Search

11 pages, 6 figures, 1 table, The effects of harmful algae on bivalve physiology are complex and involve both physiological and behavioural responses. Studying those responses is essential to better describe and predict their impact on shellfish aquaculture and health risk for humans. In this study we recorded for two months the physiological response of the blue mussel Mytilus edulis from Eastern Canada to a one-week exposure to a paralytic shellfish poisoning producing dinoflagellate strain of Alexandrium catenella, isolated from the St Lawrence estuary, Canada. Mussels in a ‘control’ treatment were fed continuously with a non-toxic diet, while mussels in a ‘starvation’ treatment were fed the same non-toxic diet the first week and subsequently starved for seven weeks. Mussels in a ‘toxic’ treatment received A. catenella for one week before being starved until the end of the experiment. Over a two-month experiment we monitored shell and tissue growth, filtration capacity, respiration rate, byssal attachment strength, valve opening behaviour, and toxin content in tissues. Mussels fed normally on the toxic dinoflagellate and accumulated an average of 51.6 µg STXeq 100 g–1 after one week of exposure. After seven weeks of depuration, about half of the specimen showed levels around 18 µg STXeq 100 g–1. The condition index of exposed mussels (‘toxic’ treatment) decreased rapidly from the start as compared to mussels that received a one-week non-toxic diet (‘starvation’ treatment). Oxygen consumption rates increased in the ‘toxic’ treatment before leveling out with that of mussels from the ‘starvation’ treatment. Valve opening amplitude was lower in the ‘toxic’ treatment during and following the exposure. Average valve closure duration was higher right after the exposure, during the peak of mussel tissue intoxication. No significant change in byssal thread strength was observed through time in each treatment but less force was required to detach mussels from the ‘toxic’ and ‘starvation’ treatments. The number of byssus threads produced by mussels exposed to the toxic dinoflagellate was also lower than in the control group. These results represent advancements in our understanding of the impacts of harmful algae on bivalves and contribute to the development of mitigation measures necessary to both the safety of consumers and the sustainability of aquaculture operations, This project was undertaken with the financial support of the Government of Canada, specifically by Environment and Climate Change Canada (FDE-CA-2017i002) and Fisheries and Oceans Canada

The objective of this study was to assess experimentally the potential impact of anthropogenic pH perturbation (ApHP) on concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP), as well as processes governing the microbial cycling of sulfur compounds. A summer planktonic community from surface waters of the Lower St. Lawrence Estuary was monitored in microcosms over 12 days under three pCO2 targets: 1 × pCO2 (775 µatm), 2 × pCO2 (1,850 µatm), and 3 × pCO2 (2,700 µatm). A mixed phytoplankton bloom comprised of diatoms and unidentified flagellates developed over the course of the experiment. The magnitude and timing of biomass buildup, measured by chlorophyll a concentration, changed in the 3 × pCO2 treatment, reaching about half the peak chlorophyll a concentration measured in the 1 × pCO2 treatment, with a 2-day lag. Doubling and tripling the pCO2 resulted in a 15% and 40% decline in average concentrations of DMS compared to the control. Results from 35S-DMSPd uptake assays indicated that neither concentrations nor microbial scavenging efficiency of dissolved DMSP was affected by increased pCO2. However, our results show a reduction of the mean microbial yield of DMS by 34% and 61% in the 2 × pCO2 and 3 × pCO2 treatments, respectively. DMS concentrations correlated positively with microbial yields of DMS (Spearman’s ρ = 0.65; P < 0.001), suggesting that the impact of ApHP on concentrations of DMS in diatom-dominated systems may be strongly linked with alterations of the microbial breakdown of dissolved DMSP. Findings from this study provide further empirical evidence of the sensitivity of the microbial DMSP switch under ApHP. Because even small modifications in microbial regulatory mechanisms of DMSP can elicit changes in atmospheric chemistry via dampened efflux of DMS, results from this study may contribute to a better comprehension of Earth’s future climate.

