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Bibliography of the Maurice Lamontagne Institute

Maurice LEVASSEUR

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 .

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 .

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 .

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.

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 .

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.

GAGNON, R., M. LEVASSEUR, A.M. WEISE, J. FAUCHOT, P.G.C. CAMPBELL, B.J. WEISSENBOECK, A. MERZOUK, M. GOSSELIN, B. VIGNEAULT, 2005. Growth stimulation of Alexandrium tamarense (dinophyceae) by humic substances from the Manicouagan River (eastern Canada). J. Phycol., 41(3): 489-497 .

In the St. Lawrence Estuary, annual recurrent blooms of the toxic dinoflagellate Alexandrium tamarense L. Balech are associated with brackish waters. Riverine inputs are suspected to favor bloom development by increasing water column stability and/or by providing growth stimulants such as humic substances (HS). A 17-day culture experiment was conducted to evaluate the importance of HS as growth factors for A. tamarense. Nonaxenic cultures were exposed to four HS extracts from three different sources: humic and fulvic acids isolated from the Manicouagan River, Quebec, Canada; humic acids from the Suwannee River, Georgia, United States; and a desalted alkaline soil extract. For each extract, four concentrations were tested as supplements to the artificial Keller medium, a nitrate-rich algal culture medium. Additions of HS from all sources significantly enhanced the overall growth rates relative to the controls. Concentrations of HS, estimated by UV spectrophotometry, remained constant throughout the exponential growth phase, suggesting that the HS were acting mainly as growth promoters during our experiment. Dose-response curves indicated that HS could increase the growth rate of A. tamarense even at low concentrations, such as those encountered in the St. Lawrence Estuary. Our results support the hypothesis that HS from the Manicouagan River plume can stimulate the development of toxic dinoflagellate blooms.©2005 Phycological Society of America

LEVASSEUR, M., 2004. Environmental Chemistry of DMS(P) and Related Compounds [Troisième symposium international sur la biochimie et la chimie environnementale du DMS(P) et des composés apparentés]. Can. J. Fish. Aquat. Sci., 61: v-vi .

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 .

In May 1998, profiles of ambient concentration and net changes of particulate dimethylsulfoniopropionate (DMSPp), dissolved dimethylsulfoniopropionate (DMSPd), and dimethylsulfide (DMS) were measured in three bio geographic provinces of the Northwest Atlantic: Northwest Atlantic Continental Shelf (Grand Banks), North Atlantic Drift, and North Atlantic Subtropical Gyre (Sargasso Sea). All stations/depths exhibited large losses of DMSPp (up to 18.0 nmol·L-1·day-1). DMSP and DMS cycling varied in relation to the type and development stage of the plankton assemblages. The postdiatom bloom conditions on the Grand Banks were associated with an efficient utilization of DMSP by microzooplankton and bacteria. Bacterial DMS production balanced the DMS bacterial consumption, resulting in little net DMS production (0.3 nmol·L-1·day-1). This contrasted with the North Atlantic Drift and Sargasso Sea stations where flagellates were thriving and most of the DMSPp loss was recovered in the dissolved pool, indicating a less active microbial DMSP metabolism. DMSPd cleavage was high in these latter cases and exceeded DMS bacterial consumption, allowing a net production of DMS (up to 1.8 nmol·L-1·day-1). These results indicate that maximum DMS net production occurs in growing algal systems where the production of DMSPd resulting from microzooplankton grazing exceeds the bacterial requirement in carbon and sulfur.©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 .

FOUILLAND, E., M. GOSSELIN, B. MOSTAJIR, M. LEVASSSEUR, J.-P. CHANUT, S. DEMERS, S. DE MORA, 2003. Effects of ultraviolet-B radiation and vertical mixing on nitrogen uptake by a natural planktonic community shifting from nitrate to silicic acid deficiency. Limnol. Oceanogr., 48(1): 18-30 .

LEE, P.A., P.A. SAUNDER, S.J. DE MORA, D. DEIBEL, M. LEVASSEUR, 2003. Influence of copepod grazing on concentrations of dissolved dimethylsulfoxide and related sulfur compounds in the North Water, Northern Baffin Bay. Mar. Ecol. Prog. Ser., 255: 235-248 .

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 .

