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The Arctic Ocean is currently undergoing significant transformations due to climate change, leading to profound changes in its microbial planktonic communities. These communities consist of a wide range of organisms, including photoautotrophic prokaryotes and eukaryotes, as well as heterotrophic, phagotrophic, and mixotrophic protistan species. Here, for simplicity, we refer to these single-celled species as phytoplankton. Within this diversity, potentially toxic and/or harmful algal species (hereafter abbreviated as "HA") are of particular concern. These organisms have the potential to spread into Arctic waters, posing threats to both human and ecosystem health. Despite their importance, the spatial and temporal distribution of phytoplankton communities, including HA species, in the North American Arctic, remains poorly understood. To address this gap, we compiled and synthesized the largest possible body of data from different databases, individual published and unpublished datasets, and partitioned it into nine regions based on the Large Marine Ecosystem classification. Our dataset contains 385 800 individual georeferenced data points and 18 268 unique sampling events, revealing greater diversity than previously thought, with 1445 unique taxa. Heterokontophyta (which notably included diatoms) and Dinoflagellata were the most dominant phyla. Our results indicate distinct spatial patterns of diversity, with the highest diversity observed in Atlantic-influenced regions of the North American Arctic. For most of the HA species recorded in our database, no evidence was found for an increase in the northernmost latitude where HA species are observed over the years, meaning that there is no substantial spread of HA species into the North American part of the Arctic. Our study challenges the traditional view of the Arctic as being unsuitable for toxin-producing and harmful algae and highlights the importance of extensive and long-term sampling efforts to understand the region's biodiversity. Overall, our findings provide new insights into the spatial patterns and biodiversity of phytoplankton and other protists in the North American Arctic and have implications for understanding the ecological functioning and response of this region to ongoing climate change. [ABSTRACT FROM AUTHOR]

In August 2019, visual inspection of intertidal zones of the Gulf of Maine (ME, USA) revealed young and adult wild blue mussels, Mytilus spp., in Alley Bay (Jonesport area) with the distinctive L‐shaped shell deformity (LSSD) and green spots (GS) in the mantle and adductor muscle. LSSD is a characteristic sign of current or previous mussel infection by photosynthetic unicellular alga from the group Coccomyxa, while GS are algal colonies. Based on these findings, this study represents the first report of infection signs by pathogenic Coccomyxa‐like algae in mussels from the coastal waters of the Northeastern United States, providing a base for future large scale monitoring of the alga in the region. [ABSTRACT FROM AUTHOR]

The rapid physical changes affecting the Arctic Ocean alter the growth conditions of primary producers. In this context, a crucial question is whether these changes will affect the composition of phytoplankton communities, augment their productivity, and eventually enhance food webs. We combined satellite and model products with in situ datasets collected during fall and provide new insights into the response of phytoplankton biomass and production in the Canadian Arctic by comparing an interior shelf (Beaufort Sea) and an outflow shelf (Baffin Bay). Correlation analysis was used to distinguish between seasonal and interannual variability and revealed that most biological variables are responding to the interannual pressures of climate change. In southeast Beaufort Sea, a change in phytoplankton community composition occurred, with a significant increase in diatoms from 2% (2002) to 37% (2010-2011) of the total protist abundance. In 2011, photosynthetic picoeukaryotes were twice as abundant as in 2002. For these two phytoplankton groups, abundance was correlated with the duration of the open-water period, which also increased and affected vertical stratification and sea-surface temperature. In contrast, there was a sharp decline in centric diatom abundance as well as in phytoplankton biomass and production in northern Baffin Bay over the years considered. These decreases were linked to changes in seasonal progression and sea-ice dynamics through their impacts on vertical stratification and freshwater input. Overall, our results highlight the importance of stratification and the duration of the open-water period in shaping phytoplankton regimes-either oligotrophic or eutrophic-in marine waters of the Canadian Arctic. [ABSTRACT FROM AUTHOR]

Presents a letter to the editor about bleeding perianal varices.

A letter to the editor is presented in response to an article by Andrew Harrop on the gender of the Poecile and the scientific name of the willow tit which appeared in a previous issue.

The distribution of dissolved organic carbon (DOC) in Hudson Bay (HB), Foxe Basin (FB), and Hudson Strait (HS) was examined during 01-14 August 2003. The HB system displayed relatively high DOC concentrations with medians of 109, 90, and 100 mmol L-1 for measurements made in HB, FB, and HS, respectively. Waters were significantly modified as they circulated through the HB system. An influence of marine-derived DOC was inferred for waters entering the system from northern HS and FB. The presence of a cold-water layer and elevated DOC concentrations observed in HB along the western coast and at depth was explained through either brine rejection and export of surface DOC to depth during sea ice formation or the decomposition of a settling algal bloom. As waters circulated in HB, an input of terrigenous DOC was the dominant modifying factor. In particular, DOC-laden rivers in southern HB increased the DOC concentration and then displayed a conservative behavior as water exited the bay along the southern coast of HS. Additionally, the late stages of ice melt observed during this study showed a significant dilution effect on surface DOC concentrations within eastern HB. Input and export of riverine DOC in the HB system was estimated at ∼5.5 Tg C yr-1, which is approximately 23% of the annual DOC input from rivers draining directly into the central Arctic Ocean and therefore represents an important contribution of terrigenous carbon to northern seas. [ABSTRACT FROM AUTHOR]

