Michel Starr

Acidification of Lower St. Lawrence Estuary Bottom Waters

Accumulation of metabolic CO2 can acidify marine waters above and beyond the ongoing acidification of the ocean by anthropogenic CO2. The impact of respiration on carbonate chemistry and pH is most acute in hypoxic and anoxic basins, where metabolic CO2 accumulates to high concentrations. The bottom waters of the Lower St. Lawrence Estuary (LSLE), where persistently severe hypoxia has developed over the last 80 years, is one such case. We have reconstructed the evolution of pH in the bottom waters from historical and recent data, and from first principles relating the stoichiometry of CO2 produced to oxygen consumed during microbial degradation of organic matter. Based on the value of the atmospheric partial pressure of CO2 that best reproduces the preformed dissolved inorganic carbon concentration in the bottom waters, we estimate the average ventilation age of the bottom waters to be 16 ± 3 years. The pH of the bottom waters has decreased by 0.2 to 0.3 over the last 75 years, which is four to six times greater than can be attributed to the uptake of anthropogenic CO2. The pH decrease is accompanied by a decline in the saturation state with respect to both calcite and aragonite. As of 2007, bottom waters in the LSLE are slightly supersaturated with respect to calcite (Ωc ≈ 1.06 ± 0.04) but are strongly undersaturated with respect to aragonite (Ωa ≈ 0.67 ± 0.03).

Effects of diatom diets on the reproduction of the planktonic copepod Calanus finmarchicus

The potential for an adverse influence of diatom diets on the reproductive success of the planktonic copepod Calanus finmarchicus was investigated experimentally under laboratory conditions. A monospecific diet of the common diatom Thalassiosira nordenskioldii significantly reduced the viability of Calanus eggs, which either failed to hatch or hatched into deformed nauplii. The production of nonviable eggs increased with increasing Thalassiosira concentration and was proportional to the female ingestion rate. At a cell concentration of 104 ml−1 (typical bloom concentration in the St. Lawrence Estuary), the proportion of nonviable eggs was as high as 83% of the total daily production Nonviable egg production was also induced by a diatom of the genus Navicula, but not by two other diatoms, Skeletonema costatum and Chaetoceros debilis. Among non-diatom diets, maternal feeding on a dinoflagellate (Prorocentrum micans) and two flagellates (Isochrysis galbana, Pavlova lutheri) at food-saturated conditions resul...

Seasonal versus synoptic variability in planktonic production in a high‐latitude marginal sea: The Gulf of St. Lawrence (Canada)

The Gulf of St. Lawrence (Canada) is a subarctic marginal sea characterized by highly variable hydrodynamic conditions that generate a spatial heterogeneity in the marine production. A better understanding of physical-biological linkages is needed to improve our ability to evaluate the effects of climate variability and change on the gulfs planktonic production. We develop a three-dimensional (3-D) eddy permitting resolution physical-biological coupled model of plankton dynamics in the Gulf of St. Lawrence. The planktonic ecosystem model accounts for the competition between simplified herbivorous and microbial food webs that characterize bloom and post-bloom conditions, respectively, as generally observed in temperate and subarctic coastal waters. It is driven by a fully prognostic 3-D sea ice-ocean model with realistic tidal, atmospheric, and hydrological forcing. The simulation shows a consistent seasonal primary production cycle, and highlights the importance of local sea ice dynamics for the timing of the vernal bloom and the strong influence of the mesoscale circulation on planktonic production patterns at subregional scales.

Low calcium carbonate saturation state in an Arctic inland sea having large and varying fluvial inputs: The Hudson Bay system

The Hudson Bay system (HBS) is a shallow inland sea in the Arctic, composed of Hudson Strait, Foxe Basin/Channel, James Bay, and Hudson Bay. Dissolved inorganic carbon (DIC) and total alkalinity (TA) measurements were used to investigate the state of ocean acidification, specifically calcium carbonate saturation states (Ω) and pH. The freshwater sources were identified from the relationship between oxygen isotope composition (δ18O) and salinity to understand the role of freshwater in ocean acidification. The saturation state of seawater with respect to calcium carbonate (Ω) in surface water ( 10%). The watershed characteristics, however, influenced the alkalinity of river runoff in different parts of Hudson Bay, which contributed to Ω variation in the coastal region. In southwestern Hudson Bay where the watershed is dominated by limestone, Ω was higher compared to eastern Hudson Bay, where the watershed consists of an igneous rock formation. In deeper waters, low Ω is caused by remineralization of organic matter. The highest DIC concentrations (>2300 µmol/kg) were observed in the depths of central Hudson Bay with a pHtotal of 7.49 and Ωarg of 0.37. Over 67% and 22% of the bottom water of Hudson Bay was undersaturated with respect to aragonite and calcite respectively, despite Hudson Bay being very shallow (less than 250 m deep). The aragonite saturation horizon in the central Hudson Bay was around 50 m.