LEFÈVRE, M., A. VÉZINA, M. LEVASSEUR, J.W.H. DACEY, 2002. A model of dimethylsulfide dynamics for the subtropical North Atlantic. Deep-Sea Res., Part I, Oceanogr. Res. Pap., 49(12): 2221-2239 .

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 .

Blooms of the toxic dinoflagellate Alexandrium tamarense, which is responsible for paralytic shellfish poisoning, are annually recurrent events in the Estuary and Gulf of St. Lawrence, Quebec, Canada. The analysis of abundance data for this algal species between 1989 and 1998 at Sept-Iles, a presumed initiation site in the north-western Gulf of St. Lawrence, revealed yearly fluctuations in the onset, duration, and magnitude of toxic A. tamarense blooms. Hydrological and meteorological data for the region indicate that rainfall, Moisie River runoff, and wind are highly related to the pattern of bloom development each year. Results from the 10-year data set reveal that in this system: 1) high Moisie River runoff from a prolonged spring freshet or from heavy rainfall events in the summer and fall can initiate A. tamarense blooms; 2) high Moisie River runoff combined with prolonged periods of weak winds (<  4 m times s-1) favour the continued development of blooms; and 3) winds > 8 m times s-1 disrupt blooms. Salinity, which reflects the general state of the water column in terms of freshwater input and stability, had a strong negative correlation with the probability of observing A. tamarense cells at this station and could thus be used as a predictive tool for the presence of cells in this system.

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 .

BOUILLON, R.-C., P.A. LEE, S.J. DE MORA, M. LEVASSEUR, C. LOVEJOY, 2002. Vernal distribution of dimethylsulphide, dimethylsulphoniopropionate, and dimethylsulphoxide in the North Water in 1998. Deep-Sea Res., Part II, 49: 5171-5189 .

BONNEAU, E., J.-Y. COUTURE, M. LEVASSEUR, 2002. Le programme de monitorage des algues toxiques de la région du Québec: un outil précieux pour le développement des connaissances. AZMP Bull. PMZA, 2: 24-25 .

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The Toxic Algae Monitoring Program (TAMP) of the Quebec Region covers the entire maritime area of the Gulf of St. Lawrence, with a network of 11 coastal stations sampled between May and October over the last 13 years. The primary objective of this program is to provide complementary information for the biotoxin monitoring program on shellfish that is carried out each year by the Canadien Food Inspection Agency. TAMP provides identification and counts of toxic algae and also allows the acquisition of new knowledge of new on the dynamics of these algae and on the environmental conditions that favour their growth and development. In this context, the living material and/or the data that have been obtained via TAMP have been used for many other research projects that have already produced several scientific publications. This mutually beneficial relationship between monitoring and research activities has demonstrated a great scientific efficiency and we hope that this approach will be exploited to its full potential in the future. For the Atlantic Zone Monitoring Program of the Quebec Region, TAMP represents an essential association to allow the acquisition of environmental information in the near-shore zone.

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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This study was initiated following the detection for the first time of DSP and ASP phycotoxins in shellfish (blue mussel and scallop) from the Magdalen Islands during the summer of 1998. Our objectives were 1) to determine if Prorocentrum lima may be the source of DSP in cultured mussels from the Magdalen Islands and 2) to evaluate the extent of the contamination by DSP and ASP of molluscs from different areas in Quebec. Our sampling, carried out at two cultured mussel sites in the Magdalen Islands, revealed the regular presence of P. lima fixed on the epibionts growing on the mussel socks. P. lima was frequently found in the digestive glands of the mussels, but apparently in concentrations too low to cause contamination during our study. In other regions of Quebec, 9.5 % of the 252 shellfish analysed (mostly mussels) showed low levels of DTX with a maximum of 0.4 mug/g in the digestive gland. During the sampling conducted in the Magdalen Islands, we also identified, for the first time in Eastern Canada, another toxic microalga: Prorocentrum mexicanum, P. mexicanum is known to produce DSP-type toxins, but different from those produced by P. lima. These toxins were not measured during our study but could represent a risk that needs to be evaluated. Finally, elevated concentrations of ASP (up to 550 mug/g) were measured in the digestive glands of scallops from the Magdalen Islands. The source of these toxins and the importance of the contamination remain to be determined.

LEE, P.A., S.J. DE MORA, M. GOSSELIN, M. LEVASSEUR, R.C. BOUILLON, C. NOZAIS, C. MICHEL, 2001. Particulate dimethysulfoxide in Artic sea-ice Algal communities : the cryoprotectant hypothesis revisisted. J. Phycol., 37: 488-499 .