We measured the isotopic composition and accumulation of particulate organic matter (POM) and the uptake of carbon (C) and nitrogen (N) in an early bloom of the most productive recurring polynya of the Arctic Ocean. The estimated compensation irradiance at the onset of the bloom was similar to the average for the North Atlantic Ocean, implying that shallow mixing was of critical importance for the bloom's early initiation. Planktonic POM had a much lower σ13C than ice POM, suggesting that ice-algae contributed little to the pelagic biomass. The overall isotopic fractionation of pelagic N during bloom development was consistent with in situ diatom growth under saturating irradiance and limiting NO3-. Soon after the ice cleared, rapid physiological changes induced an order of magnitude increase in the C and NO3- uptake capacity of diatoms, leading to very high ƒ ratios (NO3- uptake : total N uptake). Most of the NO3- taken up appeared in the POM, so that little net release of reduced N occurred during the period of active growth. Given the tight coupling between photosynthesis and NO3- uptake under N limitation, the magnitude of primary production in the Arctic Ocean is expected to respond to changes in N supply. [ABSTRACT FROM AUTHOR]

Climate changes in the Arctic are expected to decrease the currently tight pelagic–benthic coupling, yet large-scale, regional understanding of the origin of food for benthic organisms across both biological productivity and depth gradients is still missing. The organic matter assimilation pathways of benthic organisms, along with food-web structure, were investigated at shelf and slope locations spanning 2000 km across the Canadian Arctic using stable carbon and nitrogen isotope analysis. Three potential food sources and over 75 benthic taxa belonging to four feeding guilds were analyzed, but the δ 13 C end-members for the benthic food-webs could not be clearly discerned. While spatial patterns of δ 13 C for pelagic particulate organic matter were linked to phytoplankton biomass at the time of sampling, sediment δ 13 C values reflected the relative composition of terrestrial and marine organic matter. On average, benthic primary consumers were enriched in 13 C by 5 and 7‰ compared to the potential organic matter sources sampled in sediment and the water column, respectively. The δ 13 C discrepancy between identified sources of organic matter and benthic organisms suggests that an uncharacterized food source provided a significant carbon source to these animals. We propose that the 13 C enrichment of benthic organisms may be largely caused by the assimilation of ice algae (which were not sampled in this study), particularly in regions of known high ice-algal standing stock such as Barrow Strait and Eclipse Sound. The δ 15 N values of bottom-water particulate organic matter and of benthic primary consumers increased with depth due to greater degradation of the settling organic material. The δ 15 N values of secondary consumers did not increase with depth, leading to a decrease of their trophic position compared with shallower regions and likely reflecting an increase in omnivory due to scarcity of prey at depth. This study emphasizes the potential importance of sea-ice algae as a carbon source for benthic communities in the Canadian Arctic and suggests that distinct food-web structures prevail over the shelf and slope. [ABSTRACT FROM AUTHOR]

Abstract: Zooplankton communities were examined for the first time in three different hydrographic regions of the Hudson Bay system (HBS) in early August to early September from 2003 to 2006. Sampling was conducted at 50 stations distributed along different transects located in Hudson Bay (HB), Hudson Strait (HS), and Foxe Basin (FB). Variations in zooplankton biomass, abundance, taxonomic composition, and diversity in relation to environmental variables were studied using multivariate techniques. During all sampling years, the total zooplankton biomass was on average four times lower in HB than in HS and FB. Clustering samples by their relative species compositions revealed no interannual variation in zooplankton community but showed a marked interregional variability between the three regions. Water column stratification explained the greatest proportion (25%) of this spatial variability. According to redundancy analysis (RDA), the zooplankton taxa that contribute most to the separation of the three regions are Microcalanus spp., Oithona similis, Oncaea borealis, Aeginopsis laurentii, Sagitta elegans, Fritillaria sp., and larvae of cnidaria, chaetognatha, and pteropoda in HB; hyperiid amphipods in FB; and Pseudocalanus spp. CI–CV, Calanus glacialis CI–CVI, Calanus finmarchicus CI–CVI, Calanus hyperboreus CV–CVI, Acartia longiremis CI–CV, Metridia longa N3-N6 CI-CIII CVIf, Eukrohnia hamata, larvae of echinodermata, mollusca, cirripedia, appendicularia, and polychaeta in the northwestern and southeastern HS transects. For the HB transect, the RDA analyzed allowed us to distinguish three regions (HB west, central, and east) with different environmental gradients and zooplankton assemblages, in particular higher concentration of Pseudocalanus spp. nauplii and CI–CVI, as well as benthic macrozooplankton and meroplankton larvae in western HB. In HS, Calanoid species (mainly C. finmarchicus and C. glacialis) were mostly observed at the north shore stations associated with the weakly stratified Arctic–North Atlantic waters coming from southwestern Davis Strait (inflow). In general, the RDA models tested among the HBS regions were very consistent with its general surface circulation pattern for summer conditions in terms of environmental variables and distinct zooplankton assemblages. Overall, zooplankton biomass and diversity indices (H′, J′, and S) were lower in the most stratified environment (i.e., HB) than in the deeper (FB) and more dynamic (HS) regions. The results of this work clearly show that the spatial differentiation and structure of the zooplankton communities are strongly influenced by the hydrodynamic conditions in the HBS that, trough their actions on temperature, salinity, stratification, mixing conditions and depth strata, lead to the spatial differentiation of these communities. [Copyright &y& Elsevier]