Marine Mammal Strandings and Environmental Changes: A 15-Year Study in the St. Lawrence Ecosystem

Understanding the effects of climatic variability on marine mammals is challenging due to the complexity of ecological interactions. We used general linear models to analyze a 15-year database documenting marine mammal strandings (1994–2008; n = 1,193) and nine environmental parameters known to affect marine mammal survival, from regional (sea ice) to continental scales (North Atlantic Oscillation, NAO). Stranding events were more frequent during summer and fall than other seasons, and have increased since 1994. Poor ice conditions observed during the same period may have affected marine mammals either directly, by modulating the availability of habitat for feeding and breeding activities, or indirectly, through changes in water conditions and marine productivity (krill abundance). For most species (75%, n = 6 species), a low volume of ice was correlated with increasing frequency of stranding events (e.g. R2 adj = 0.59, hooded seal, Cystophora cristata). This likely led to an increase in seal mortality during the breeding period, but also to increase habitat availability for seasonal migratory cetaceans using ice-free areas during winter. We also detected a high frequency of stranding events for mysticete species (minke whale, Balaenoptera acutorostrata) and resident species (beluga, Delphinapterus leucas), correlated with low krill abundance since 1994. Positive NAO indices were positively correlated with high frequencies of stranding events for resident and seasonal migratory cetaceans, as well as rare species (R2 adj = 0.53, 0.81 and 0.34, respectively). This contrasts with seal mass stranding numbers, which were negatively correlated with a positive NAO index. In addition, an unusual multiple species mortality event (n = 114, 62% of total annual mortality) in 2008 was caused by a harmful algal bloom. Our findings provide an empirical baseline in understanding marine mammal survival when faced with climatic variability. This is a promising step in integrating stranding records to monitor the consequences of environmental changes in marine ecosystems over long time scales.

Spatial and temporal variability of ice algal production in a 3D ice–ocean model of the Hudson Bay, Hudson Strait and Foxe Basin system

Primary production, the basic component of the food web and a sink for dissolved inorganic carbon, is a major unknown in Arctic seas, particularly ice algal production, for which detailed and comprehensive studies are often limited in space and time. We present here a simple ice alga model and its coupling with a regional 3D ice–ocean model of the Hudson Bay system (HBS), including Hudson Strait and Foxe Basin, as a first attempt to estimate ice algal production and its potential contribution to the pelagic ecosystem on a regional scale. The ice algal growth rate is forced by sub-ice light and nutrient availability, whereas grazing and ice melt control biomass loss from the underside of the ice. The simulation shows the primary role of sea-ice dynamics on the distribution and production of ice algae with a high spatio-temporal variability in response to the great variability of ice conditions in different parts of the HBS. In addition to favourable light and nutrient conditions, there must be a sufficient time lag between the onset of sufficient light and ice melt to ensure significant ice algal production. This suggests that, in the context of enhanced warming in Arctic and sub-Arctic regions, earlier melt could be more damaging for ice algal production than later freezing. The model also includes a particulate organic matter (POM) variable, fed by ice melting losses to the water column, and shows a large redistribution of the POM produced by the ice ecosystem on a regional scale.

Mating of Snow Crab Chionoecetes Opilio (Ο. Fabricius, 1788) (Decapoda, Majidae) in the Fjord of Bonne Bay, Newfoundland

Pairs of male and female snow crabs, Chionoecetes opilio, in mating courtship embrace were collected by SCUBA diving between 1984 and 1991, and with tangle nets between 1987 and 1993 in the Bonne Bay fjord, Newfoundland. A Nephrops trawl was also used to study the snow crab population size structure between 1988 and 1993. Males in mating courtship embrace were all identified as hard-shell morphometrically mature. Although large hard-shell juvenile males were present in the population, they did not participate in the reproduction. Comparison of the size structure of males in mating pairs and in the population also show that small mature male crabs can be excluded from mating by larger dominant mature males. The size structure between females in mating pairs and in the population was not significantly different. A depth segregation by size on the very steep slope of the fjord was observed for male snow crabs in mating pairs, as smaller males were found above 50 m. There was no correlation between male and female size in mating couples, but males were always larger than females. We conclude that there is a strong intra-specific competition between males during mating in nature.