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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The presence of domoic acid (the toxin responsilbe for Amnesic Shellfish Poisoning - ASP) in shellfish has been monitored in the estuary and the northern Gulf of St. Lawrence since 1997 by the Canadian Food Inspection Agency (CFIA). The results indicate a spatial and temporal evolution of domoic acid contamination between 1998 and 2000. Trace amounts of this toxin were first detected in the gonads of sea scallops from fishing areas offshore of the Iles-de-la-Madeleine in the summer of 1998. In 1999, the concentration of domoic acid in the digestive glands of sea scallops from the same area reached 585 ug g -1, whereas the adductor muscles were not contaminated. At the same time, concentrations of domoic acid close to 25 ug g -1 digestive gland were measured in sea scallops from the Havre-aux-Maisons lagoon while trace amounts were measured for the first time in soft-shell clams collected on the Lower North Shore of the Gulf of St. Lawrence. In 2000, the digestive glands of sea scallops from the Iles-de-la-Madeleine remained toxic and trace amounts of domoic acid were measured in shellfish all along the North Shore, from Tadoussac to Havre-Saint-Pierre. In addition to the CFIA data, the Harmful Algae Monitoring Program of the Maurice Lamontagne Institute (Fisheries and Oceans Canada) revealed the presence of two potentially domoic-acid-producing diatoms in the St. Lawrence: Pseudo-nitzschia seriata and Pseudo-nitzschi delicatissima. Analysis of data showed a link between domoic acid in some shellfish from the Iles-de-la-Madeleine and North Shore and the presence of Pseudo-nitzschia seriata. Dense blooms of P. delicatissima (with no P. seriata) did not cause toxicity. Laboratory analyses performed on a P. seriata strain isolated from the St. Lawrence estuary during a toxic event showed the ability of P. seriata to produce domoic acid whereas all attempts made with P. delicatissima from other regions of eastern Canada have so far been negative. These new results show that P. seriata blooms in the St. Lawrence and the resulting shellfish toxicity due to domoic acid represent a potential risk that needs to be considered in the future.

HARVEY, M., M. STARR, M. LEVASSEUR, 2001. L'état du plancton dans l'estuaire maritime et le golfe du Saint-Laurent en 1999. Naturaliste can., 125(1): 68-70 .

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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The presence of domoic acid (the toxin responsilbe for Amnesic Shellfish Poisoning - ASP) in shellfish has been monitored in the estuary and the northern Gulf of St. Lawrence since 1997 by the Canadian Food Inspection Agency (CFIA). The results indicate a spatial and temporal evolution of domoic acid contamination between 1998 and 2000. Trace amounts of this toxin were first detected in the gonads of sea scallops from fishing areas offshore of the Iles-de-la-Madeleine in the summer of 1998. In 1999, the concentration of domoic acid in the digestive glands of sea scallops from the same area reached 585 ug g -1, whereas the adductor muscles were not contaminated. At the same time, concentrations of domoic acid close to 25 ug g -1 digestive gland were measured in sea scallops from the Havre-aux-Maisons lagoon while trace amounts were measured for the first time in soft-shell clams collected on the Lower North Shore of the Gulf of St. Lawrence. In 2000, the digestive glands of sea scallops from the Iles-de-la-Madeleine remained toxic and trace amounts of domoic acid were measured in shellfish all along the North Shore, from Tadoussac to Havre-Saint-Pierre. In addition to the CFIA data, the Harmful Algae Monitoring Program of the Maurice Lamontagne Institute (Fisheries and Oceans Canada) revealed the presence of two potentially domoic-acid-producing diatoms in the St. Lawrence: Pseudo-nitzschia seriata and Pseudo-nitzschi delicatissima. Analysis of data showed a link between domoic acid in some shellfish from the Iles-de-la-Madeleine and North Shore and the presence of Pseudo-nitzschia seriata. Dense blooms of P. delicatissima (with no P. seriata) did not cause toxicity. Laboratory analyses performed on a P. seriata strain isolated from the St. Lawrence estuary during a toxic event showed the ability of P. seriata to produce domoic acid whereas all attempts made with P. delicatissima from other regions of eastern Canada have so far been negative. These new results show that P. seriata blooms in the St. Lawrence and the resulting shellfish toxicity due to domoic acid represent a potential risk that needs to be considered in the future.

