Claude Belzile

An Experimental Tool to Study the Effects of Ultraviolet Radiation on Planktonic Communities: A Mesocosm Approach

A mesocosm approach was adopted for the study of the impact of UV-B radiation on coastal planktonic communities. Experiments were conducted in eight land-based 1500 1 mesocosms. The 2.25 m deep mesocosms reproduced the whole euphotic zone and vertical mixing ensured a homogeneous water column. While maintaining all other physical characteristics the same, UV-B levels were manipulated in different mesocosms by either increasing UV-B with lamps or by eliminating it using Mylar® sheet as a filter. The resulting spectral irradiance regime produced in the mesocosms was characterised by the daily irradiance averaged over the water column. Incident irradiance was measured every 10 minutes using an International Light IL-1700 radiometer and a Biospherical PUV-511 radiometer. Underwater spectral irradiance for the different treatments was determined using a Biospherical PUV-500 profiling radiometer. One of the present challenges of UV-B research is the extrapolation of results from laboratory and short-term field ...

INFLUENCE OF UV-B RADIATION ON NITROGEN UTILIZATION BY A NATURAL ASSEMBLAGE OF PHYTOPLANKTON

A 7‐day mesocosm experiment was conducted in July 1996 to investigate the effects of ambient UV‐B radiation (UVBR) exclusion and two UVBR enhancements above ambient levels on NO3−, NH4+ and urea utilization in a natural plankton community (<240 μm) from the Lower St. Lawrence Estuary. The phytoplankton community was dominated by diatoms during the first 3 days and, afterward, by flagellates and dinoflagellates. The results of 4‐h incubations just below the water surface show that, compared with ambient UVBR conditions, UVBR exclusion generally increased NO3−, NH4+, and urea uptakes. During the last 4 days of the experiment, the percent increase in the specific uptake rate of urea under excluded UVBR conditions varied between 17% and 130% and was a linear function of the ambient UVBR dose removed. During the first 3 days, the phytoplankton community dominated by diatoms was able to withstand UVBR enhancements without any perceptible effect on nitrogen uptake. However, during the post‐diatom bloom period, UVBR enhancements resulted in decreases in NO3−, NH4+, and urea uptake compared with ambient UVBR conditions. The reduction of urea uptake under UVBR enhancements during the last 3 days varied between 23% and 64% and was linearly related to the enhanced UVBR dose. However, the different UVBR treatments did not affect the internal organic nitrogen composition (internal urea, free amino acids, and proteins) of the phytoplankton community experiencing vertical mixing in the mesocosms. The discrepancy between short‐term uptake measurements at the surface and long‐term effects in the mesocosms emphasizes the importance of vertical mixing on UVBR effects in natural ecosystems. This suggests that an increase in ambient UVBR would have a minimal effect on nitrogen utilization by natural phytoplankton assemblages if these are vertically mixed.

UV Effects on Marine Planktonic Food Webs: A Synthesis of Results from Mesocosm Studies

Abstract UV irradiance has a broad range of effects on marine planktonic organisms. Direct and indirect effects on individual organisms have complex impacts on food-web structure and dynamics, with implications for carbon and nutrient cycling. Mesocosm experiments are well suited for the study of such complex interrelationships. Mesocosms offer the possibility to conduct well-controlled experiments with intact planktonic communities in physical, chemical and light conditions mimicking those of the natural environment. In allowing the manipulation of UV intensities and light spectral composition, the experimental mesocosm approach has proven to be especially useful in assessing the impacts at the community level. This review of mesocosm studies shows that, although a UV increase even well above natural intensities often has subtle effects on bulk biomass (carbon and chlorophyll), it can significantly impact the food-web structure because of different sensitivity to UV among planktonic organisms. Given the complexity of UV impacts, as evidenced by results of mesocosm studies, interactions between UV and changing environmental conditions (e.g. eutrophication and climate change) are likely to have significant effects on the function of marine ecosystems.

Geochemistry of ice-covered, meromictic Lake A in the Canadian High Arctic

The geochemical processes occurring within meromictic Lake A (maxdepth 120 m) on northern Ellesmere Island, Canada, were investigated to determinethe history of the lake and to provide a baseline for future studies. The lake contained seawaterdiluted by freshwater input that had been mixed prior to the lakes isolation from tidalaction. Input of freshwater after isolation of the lake created vertical stratification resultingin the creation of distinct oxic, suboxic and anoxic zones. Dissolved oxygen was present to 13 m,and sulphide beneath 32 m. Manganese and iron cycling dominated the redox chemistrybetween these depths. Total manganese concentrations reached 176 μM, higher thanin most other natural stratified lake or marine environments.