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900 μatm, at two temperatures (in situ and C5 °C; 10 and 15 °C) were monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, warming the water by 5 °C resulted in a significant increase in the average bacterial production (BP) in all 15 °C mesocosms as compared to 10 °C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt DparticulateCdissolved DMSP) concentrations tracked the development of the bloom, although the rise in DMSPt persisted for a few days after the peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low concentrations of DMS (< 1 nmol L-1) increased to reach peak values ranging from 30 to 130 nmol L-1 towards the end of the experiment. Increasing the pCO2 reduced the averaged DMS concentrations by 66%and 69%at 10 and 15 °C, respectively, over the duration of the experiment. On the other hand, a 5 °C warming increased DMS concentrations by an average of 240% as compared to in situ temperature, resulting in a positive offset of the adverse pCO2 impact. Significant positive correlations found between bacterial production and concentrations of DMS throughout our experiment point towards temperatureassociated enhancement of bacterial DMSP metabolism as a likely driver of the mitigating effect of warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean. Fil: Benard, Robin. Laval University; Canadá Fil: Ferreyra, Gustavo Adolfo. Laval University; Canadá Fil: Michael, Scarratt. Maurice Lamontagne Institute, Fisheries And Oceans; Canadá Fil: Sonia, Michaud. Maurice Lamontagne Institute, Fisheries And Oceans ; Canadá Fil: Michel, Starr. Maurice Lamontagne Institute, Fisheries And Oceans; Canadá Fil: Alfonso, Mucci. Université Mcgill; Canadá Fil: Ferreyra, Gustavo Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Gosselin, Michel. Institut Des Sciences de la Mer de Rimouski; Canadá Fil: Tremblay, Jean-Éric. Laval University; Canadá Fil: Lizotte, Martine. Laval University; Canadá Fil: Yang, Gui Peng. Ocean University; China

The ecological conditions and cellular mechanisms which affect the production of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in marine ecosystems are still enigmatic. This information is crucial for deriving accurate oceanic ecosystem models for the dynamics of these major players in the Earth’s sulfur cycle and climate. In the present study, we examined the effect of short-term increases in photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) on the production of DMSP and DMS and on DMSP lyase potential activity (DLPA) in an axenic culture of the coccolithophore Emiliania huxleyi (CCMP 1742). Algal cells were subjected to a rapid shift from a low intensity of PAR (50 μE m-2 s-1; low light, LL) to a high intensity of PAR (198 μE m-2 s-1) and elevated UVR conditions (high light, HL), simulating what may occur during upward mixing in the surface mixed layer or during changes in cloud cover. During the 4.5 h exposure to HL, the intracellular DMSP normalized to cell volume increased by ca. 30%, and dissolved DMSP doubled relative to control values. However, the DLPA per unit of cell volume decreased by ~45% compared to the control value. The up-regulation of cellular DMSP concentration is consistent with an antioxidant and/or energy dissipation role for DMSP. The decrease in DLPA may indicate that the DMSP lyase enzyme plays no role in antioxidant protection in this algal species, but rather serves some other cellular function, such as grazing protection.

Following heavy precipitation, we observed an intense algal bloom in the St. Lawrence Estuary (SLE) that coincided with an unusually high mortality of several species of marine fish, birds and mammals, including species designated at risk. The algal species was identified as Alexandrium tamarense and was determined to contain a potent mixture of paralytic shellfish toxins (PST). Significant levels of PST were found in the liver and/or gastrointestinal contents of several carcasses tested as well as in live planktivorous fish, molluscs and plankton samples collected during the bloom. This provided strong evidence for the trophic transfer of PST resulting in mortalities of multiple wildlife species. This conclusion was strengthened by the sequence of mortalities, which followed the drift of the bloom along the coast of the St. Lawrence Estuary. No other cause of mortality was identified in the majority of animals examined at necropsy. Reports of marine fauna presenting signs of neurological dysfunction were also supportive of exposure to these neurotoxins. The event reported here represents the first well-documented case of multispecies mass mortality of marine fish, birds and mammals linked to a PST-producing algal bloom.