LEVASSEUR, M., A. WEISE, F. SAUCIER, 2001. Potential sensitivity of harmful algal blooms to climate changes. Pages 15-16 in Report of the ICES/IOC Working Group on Harmful Algal Bloom Dynamics. Dublin, Ireland, 12-16 March 2001 (ICES C.M., 2001/C:04) .

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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 .

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 .

FAUCHOT, J., M. GOSSELIN, M. LEVASSEUR, B. MOSTAJIR, C. BELZILE, S. DEMERS, S. ROY, P.Z. VILLEGAS, 2000. Influence of UV-B radiation on nitrogen utilization by a natural assemblage of phytoplankton. J. Phycol., 36: 484-496 .

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 .

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 .

MOUSSEAU, L., M. GOSSELIN, M. LEVASSEUR, S. DEMERS, J. FAUCHOT, S. ROY, P.Z. VILLEGAS, B. MOSTAJIR, 2000. Effects of ultraviolet-B radiation on simultaneous carbon and nitrogen transport rates by estuarine phytoplankton during a week-long mesocosm study. Mar. Ecol. Prog. Ser., 199: 69-81 .

MONTFORT, P., S. DEMERS, M. LEVASSEUR, 2000. Bacterial dynamics in first year sea ice and underlying seawater of Saroma-ko Lagoon (Sea of Okhotsk, Japan) and Resolute Passage (High Canadian Arctic): Inhibitory effects of ice algae on bacterial dynamics. Can. J. Microb., 46: 623-632 .

The seasonal development of bacterial abundance in first year bottom ice and underlying seawater were studied at Saroma-ko Lagoon in Hokkaido, Japan, and at Resolute Passage in the High Canadian Arctic during the algal bloom in spring 1992. The aim of this study was to evaluate whether the high algal concentrations reached during the bloom of ice algae have inhibitory effects on bacterial dynamics. Bacterial abundance (measured as total cell count and colony-forming units CFU) increased with the increase of the algal biomass up to 500 mu g Chla.L-1 in both locations. Culturable fraction (measured as the percentage of CFU counts versus the total cell counts) was between 7 % and 22 % at Saroma-ko, and approximately 0.08 % at Resolute Passage. When algal biomass exceeded 500 mu g of Chla.L-1, both bacterial abundance and culturable fraction decreased significantly. There was a maximum threshold of algal biomass (between 500 and 800 mu g of Chla.L-1) after which bacterial dynamics become negatively coupled to the algal biomass. These results suggest that bactericidal and/or bacteriostatic compounds from these extremely high algal concentrations could explain the decrease in bacterial abundance and culturability in bottom ice observed after the ice algae bloom.

LAROCHE, D., VEZINA, A.F., LEVASSEUR, M., GOSSELIN, M., STEFELS, J., KELLER, M.D., MATRAI, P.A., R.L.J. KWINT, 1999. DMSP synthesis and exudation in phytoplankton : A modeling approach. Mar. Ecol. Prog. Ser., 180: 37-49 .

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 .

MOSTAJIR, B., S. DEMERS, S. DE MORA, C. BELZILE, J.-P. CHANUT, M. GOSSELIN, S. ROY, P.Z. VILLEGAS, J. FAUCHOT, J. BOUCHARD, D. BIRD, P. MONFORT, M. LEVASSEUR, 1999. Experimental test of the effect of ultraviolet-B radiation in a planktonic community. Limnol. Oceanogr., 44: 586-596 .

MOSTAJIR, B., T. SIME-NGANDO, S. DEMERS, C. BELZILE, S. ROY, M. GOSSELIN, J.-P. CHANUT, S. DE MORA, J. FAUCHOT, F. VIDUSSI, M. LEVASSEUR, 1999. Ecological implications of changes in cell size and photosynthetic capacity of marine Prymnesiophyceae induced by ultraviolet-B radiation. Mar. Ecol. Prog. Ser., 187: 89-100 .

KETTLE, A.J., 31 CO-AUTEURS INCLUANT M. LEVASSEUR, 1999. A global database of sea surface dimethylsulfide (DMS) measurements and a procedure to predict sea surface DMS as a function of latitude, longitude, and month. Global Biogeochem. Cycles., 13: 399-444 .