Abstract: We present a first attempt of simulating the sympagic and planktonic production cycles in the Hudson Bay marine system (HBS) driven by ice cover duration and local hydrodynamics with the help of a 3D coupled biological–physical model. The simulation shows a marked spatial variability of ice and planktonic production and associated carbon fluxes, suggesting the co-existence of several sub-systems in the HBS. Among these, the “low ice–high mixing” Hudson Strait sub-system is characterized by high (low) planktonic (ice algae) production, with annual primary production reaching up to 150g Cm−2 y−1. In contrast, the “high ice–low mixing” conditions over Hudson Bay induce an annual primary production of ca. 10–40g Cm−2 y−1 with a strong and early ice algal bloom. New production generally prevails over the simulated system except along the coastal freshwater-influenced southeastern Hudson Bay and shallow Foxe Basin. In most of the HBS, summer conditions are characterized by the prominence of deep chlorophyll and biomass maxima (down to 60m depth in the Hudson Bay) located near the nutricline. Finally, the residence time of the particulate organic matter and further export to the benthos appear driven by coupled advective and bathymetric effects. [Copyright &y& Elsevier]

Abstract: An understanding of microbial interactions in first-year sea ice on Arctic shelves is essential for identifying potential responses of the Arctic Ocean carbon cycle to changing sea-ice conditions. This study assessed dissolved and particulate organic carbon (DOC, POC), exopolymeric substances (EPS), chlorophyll a, bacteria and protists, in a seasonal (24 February to 20 June 2004) investigation of first-year sea ice and associated surface waters on the Mackenzie Shelf. The dynamics of and relationships between different sea-ice carbon pools were investigated for the periods prior to, during and following the sea-ice-algal bloom, under high and low snow cover. A predominantly heterotrophic sea-ice community was observed prior to the ice-algal bloom under high snow cover only. However, the heterotrophic community persisted throughout the study with bacteria accounting for, on average, 44% of the non-diatom particulate carbon biomass overall the study period. There was an extensive accumulation of sea-ice organic carbon following the onset of the ice-algal bloom, with diatoms driving seasonal and spatial trends in particulate sea-ice biomass. DOC and EPS were also significant sea-ice carbon contributors such that sea-ice DOC concentrations were higher than, or equivalent to, sea-ice-algal carbon concentrations prior to and following the algal bloom, respectively. Sea-ice-algal carbon, DOC and EPS-carbon concentrations were significantly interrelated under high and low snow cover during the algal bloom (r values≥0.74, p <0.01). These relationships suggest that algae are primarily responsible for the large pools of DOC and EPS-carbon and that similar stressors and/or processes could be involved in regulating their release. This study demonstrates that DOC can play a major role in organic carbon cycling on Arctic shelves. [Copyright &y& Elsevier]

Abstract: We examined the influence of the Mackenzie River plume on sinking fluxes of particulate organic and inorganic material on the Mackenzie Shelf, Canadian Arctic. Short-term particle interceptor traps were deployed under the halocline at 3 stations across the shelf during fall 2002 and at 3 stations along the shelf edge during summer 2004. During the two sampling periods, the horizontal patterns in sinking fluxes of particulate organic carbon (POC) and chlorophyll a (chl a) paralleled those in chl a biomass within the plume. Highest sinking fluxes of particulate organic material occurred at stations strongly influenced by the river plume (maximum POC sinking fluxes at 25 m of 98 mg C m−2 d−1 and 197 mg C m−2 d−1 in 2002 and 2004, respectively). The biogeochemical composition of the sinking material varied seasonally with phytoplankton and fecal pellets contributing considerably to the sinking flux in summer, while amorphous detritus dominated in the fall. Also, the sinking phytoplankton assemblage showed a seasonal succession from a dominance of diatoms in summer to flagellates and dinoflagellates in the fall. The presence of the freshwater diatom Eunotia sp. in the sinking assemblage directly underneath the river plume indicates the contribution of a phytoplankton community carried by the plume to the sinking export of organic material. Yet, increasing chl a and BioSi sinking fluxes with depth indicated an export of phytoplankton from the water column below the river plume during summer and fall. Grazing activity, mostly by copepods, and to a lesser extent by appendicularians, appeared to occur in a well-defined stratum underneath the river plume, particularly during summer. These results show that the Mackenzie River influences the magnitude and composition of the sinking material on the shelf in summer and fall, but does not constitute the only source of material sinking to depth at stations influenced by the river plume. [Copyright &y& Elsevier]