Multispecies mass mortality of marine fauna linked to a toxic dinoflagellate bloom

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.

Morphological and phylogenetic comparisons of Neodenticula seminae (Bacillariophyta) populations between the subarctic Pacific and the Gulf of St. Lawrence

Neodenticula seminae is a very important member of modern diatom assemblages in the Bering Sea and at middle to high latitudes of the North Pacific. In the North Atlantic, this species was considered extinct until it was recorded in high abundance in the 2001 spring phytoplankton bloom of the Gulf of St. Lawrence, Eastern Canada. Here, we discuss some of the most distinctive features of its morphology, including variation in some characters between the subarctic Pacific and the Gulf of St. Lawrence specimens. Most importantly, we observed that the deck and basal ridges, and the solid-walled costae (formerly known as primary pseudosepta) characteristic of N. seminae were present in the subarctic Pacific material, but were absent or vestigial in the Gulf of St. Lawrence material and in cultures from both regions. This morphological variation was most likely due to differences in physico–chemical water properties between the subarctic Pacific and the Gulf of St. Lawrence. Phylogenetic analyses of the internal transcribed spacer regions of the nuclear ribosomal DNA showed that the strains of N. seminae collected in the Gulf of St. Lawrence and the subarctic Pacific clustered in two sister clades, but differed from each other only slightly more than the variation among the subarctic Pacific strains. These results confirmed the reappearance of N. seminae in the NW Atlantic after an absence of ∼0.8 Ma. In addition, the phylogenetic analyses based on the large subunit of the nuclear ribosomal DNA positioned N. seminae firmly within the Bacillariaceae (i.e. diatoms with a fibulate raphe system) and proved a close relationship to species of Fragilariopsis.

Contrasting effects of acidification and warming on dimethylsulfide concentrations during a temperate estuarine fall bloom mesocosm experiment

The effects of ocean acidification and warming on the concentrations of dimethylsulfoniopropionate (DMSP) and 15 dimethylsulfide (DMS) were investigated during a mesocosm experiment in the Lower St. Lawrence Estuary (LSLE) in the 16 fall of 2014. Twelve mesocosms covering a range of pHT (pH on the total hydrogen ion concentration scale) from 8.0 to 7.2, 17 corresponding to a range of CO2 partial pressures (pCO2) from 440 to 2900 μatm, at two temperatures (in situ and +5 °C; 10 °C 18 and 15 °C) was monitored during 13 days. All mesocosms were characterized by the rapid development of a diatom bloom 19 dominated by Skeletonema costatum, followed by its decline upon the exhaustion of nitrate and silicic acid. Neither the 20 acidification nor the warming resulted in a significant impact on the abundance of bacteria over the experiment. However, 21 warming the water by 5 °C resulted in a significant increase of the average bacterial production (BP) in all 15 °C mesocosms 22 as compared to 10 °C, with no detectable effect of pCO2 on BP. Variations in total DMSP (DMSPt = particulate + dissolved 23 DMSP) concentrations tracked the development of the bloom although the rise in DMSPt persisted for a few days after the 24 peaks in chlorophyll a. Average concentrations of DMSPt were not affected by acidification or warming. Initially low 25 concentrations of DMS (< 1 nmol L) increased to reach peak values ranging from 30 to 130 nmol L towards the end of the 26 experiment. Increasing the pCO2 reduced the averaged DMS concentrations by 66 % and 69 % at 10 °C and 15 °C, 27 respectively, over the duration of the experiment. On the other hand, a 5 °C warming increased DMS concentrations by an 28 average of 240 % as compared to in situ temperature, resulting in a positive offset of the adverse pCO2 impact. Significant 29 positive correlations found between bacterial production rates and concentrations of DMS throughout our experiment point 30 towards temperature-associated enhancement of bacterial DMSP metabolism as a likely driver for the mitigating effect of 31 warming on the negative impact of acidification on the net production of DMS in the LSLE and potentially the global ocean. 32 Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-338 Manuscript under review for journal Biogeosciences Discussion started: 22 August 2018 c