SHARMA, S., L.A. BARRIE, D. PLUMMER, P.C. BRICKELL, M. LEVASSEUR, M. GOSSELIN, T.S. BATES, 1999. Flux estimation of oceanic dimethyl sulfide around north America. J. Geophys. Res. (D Atmospheres), 104(D17): 21327-21342 .

LEE, P.A., S. DE MORA, M. LEVASSEUR, 1999. A review of dimethylsulfoxide in aquatic environments.. Atmos.-Ocean, 37: 439-456 .

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 .

BLASCO, D., M. LEVASSEUR, R. GÉLINAS, R. LAROCQUE, A.D. CEMBELLA, B. HUPPERTZ, E. BONNEAU, 1998. Monitorage du phytoplancton toxique et des toxines de type IPM dans les mollusques du Saint-Laurent : 1989 à 1994. Rapp. stat. can. hydrogr. sci. océan., 151, 117 p .

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The Department of Fisheries and Oceans has conducted monitoring programs for paralytic shellfish poisoning (PSP) and harmful algae in the St. Lawrence since 1984 and 1989, respectively. Harmful algae are sampled weekly at 11 coastal stations from April to November while shellfish are collected at approximately 85 stations from March to November. The most important harmful algae enumerated are Alexandrium tamarense (= Gonyaulax tamarensis), A. ostenfeldii, Dinophysis acuminata, D. norvegica, and Phalacroma rotundatum. The main shellfish species collected are blue mussels (Mytilus edulis) and soft-shelled clams (Mya arenaria). This report presents a synthesis of the data collected between 1984 and 1994 during these monitoring programs. Shellfish generally become toxic)<80 µg STX eq/100 g meat) as soon as the abundance of Alexandrium spp. (A. tamarense + A. ostenfeldii) reaches 1 000 cells L-1. As previously observed in other regions, mussels are generally 5 times more toxic than soft-shelled clams at the same location. Maximum Alexandrium spp. concentrations and PSP toxins in mussels and soft-shelled clams were measured in the upper North Shore, lower St. Lawrence-north Gaspésie, and southeast Gaspésie regions. Very low concentrations of Alexandrium spp. were measured in the lower North Shore and Magdalen Islands regions, where shellfish toxicity has always been below the critical limit of 80 µg STX ea/100 g meat. Alexandrium spp. was also found in low numbers in the southwest Gaspésie region, although mussel toxicité reached values higher than 80 µg STX eq/100 g meat on a few occasions between 1989 adn 1994. The mid-North Shore region is characterized by a gradual east-west increase in Alexandrium spp. abundance and shellfish toxicity. Shellfish collected in the western part of this region often exibit toxicity values higher than 80 µg STX eq/100 g meat. No statistically significant interannual variations in Alexandrium spp. abundance was observed between 1989 and 1994 at our sampling stations. However, we did observed significant interannual variations in mussel toxicity between 1984 and 1994, with minimum and maximum toxicity being recorded in 1987-88 and 1991, respectively.

LEVASSEUR, M., L. BÉRARD-THERRIAULT, E. BONNEAU, S. ROY, 1998. Distribution of the toxic dinoflagellate Alexandrium ostenfeldii in the Gulf of St. Lawrence, Canada. Pages 54-57 in B. Reguera, J. Blanco, M.L. Fernandez & T. Wyatt (ed.). Harmful algae. Xunta de Galacia and Intergovernmental Oceanographic Commission of UNESCO .

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 .

DEMERS, S., C. BELZILE, C., S.R.S. LEAN, B. MOSTAJIR, S. ROY, S. DE MORA, D. BIRD, M. GOSSELIN, J.-P. CHANUT, M. LEVASSEUR, H. BROWMAN, 1998. An experimental tool for the study of the effects of ultraviolet radiation on planktonic communities : a mesocosm approach.. Environ. Technol., 19: 667-682 .

PEREZ, C., S. ROY, M. LEVASSEUR, D.M. ANDERSON, 1998. Control of germination of Alexandrium tamarense cysts from the Lower St. Lawrence Estuary (Canada). J. Phycol., 34: 242-249 .

GOSSELIN, M., M. LEVASSEUR, P.A. WHEELER, R. HORNER, B.C. BOOTH, 1998. New measurements of phytoplankton and ice algal production in the Arctic Ocean. Deep-Sea Res., Part II, Top. Stud. Oceanogr., 44(8): 1623-1644 .