Abstract: Protist abundance and taxonomic composition were determined in four development stages of newly formed sea ice (new ice, nilas, young ice and thin first-year ice) and in the underlying surface waters of the Canadian Beaufort Sea from 30 September to 19 November 2003. Pico- and nanoalgae were counted by flow cytometry whereas photosynthetic and heterotrophic protists ≥4 µm were identified and counted by inverted microscopy. Protists were always present in sea ice and surface water samples throughout the study period. The most abundant protists in sea ice and surface waters were cells <4 µm. They were less abundant in sea ice (418–3051×103 cells L−1) than in surface waters (1393–5373×103 cells L−1). In contrast, larger protists (≥4 µm) were more abundant in sea ice (59–821×103 cells L−1) than in surface waters (22–256×103 cells L−1). These results suggest a selective incorporation of larger cells into sea ice. The ≥4 µm protist assemblage was composed of a total number of 73 taxa, including 12 centric diatom species, 7 pennate diatoms, 11 dinoflagellates and 16 flagellates. The taxonomic composition in the early stage of ice formation (i.e., new ice) was very similar to that observed in surface waters and was composed of a mixed population of nanoflagellates (Prasinophyceae and Prymnesiophyceae), diatoms (mainly Chaetoceros species) and dinoflagellates. In older stages of sea ice (i.e., young ice and thin first-year ice), the taxonomic composition became markedly different from that of the surface waters. These older ice samples contained relatively fewer Prasinophyceae and more unidentified nanoflagellates than the younger ice. Diatom resting spores and dinoflagellate cysts were generally more abundant in sea ice than in surface waters. However, further studies are needed to determine the importance of this winter survival strategy in Arctic sea ice. This study clearly shows the selective incorporation of large cells (≥4 µm) in newly formed sea ice and the change in the taxonomic composition of protists between sea ice and surface waters as the fall season progresses. [Copyright &y& Elsevier]

Climate changes in the Arctic may weaken the currently tight pelagic-benthic coupling. In response to decreasing sea ice cover, arctic marine systems are expected to shift from a 'sea-ice algae–benthos' to a 'phytoplankton-zooplankton' dominance. We used mollusc shells as bioarchives and fatty acid trophic markers to estimate the effects of the reduction of sea ice cover on the food exported to the seafloor. Bathyal bivalve Astarte moerchi living at 600 m depth in northern Baffin Bay reveals a clear shift in growth variations and Ba/Ca ratios since the late 1970s, which we relate to a change in food availability. Tissue fatty acid compositions show that this species feeds mainly on microalgae exported from the euphotic zone to the seabed. We, therefore, suggest that changes in pelagic-benthic coupling are likely due either to local changes in sea ice dynamics, mediated through bottom-up regulation exerted by sea ice on phytoplankton production, or to a mismatch between phytoplankton bloom and zooplankton grazing due to phenological change. Both possibilities allow a more regular and increased transfer of food to the seabed. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'. [ABSTRACT FROM AUTHOR]

The eastern James Bay (EJB) coast harbors numerous rivers, but there is a dearth of knowledge concerning dissolved organic matter (DOM) in the downstream coastal water. Here we report a four-year (2018–2021) and multi-seasons field study on the mixing behavior and characteristics of the chromophoric DOM (CDOM) in the nearshore EJB. Freshwater discharged from the extensively regulated La Grande River (LGR) was constantly depleted in DOM compared with the unregulated rivers (URRs), being on average 3.35 times lower in CDOM absorption coefficient at 440 nm (a CDOM (440)) and 2.50 times lower in dissolved organic carbon (DOC). In contrast, the absorption spectral slope between 275 and 295 nm (S 275–295 , a proxy of molecular weight) and the specific absorption coefficient at 254 nm (a * CDOM (254), an indicator of aromaticity) of the LGR CDOM were only 10.6% lower and 11.7% higher than those of the URRs CDOM, respectively. Riverine input was found to be the dominant source of CDOM in the study area, with little influence from sea ice formation or melting. CDOM distribution fell into two distinct regimes: the LGR-influenced low-CDOM area in the north and the URRs-influenced high-CDOM area in the south. The two areas showed strong conservative but separate a CDOM (440)–salinity relationships converging at a common marine endmember (salinity ∼25) with little seasonality. The composite data combing both areas and all seasons and years exhibited non-linear relationships between S 275–295 , a * CDOM (254) and a CDOM (440) and a robust simple linear correlation of DOC to a CDOM (440). This study suggests a strong impact of river regulation on CDOM input into the EJB, reveals low seasonal variability of CDOM mixing dynamics and characteristics, and demonstrates the feasibility of using remote sensing from space for real-time and synoptical assessment of DOM dynamics and the associated biogeochemical cycles in the EJB. • Strong depletion of CDOM in the regulated La Grande River vs. unregulated rivers • River regulation leads to distinct CDOM distribution and mixing patterns • Strong conservative CDOM mixing behavior with little seasonal variations • Robust linear correlation between DOC and CDOM free of seasonality • High potential for remote-sensing retrieval of DOC and CDOM characteristics [ABSTRACT FROM AUTHOR]

