol., 50: 1203-1213.

CANTIN, G., M. LEVASSEUR, M. GOSSELIN, S. MICHAUD, 1996. Role of zooplankton in the mesoscale distribution of surface dimethylsulfide concentrations in the Gulf of St. Lawrence, Canada. Mar. Ecol. Prog. Ser., 141: 103-117.

LEVASSEUR, M., S. MICHAUD, J. EGGE, G. CANTIN, J.C. NEJSTGAARD, R. SANDERS, E. FERNANDEZ, P.T. SOLBERG, B. HEIMDAL, M. GOSSELIN, 1996. Production of DMSP and DMS during a mesocosm study of an Emiliania huxleyi bloom : influence of bacteria and Calanus finmarchicus grazing. Mar. Biol., 126: 609-618.

BEAULIEU, J.-L., M. CASTONGUAY, M. LEVASSEUR, F. GRÉGOIRE, S. MICHAUD, E. BONNEAU, S.S. BATES, 1996. Rôle des toxines IPM (intoxication paralysante par les mollusques) dans une mortalité de maquereau bleu (Scomber scombrus) en Nouvelle-Écosse en 1993 ; Role of PSP (Paralytic Shellfish Poisoning) toxins in an Atlantic mackerel (Scomber scombrus) mortality in Nova Scotia in 1993. Rapp. can. ind. sci. halieut. aquat. ; Can. Ind. Rep. Fish. Aquat. Sci., 236, 17 p.

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Une mortalité de maquereau bleu (Scomber scombrus) en mai 1993 au Cap Breton (N. É.) nous a incités à déterminer si les toxines IPM (intoxication paralysante par les mollusques) pouvaient en être responsables. Les toxines sont des toxines naturelles produites par des algues microscopiques appelées phytoplancton. Au moment de la mortalité, l'eau de mer et les estomacs de maquereaux morts ne contenaient pas de phytoplancton toxique et aucune toxine IPM n'a été détectée dans les chairs de maquereau. Les sept maquereaux morts trouvés sur les plages avaient une quantité de toxines IPM dans les foies similaire à celle de 57 maquereaux vivant pêchés dans la même région en même temps. De plus, la quantité de toxines du foie était la même pour des maquereaux morts et vivants provenant de trappes de la même région. L'ensemble de ces résultats indique qu'il est peu probable que les toxines IPM du foie aient été responsables de la mortalité. Nous avons réalisé un échantillonnage additionnel de maquereaux provenant de la pêche commerciale du sud et du nord du Golfe de juin à octobre 1993. La quantité totale de toxines IPM par foie augmente graduellement avec l'âge et la longueur du poisson. Ces résultats démontrent que le maquereau bioaccumule progressivement les toxines IPM dans le foie au cours de sa vie. La quantité de toxines du foie augmente aussi pendant l'été montrant que le maquereau accumule des toxines pendant son séjour estival dans le golfe du St-Laurent. En accumulant ainsi des toxines, le maquereau peut devenir une proie létale pour ses prédateurs naturels. Il ne pose cependant aucun danger pour l'homme en autant que les viscères ne sont pas consommés.

GOSSELIN, M., M. LEVASSEUR, N. SIMARD, S. MICHAUD, S. SHARMA, P. BRICKELL, T. BATES, 1996. Contribution of planktonic and ice algae to dimethylsulfide production across the Arctic ocean in Summer. Pages 42-44 in W. Tucker, D. Cate & V. Keating (ed.). The 1994 Arctic Ocean Section : the first major scientific crossing of the Arctic Ocean. U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H. (Special report, 96-23).

BRATBAK, G., M. LEVASSEUR, S. MICHAUD, G. CANTIN, E. FERNANDEZ, B.R. HEIMDAL, M. HELDAL, 1995. Viral activity in relation to Emiliania huxleyi blooms : a mechanism of DMSP release. Mar. Ecol. Prog. Ser., 128: 133-142.

LEVASSEUR, M., T. GAMACHE, I. ST-PIERRE, S. MICHAUD, 1995. Does the cost of NO3- reduction affect the production of harmful compounds by Alexandrium excavatum?. Pages 463-468 Harmful Marine Algal Blooms : proceedings of the Sixth International Conference on Toxic Marine Phytoplankton, October 1993, Nantes, France. Lavoisier, Paris and Intercept Ltd, Andover, England.

LEVASSEUR, M., M. GOSSELIN, S. MICHAUD, 1994. A new source of dimethylsulfide (DMS) for the arctic atmosphere : ice diatoms. Mar. Biol., 121: 381-387.

LAYCOCK, M.V., S.W. AYER, M. BILODEAU, J.-P. GAGNÉ, S. HSIAO, J.F. JELLETT, A. LAWRENCE, M. LEDOUX, P. MASSELIN, D. McLACHLAN, S. MICHAUD, S.K. MOHAPATRA, K. SOHET, I. ST-PIERRE, K. THOMAS, B.M. TWAROG, 1992. Detection and quantification of toxic algae and toxins. Pages 81-90 in J.-C. Therriault & M. Levasseur (ed.). Proceedings of the Third Canadian Workshop on Harmful Marine Algae, Maurice-Lamontagne lnstitute, Mont-Joli, Québec, 12-14 May, 1992 .

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