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 .

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 .

FUENTES-YACO, C., A.F. VÉZINA, P. LAROUCHE, C. VIGNEAU, M. GOSSELIN, M. LEVASSEUR, 1997. Phytoplankton pigment in the Gulf of St. Lawrence, Canada, as determined by the Coastal Zone Color Scanner - Part I : Spatio-temporal variability. Cont. Shelf Res., 17(12): 1421-1439 .

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 .

SIME-NGANDO, T., M. GOSSELIN, S.K. JUNIPER, M. LEVASSEUR, 1997. Changes in sea-ice phagotrophic microprotists (20-200 µm) during the spring algal bloom, Canadian. J. Mar. Syst., 11: 163-172 .

DAUCHEZ, S., L. LEGENDRE, L. FORTIER, M. LEVASSEUR, 1996. Nitrate uptake by size-fractionated phytoplankton on the Scotian Shelf (Northwest Atlantic): spatial and temporal variability. J. Plankton Res., 18(4): 577-595 .

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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A mortality of Atlantic mackerel reported in Cape Breton in May 1993 prompted us to determine if paralytic shellfish poisoning (PSP) toxins could be identified as a potential cause of the kill. Live and dead mackerel collected in nearby traps had similar levels of PSP toxins in their livers. Additional mackerel were sampled from the commercial fishery in the southern and northern Gulf of St. Lawrence from June to October 1993. The total amount of PSP toxin per liver increased gradually with the age and the length of the fish, showing that mackerel bioaccumulate PSP toxins in their livers throughout their life. The quantity of PSP toxins per liver also increased during the summer, indicating that mackerel become comtaminated during their summer stay in the Gulf of St. Lawrence. By storing toxins in the liver, mackerel become potential lethal PSP vectors to their natural predators. However, eating mackerel poses no risk for humans as long as viscera are not consumed.

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) .

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 .

BLASCO, D., L. BÉRARD-THERRIAULT, M. LEVASSEUR, E. G. VRIELING, 1996. Temporal and spatial distribution of the ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt in the St. Lawrence, Canada. J. Plankton Res., 18: 1917-1930 .

DAUCHEZ, S., L. LEGENDRE, L. FORTIER, M. LEVASSEUR, 1996. New production and production of large phytoplankton (<5 µm) on the Scotian Shelf (Northeast Atlantic). Mar. Ecol. Prog. Ser., 135: 215-222 .

MICHEL, C., L. LEGENDRE, R.G. INGRAM, M. GOSSELIN, M. LEVASSEUR, 1996. Carbon budget of sea-ice algae in spring : evidence of a signifiant transfer to zooplankton grazers (Resolute Passage, Canadian Arctic).. J. Geophys. Res. (C Oceans), 101(C8): 18345-18360 .

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 .

GOSSELIN, S., M. LEVASSEUR, D. GAUTHIER, 1995. Transport and deballasting of toxic dinoflagellates via ships in the Grande Entree Lagoon of the Iles-de-la-Madeleine (Gulf of Saint-Lawrence, Canada). Pages 591-596 in 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.D. KELLER, E. BONNEAU, D. D'AMOURS, W.K. BELLOWS, 1994. Oceanographic basis of a DMS-related Atlantic cod (Gadus morhua) fishery problem : blackberry feed. Can. J. Fish. Aquat. Sci., 51: 881-889 .

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

LEVASSEUR, M., P.A. THOMPSON, P.J. HARRISON, 1993. Physiological acclimation of marine phytoplankton to different nitrogen sources. J. Phycol., 29: 587-595 .

HUPPERTZ, B., M. LEVASSEUR, 1993. Monitorage du phytoplancton dans l'estuaire et le golfe du Saint-Laurent en 1990. Rapp. tech. can. sci. halieut. aquat., 1922, 51 p .

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Since 1989, about ten stations located in the Estuary and the northern Gulf of St. Lawrence are monitored between June and November to determine the presence of the toxic algae Alexandrium spp., Dinophysis spp. and Nitzschia pungens forma multiseries. In 1990, blooms of Alexandrium spp., occurred at the end of June at relatively low concentration. As observed in 1989, the distribution of Alexandrium spp. was restricted to the plumes of the Manicouagen and Aux-Outardes Rivers and to the Gaspe Current. Very low concentrations of Alexandrium spp. were recorded along the Quebec's Lower North Shore and at the Magdalen Islands. Dinophysis spp. was observed all over the territory at very low concentrations. Nitzschia pungens forma multiseries was not found in the area of study.