Sea ice is one of the most critical environmental drivers shaping primary production and fluxes of organic inputs to benthic communities in the Arctic Ocean. Fluctuations in organic inputs influence ecological relationships, trophic cascades, and energy fluxes. However, changes in sea-ice concentration (SIC) induced by global warming could lead to significant shifts in trophic interactions, ultimately affecting the functioning of Arctic food webs. Despite the increasing concern over the need to understand benthic species and food web responses to rapid sea-ice loss, few studies have addressed this topic so far. Using multiple niche metrics based on stable isotopes, this research examined the trophic ecology of epibenthic communities in areas with different SIC across the Canadian Arctic Ocean. We found that trophic niches varied according to complex interactions between environmental conditions, resource supply, and biotic pressures such as predation and competition. Our results highlighted a lower isotopic richness (i.e., shorter food chain length and niche width) in low and high SIC areas, suggesting homogeneity of resources and a low diversity of food items ingested by individuals. In contrast, a higher isotopic richness (i.e., broad niche) was observed in the moderate SIC area, implying higher heterogeneity in basal food sources and consumers using individual trophic niches. Finally, our findings suggested a lower isotopic redundancy in areas with high SIC compared to low and moderate SIC. Overall, our results support the idea that sea ice is an important driver of benthic food web dynamics and reinforce the urgent need for further investigations of declining sea ice cover impacts on Arctic food web functioning. [ABSTRACT FROM AUTHOR]

We determined, and compared, the abiotic stress state of algae and their attached bacterial communities following their release into the water column during the Arctic sea ice melt season using specific lipid markers that are characteristic of type II photo-oxidation processes, together with those associated with cis-trans isomerase and 10 S -DOX-like lipoxygenase activity, which are indicative of salinity stress. More specifically, parent lipids and some of their oxidation products were quantified in sinking particles (from sediment traps) collected from the Beaufort Sea, Resolute Passage and the Davis Strait (Canadian Arctic) in 2009, 2012 and 2015, respectively. Our data show that salinity- and light-induced bacterial stress processes are temporally decoupled, with the former occurring at the beginning of ice melting and the latter observed during the final stages of ice melt and in subsequent open waters. The salinity-induced bacterial stress seen during the early stages of ice melting contrasts the healthy state of sea ice algae under the same hypersaline conditions. As sea ice melt progresses, brine channels become hyposaline, thus reducing the bacterial salinity stress, while ice algae become susceptible to photodegradation by singlet oxygen ( 1 O 2 ), despite relatively low temperatures and irradiance. However, the presence of high amounts of extracellular polymeric substances (EPS) encapsulating the algae likely prevents the diffusion of 1 O 2 to the attached bacteria. Photo-oxidative stress is enhanced further in open waters due to the low amounts of EPS. The lower amounts of active bacteria in the Arctic compared to temperate or tropical regions is thus attributed to the combined action of efficient salinity stress in spring and photo-oxidative stress in summer. Outcomes from this study also imply that surface sediments from the Canadian Arctic contain relatively high quantities of sea ice-derived organic matter that has undergone a strong degree of salinity-induced stress. [ABSTRACT FROM AUTHOR]

Summertime Arctic shipboard observations of oxygenated volatile organic compounds (OVOCs) such as organic acids, key precursors of climatically active secondary organic aerosol (SOA), are consistent with a novel source of OVOCs to the marine boundary layer via chemistry at the sea surface microlayer. Although this source has been studied in a laboratory setting, organic acid emissions from the sea surface microlayer have not previously been observed in ambient marine environments. Correlations between measurements of OVOCs, including high levels of formic acid, in the atmosphere (measured by an online highresolution time-of-flight mass spectrometer) and dissolved organic matter in the ocean point to a marine source for the measured OVOCs. That this source is photomediated is indicated by correlations between the diurnal cycles of the OVOC measurements and solar radiation. In contrast, the OVOCs do not correlate with levels of isoprene, monoterpenes, or dimethyl sulfide. Results from box model calculations are consistent with heterogeneous chemistry as the source of the measured OVOCs. As sea ice retreats and dissolved organic carbon inputs to the Arctic increase, the impact of this source on the summer Arctic atmosphere is likely to increase. Globally, this source should be assessed in other marine environments to quantify its impact on OVOC and SOA burdens in the atmosphere, and ultimately on climate. [ABSTRACT FROM AUTHOR]

Highlights: [•] The biomarker IP25 identified in Arctic sea ice from different regions. [•] IP25-producing Arctic sea ice diatoms estimated to be 1–5%. [•] Sterols in Arctic sea ice identified and quantified. [•] Sea ice derived sterols likely to be significant in sediment budgets. [Copyright &y& Elsevier]

The influence of the seasonal development of microplankton communities on the cycling of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) was investigated along a South-North gradient (36-59N) in the Northwest (NW) Atlantic Ocean. Three surveys allowed the sampling of surface mixed layer (SML) waters at stations extending from the subtropical gyre to the Greenland Current during May, July and October 2003. Pools and transformation rates of DMSP and DMS were quantified and related to prevailing physical and biochemical conditions, phytoplankton abundance and taxonomic composition, as well as bacterioplankton abundance and leucine uptake. The South-North progression of the diatom bloom, a prominent feature in the NW Atlantic, did not influence the production of DMS whereas conditions in the N Atlantic Drift lead to a persistent bloom of DMSP-rich flagellate-dominated phytoplankton community and high net DMS production rates. Macroscale patterns of the observed variables were further explored using principal component analysis (PCA). The first axis of the PCA showed a strong association between the spatio-temporal distribution of DMSP and the abundance of several phytoplankton groups including dinoflagellates and prymnesiophytes, as well as with microbial-mediated DMSP consumption and yields and rates of the conversion of DMSP into DMS. The second axis revealed a strong association between concentrations of DMS and SML depth and photosynthetically active radiation, a result supporting the prominent role of solar radiation as a driver of DMS dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5±12.5gCm−2 calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5μm, 67.6%) over small cells (<5μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2gCm−2, which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9gCm−2, a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395m) supplied 60% of the estimated benthic C demand (2.8gCm−2), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6gCm−2). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain. [Copyright &y& Elsevier]

Abstract: This study investigates, for the first time, the role of free-living and particle-attached bacteria in the sinking export and recycling of organic matter in the Hudson Bay system (i.e. Hudson Bay, Hudson Strait, and Foxe Basin), a large subarctic estuarine system. During the late summers of 2005 and 2006, the abundance, cell size, nucleic acid content, and sinking velocity of free-living and particle-attached bacteria were studied simultaneously, using a new approach that combines the settling column method with flow cytometry. Biomass, production, and respiration of both types of bacteria were estimated using published models. Our results showed that particle-attached bacteria were, on average, twice as large as and contained 1.3 times more nucleic acid than free-living bacteria. Particle-attached bacteria also sank faster than predicted by Stoke''s Law, with estimated sinking velocities comparable to those of chlorophyll a biomass and protist cells. Each individual cell of the particle-attached bacterial community had high carbon demand, but their low abundances (<3% of total bacterial numbers) resulted in low total carbon demand. Therefore, the main contributors to POC recycling were found to be free-living bacteria using the non-sinking dissolved organic material, which is released from particles due to the hydrolytic activity of particle-attached bacteria. [Copyright &y& Elsevier]

Abstract: A steady-state model of the planktonic food web of the Bizerte Lagoon (Tunisia, South-western Mediterranean) was developed to characterize its structure and functioning through four stations: MA under urban discharge, MB impacted by industrial input, MJ located at proximity of shellfish farming and R in the central area of the lagoon. Carbon stocks of eight chosen compartments were determined and flows were assigned for each one from field data. Missing flow values were calculated by inverse analysis for each station. Network analysis was applied to the resulting food web models to characterize their properties. These analyses mainly showed similarity among stations concerning (1) a high primary production of phytoplankton which was dominated by >10μm cells (i.e. diatoms); (2) important herbivory against detritivory in stations MA and MJ; (3) major role of detritivory in stations MB and R; (4) efficiency of microbial link in transferring carbon for higher trophic level; (5) efficiency of microzooplankton as a trophic link between detritus, dissolved organic carbon, autotrophs and mesozooplankton; (6) important recycling of carbon leading to conclude about an immature state of the ecosystem. Differences between the functioning of microbial food webs in the lagoon are mainly due to the location of stations. The proximity of station MB to inland and industrial discharges affected its productivity and made it the least productive station. Water circulation into the lagoon made pollutant concentrate into the south and the western sections which seemed to affect the planktonic food web, since the values of productivity reported for stations MB and R were lower than those calculated for the others stations. [Copyright &y& Elsevier]

Abstract: The structure and the trophic interactions of the planktonic food web were investigated during summer 2004 in a coastal lagoon of south-western Mediterranean Sea. Biomasses of planktonic components as well as bacterial and phytoplankton production and grazing by microzooplankton were quantified at four stations (MA, MB, MJ and R) inside the lagoon. Station MA was impacted by urban discharge, station MB was influenced by industrial activity, station MJ was located in a shellfish farming sector, while station R represented the lagoon central area. Biomasses and production rates of bacteria (7–33mgCm−3; 17.5–35mgCm−3 d−1) and phytoplankton (80–299mgCm−3; 34–210mgCm−3 d−1) showed high values at station MJ, where substantial concentrations of nutrients (NO3 − and Si(OH)4) were found. Microphytoplankton, which dominated the total algal biomass and production (>82%), were characterized by the proliferation of several chain-forming diatoms. Microzooplankton was mainly composed of dinoflagellates (Torodinium, Protoperidinium and Dinophysis) and aloricate (Lohmaniellea and Strombidium) and tintinnid (Tintinnopsis, Tintinnus, Favella and Eutintinnus) ciliates. Higher biomass of these protozoa (359mgCm−3) was observed at station MB, where large tintinnids were encountered. Mesozooplankton mainly represented by Calanoida (Acartia, Temora, Calanus, Eucalanus, Paracalanus and Centropages) and Cyclopoida (Oithona) copepods, exhibited higher and lower biomasses at stations MA/MJ and MB, respectively. Bacterivory represented only 35% of bacterial production at stations MB and R, but higher fractions (65–70%) were observed at stations MA and MJ. Small heterotrophic flagellates and aloricate ciliates seemed to be the main controllers of bacteria. Pico- and nanophytoplankton represented a significant alternative carbon pool for micrograzers, which grazing represented 67–90% of pico- and nano-algal production in all stations. Microzooplankton has, however, a relatively low impact on microphytoplankton, as ≤45% of microalgal production was consumed in all stations. This implies that an important fraction of diatom production would be channelled by herbivorous meso-grazers to higher consumers at stations MA and MJ where copepods were numerous. Most of the microalgal production would, however, sink particularly at station MB where copepods were scare. These different trophic interactions suggest different food web structures between stations. A multivorous food web seemed to prevail in stations MJ and MA, whereas microbial web was dominant in the other stations. [Copyright &y& Elsevier]