BUGDEN, G., R. FORBES, D.C. GORDON, B. HUPPERTZ, P.D. KEIZER, M. LEVASSEUR, J.L. MARTIN, R. PENNEY, J.C. SMITH, D.V.S. RAO, D.J. WILDISH, P. YEATS, 1992. Overview of canadian phytoplankton monitoring programs. Pages 105-118 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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CEMBELLA, A.D., E. BERDALET, M.W. GILGAN, J.S.S. LAKSHMINARAYANA, C. LÉGER, M. LEVASSEUR, A. ORR, R. SELVIN, K. SOHET, D.V.S. RAO, E. TODD, 1992. Diarrhetic shellfish poisoning in Canada. Pages 57-65 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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LEVASSEUR, M., L. FORTIER, J.-C. THERRIAULT, P.J. HARRISON, 1992. Phytoplankton dynamics in a coastal jet frontal region. Mar. Ecol. Prog. Ser., 86: 283-295 .

FORTIER, L., M.E. LEVASSEUR, R. DROLET, J.-C. THERRIAULT, 1992. Export production and the distribution of fish larvae and their prey in a coastal jet frontal region. Mar. Ecol. Prog. Ser., 85: 203-218 .

THERRIAULT, J.-C., M. LEVASSEUR (ed.), 1992. Proceedings of the Third Canadian Workshop on Harmful Marine Algae, Maurice Lamontagne Institute, Mont-Joli, Quebec, 12-14 May, 1992. Can. Tech. Rep. Fish. Aquat. Sci., 1893,154 p .

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The Third Canadian Workshop on Harmful Marine Algae was hosted by the Department of Fisheries and Oceans, Québec region, at the Maurice Lamontagne Institute, Mont-Joli, on 12-14 May 1992. The workshop was attended by over 80 canadian and foreign participants and was aimed at a more efficient exchange of information on the latest developments concerning the subject of marine harmful algae in canadian waters. The main focus of the Workshop was "Harmful Algal Products : Impacts on the Food Web, Fisheries and Aquaculture". The present proceedings contain : 1) the abstracts of the oral and poster presentation; 2) the six reports from the Working Groups that were set up for general discussion on the following subjects : Origin and Propagation of Harmful Algae, Transfer of Phycotoxins in the Food Web, Detection and Quantification of Toxic Algae and Toxins, and Monitoring and Prediction of Harmful Events; 3) a conclusion chapter summarizing and emphasizing the most important recommendations from the Working Groups; and finally, in annex 4) two reviews highlighting the monitoring and phycotoxin programs in each DFO region, accompanied by a listing of National Working Hypotheses. A list of participants and an index of authors complete the proceedings.

LEVASSEUR, M.E., J.-C. MORISSETTE, R. POPOVIC, P.J. HARRISON, 1990. Effects of long term exposure to low temperature on the photosynthetic apparatus of Dunaliella tertiolecta Clorophyceae. J. Phycol., 26: 479-484 .

LEVASSEUR, M.E., P.J. HARRISON, B.R. HEIMDAL, J.-C. THERRIAULT, 1990. Simultaneous nitrogen and silicate deficiency of a phytoplankton community in a coastal jet-front. Mar. Biol., 104: 329-338 .

THOMPSON, P.A., M.E. LEVASSEUR, P.J. HARRISON, 1989. Light-limited growth on ammonium vs nitrate : what is the advantage for marine phytoplankton?. Limnol. Oceanogr., 34: 1014-1024 .

LEVASSEUR, M.E., J.-C. THERRIAULT, 1987. Phytoplankton biomass and nutrient dynamics in a tidally induced upwelling : the role of the NO3> :  SiO4 ratio. Mar. Ecol. Prog. Ser., 39: 87-97 .

THERRIAULT, J.-C., M. LEVASSEUR, 1986. Freshwater runoff control of the spatio-temporal distribution of phytoplankton in the Lower St. Lawrence Estuary (Canada). Pages 251-260 in S. Skreslet (ed.). The role of freshwater ouflow in coastal marine ecosystems. Springer-Verlag, Berlin (NATO Advanced Study Institutes Series. Series G, Ecological Sciences, 7) .