Abstract: Understanding pathways of carbon cycling on Arctic shelves is critical if we are to evaluate the potential effects of climate change on these systems. We investigated the relationship between ice algal standing stock and benthic respiration between January and July 2004 at a time series station in the southeastern Beaufort Sea. Both ice algal chlorophyll a and benthic sediment oxygen demand showed >10-fold increases from between March and April. While some of the increase in oxygen demand can be attributed to bacteria and meio-fauna, most was due to the activities of macroinfauna. We also observed a trend toward lower sediment pigment content during the pulse in benthic carbon remineralization. While chl a sedimentation also increased by a factor of 7 during this period, fluxes were not sufficient to provide for the increased carbon demand. We suggest that sedimenting ice algae provided a cue for increased benthic activity, and that direct consumption of ice algae and increased oxygen availability in the sediment due to bioturbation by epifaunal organisms led to the enhancement in respiration rates. Seasonal patterns in primary productivity and the activity of resident epifaunal and infaunal communities are, thus, important factors in determining carbon cycling patterns on Arctic shelves. [Copyright &y& Elsevier]

A multi-institutional initiative was created in a context of potential oil exploration at the Old Harry site to monitor the marine ecosystem and manage resources of the Gulf of St. Lawrence (GSL). As part of this initiative, two sediment traps were deployed at depths of 34 m and 100 m at a site northwest of Cabot Strait in the Laurentian Channel to measure downward carbon fluxes from October 2014 to October 2015. Fluxes of particulate organic carbon (POC), biogenic silica (BSi), chloropigments, protists and zooplankton fecal pellets were used to evaluate vertical and temporal changes in the magnitude and composition of biogenic carbon fluxes and to provide baseline information prior to any exploration activities in the region. Peaks in POC, BSi, chloropigment and diatom fluxes at both depths at the end of April 2015 indicated the rapid export of a locally-produced bloom mainly composed of pennate diatoms. A coincident peak in fecal pellet carbon fluxes at 100 m indicated a match between the spring ascent of copepods and the diatom bloom. The distinct composition of protist fluxes at 34 and 100 m following the formation of the winter mixed layer highlighted the influence of the pycnocline as a physical barrier for the export of particles in the region. Among identifiable components, dinoflagellates and fecal pellets, followed by diatoms and foraminifera, contributed most to the annual POC flux at 100 m, indicating a balance between lateral advection of slow-sinking protists and rapid export of fast-sinking diatoms and fecal pellets in the supply of POC toward the seafloor in the GSL. These measurements of biogenic carbon export provide insight into the fate of large and small particles in the Cabot Strait region to consider in the potential development of oil and gas activities. • Traps were deployed over an annual cycle near Old Harry in the Gulf of St. Lawrence. • Peak export fluxes were recorded at 34 m and 100 m at the end of April 2015. • Annual flux of particulate organic carbon reached 1.1 g C m−2 yr−1 at 100 m. • Dinoflagellates and fecal pellets contributed most to particulate carbon fluxes. [ABSTRACT FROM AUTHOR]

• Shell deformity indicates intense infection of mytilid mussels with Coccomyxa -like algae. • Presence of green spots in mussel soft tissues is symptomatic of infection. • Shell deformity is a stable through-time mineral marker of Coccomyxa infection. • Algal colonization of host organisms may be reduced or even stopped. An L-shaped shell deformity (LSSD) on the posterior shell edge is known exclusively in wild mytilid mussels infected with photosynthetic Coccomyxa -like algae. LSSD forms due to the appearance of extra shell material; it only occurs if the mussel is heavily infected with the alga. Traditionally, observation of high amount of the green spots (algal colonies) on a large area of host soft tissues (most of the mantle and in adductor muscle) has been used to indicate a high infection rate. We examined 300 Mytilus spp. (100 small, 20–30 mm; 200 large, 40–60 mm) with a high degree of LSSD (parameter "d" > 5 mm) from the Lower St. Lawrence Estuary (Québec, Canada). Green spots were absent in two large mussels, and were only present along the mantle posterior edge in 14 large mussels; other individuals had high infection levels. Our observations suggest that some individuals could be in a state of remission, or, even more optimistically - mussels may be able to resist the pathogen. LSSD is the stable through-time marker for detection of mytilid mussels that are or were infected with Coccomyxa algae, and, thus, may provide information for the study of mussel immunity and control of alga distribution/migration in coastal waters worldwide. [ABSTRACT FROM AUTHOR]

As evidenced from literature, exposure to non-lethal concentrations of dissolved copper (Cu 2+ ) and copper nanoparticles (CuO NPs) promotes blue mussels susceptibility to various bacterial infections. We study whether pre-exposure (3.5 h) with CuSO 4 (100 μg Cu L -1 ) and CuO NPs (1000 μg Cu L -1 ) will result in infection of M. edulis L. with pathogenic microalga Coccomyxa sp. under field conditions. In May - September 2019, cages were installed in the site Metis-sur-Mer, St. Lawrence Estuary (QC, Canada) where the native mussel population is known to be infected with the pathogen. Untreated and pre-exposed mussels were grown for up to 130 days. Only the mussels pre-exposed to copper were infected by Coccomyxa. This finding allows proposing that occurrences of Coccomyxa-infected mussels worldwide might have an association with water pollution with xenobiotics. Pre-exposure of caged mussels to copper, as a protocol monitoring for other infectious agents, can be recommended to test., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Oceanic gateways are sensitive to climate driven processes. By connecting oceans, they have a global influence on marine biological production and biogeochemical cycles. The furthest north of these gateways is Nares Strait at the top of the North Water between Greenland and Ellesmere Island (Canada). This gateway is globally beneficial, first by supporting high local mammal and bird populations and second with the outflow of phosphate-rich Arctic waters fueling the North Atlantic spring bloom. Both sides of the North Water are hydrologically distinct with counter currents that make this Arctic portal a Janus gateway, after Janus, the Roman god of duality. We examined oceanographic properties and differences in phytoplankton and other protist communities from the eastern and western sides of the North Water (latitude 76.5°N) and found that species differed markedly due to salinity stratification regimes and local hydrography. Typical Arctic communities were associated with south flowing currents along the Canadian side, while potentially noxious Pseudo-nitzschia spp. were dominant on the Greenland side and associated with greater surface freshening from ice melt. This susceptibility of the Greenland side to Pseudo-nitzschia spp. blooms suggest that monitoring species responses to climate mediated changes is needed.

Unlabelled: Accuracy of preoperative imaging methods for the diagnosis of intraductal papillary mucinous tumor of the pancreas (IPMT) is not well known., Aims: To compare diagnostic accuracy of various preoperative imaging methods with pathology data following surgical resection., Patients and Methods: Fourteen consecutive patients underwent pancreatic surgical resection for IPMT between January 1988 and May 2002. Imaging methods included endoscopic retrograde cholangiopancreatography and/or magnetic resonance cholangiopancreatography and/or endoscopic ultrasonography. Results of preoperative morphological examinations were compared with histopathological findings from surgical specimens., Results: IPMT was located to the pancreatic head or body in 72% of patients and involved the main pancreatic duct (MPD) in 79% of cases Carcinoma was diagnosed in 35% of the cases. Sensitivity of imaging methods varied from 64 to 80% to accurately locate the tumor and from 73 to 80% in distinguishing between types involving the MPD or the accessory ducts. Planned surgical resection based on preoperative imagery correlated with final surgery in 57% of the patients. Histological study of whole pancreas specimens revealed lesions in undilated ducts, and also dilated ducts without histological lesions., Conclusion: The sensitivity of preoperative imaging methods is moderate in defining intraductal extension of IPMT. Duct dilatation is not predictive of histological involvement by tumors and ducts may be pathological without dilatation.

Non-steroidal anti-inflammatory drugs (NSAIDs) reduce prostaglandin synthesis by inhibiting cyclo-oxygenase 1 (COX-1) and/or cyclo-oxygenase 2 (COX-2). Different groups of NSAIDs, defined by their action on either COX-1 or COX-2, have been developed. Whether intestinal toxicity of preferential or selective COX-2 inhibitors is reduced compared with that of standard NSAIDs is controversial. We report the cases of two patients with self-limited colitis induced by preferential COX-2. We discuss the mechanisms of intestinal toxic effects of COX-2 preferential inhibitors from endoscopic and histological features of colitis.

Paroxysmal nocturnal hemoglobinuria is rarely associated with intestinal complications. We report a case of paroxysmal nocturnal hemoglobinuria with small bowel ischemia leading to ileal perforation. In the literature, an ulcerative jejuno-ileitis has been reported in 6 cases of intestinal ischemia, due to thrombosis of mucosal small vessels. This disease is usually revealed by abdominal pain. Based on published cases and our observation of intestinal ischemia leading to small bowel perforation, surgery should be considered as the first-line treatment, especially when small bowel lesions are limited.

We describe a case of Whipple's disease confirmed by clinical, histological, bacteriological and molecular criteria. The duodenal involvement was associated with the presence of an endoscopic and histological enterocolitis. Final diagnosis of small bowel and colonic involvement by Whipple's disease was confirmed by histology and molecular biology. We review the literature on extra duodenal involvement. We underline the fact that enterocolitis in Whipple's disease is non-specific. We also discuss the other causes of intestinal mucosal infiltration by macrophages.