Effects of seston on ultraviolet attenuation in Lake Biwa

Abstract We examined the attenuation of underwater ultraviolet (UV) radiation and photosynthetically available radiation (PAR) in Lake Biwa, Japan, at offshore and inshore sites and under contrasting stratification and mixing regimes. There were large spatial differences in the water column transparency to both wavebands, despite little change in concentrations of dissolved organic carbon (DOC). The 1% of surface irradiance depth varied from 0.3 to 2.7 m at 305 nm, from 0.8 to 6.3 m at 380 nm, and from 2.3 to 12.8 m for PAR. Both PAR and UV transparency declined abruptly in the South Basin of the lake when a typhoon caused the resuspension of sediments. The water column ratio of UV to PAR increased by 30% at all stations over the course of a 3-week sampling period associated with the general increase in phytoplankton concentrations. At several sites, the diffuse attenuation coefficient for UV radiation deviated substantially from that predicted from UV-DOC models. A significantly positive linear relationship was found between UV attenuation (Kd determined with a profiling UV radiometer) and the beam attenuation coefficient at 660 nm as measured by transmissometer. These results indicate that scattering and absorption by particulate matter can reduce UV transparency to below that inferred from DOC concentrations, and that current UV-exposure models should be modified to incorporate this effect.

Alteration of shell nacre micromorphology in blue mussel Mytilus edulis after exposure to free-ionic silver and silver nanoparticles

This study describes the morphology of inner shell surface (ISS) of the blue mussel Mytilus edulis Linnaeus after short-term exposures to radiolabeled silver in free-ionic ((110m)Ag(+)) and engineered nanoparticulate ((110m)AgNPs, <40 nm) phases. Radiolabeled silver in starting solutions was used in a similar low concentration (∼15 Bq mL(-1)) for both treatments. After exposure experiments radiolabeled silver was leached from the ISS using HCl. It concentration for shells from both treatments was ∼0.5 Bq mL(-1). Whole ISS of young individuals and prismatic layer of adults showed no evidence of any major alteration process after silver uptake. However, the nacre portion of adult mussels exposed to both treatments revealed distinct doughnut shape structures (DSS) formed by calcium carbonate micrograins that covered the surface of aragonite tablets. Scanning electron microscope (SEM) imaging revealed the existence of only minor differences in DSS morphology between mussels exposed to Ag(+) and AgNPs. From literature survey, DSS were also found in bivalves exposed to Cd(2+). The DSS occurring in a specimen of a field-collected bivalve is also shown. Formation of distinctive DSS can be explained by a disturbance of the shell calcification mechanism. Although the occurrence of DSS is not exclusively associated with metal bioavailability to the mussels, the morphology of DSS seems to be linked to the speciation of the metal used in the uptake experiments.

Simulation of Ozone Depletion Using Ambient Irradiance Supplemented with UV Lamps

Abstract In studies of the biological effects of UV radiation, ozone depletion can be mimicked by performing the study under ambient conditions and adding radiation with UV-B lamps. We evaluated this methodology at three different locations along a latitudinal gradient: Rimouski (Canada), Ubatuba (Brazil) and Ushuaia (Argentina). Experiments of the effect of potential ozone depletion on marine ecosystems were carried out in large outdoor enclosures (mesocosms). In all locations we simulated irradiances corresponding to 60% ozone depletion, which may produce a 130–1900% increase in 305 nm irradiance at noon, depending on site and season. Supplementation with a fixed percentage of ambient irradiance provides a better simulation of irradiance increase due to ozone depletion than supplementation with a fixed irradiance value, particularly near sunrise and sunset or under cloudy skies. Calculations performed for Ushuaia showed that, on very cloudy days, supplementation by the square-wave method may produce unrealistic irradiances. Differences between the spectra of the calculated supplementing irradiance and the lamp for a given site and date will be a function of the time of day and may become more or less pronounced according to the biological weighting function of the effect under study.

First record of the green microalgae Coccomyxa sp. in blue mussel Mytilus edulis (L.) from the Lower St. Lawrence Estuary (Québec, Canada)

During autumn 2012 and spring 2013, blue mussels Mytilus edulis (L.) with strongly deformed (L-shaped) posterior shell margins and green spots in soft tissue (microalgae) were collected from intertidal zone along the south shore of the Lower St. Lawrence Estuary near Rimouski (Québec, Canada). Identification of algal cells infesting mussels as Coccomyxa sp. was confirmed by rRNA sequencing and HPLC pigment analysis. Flow cytometric analysis revealed the presence of algal cells in the hemolymph and extrapallial fluid in mussels with deformed and non-deformed shells; concentrations of algal cells were ranged from about 200mL(-1) in mussels with actually non-deformed shells to concentrations reaching up to 3.8×10(7)mL(-1) in mussels with heavily deformed ones. Chemical analyses of soft tissues led us to conclude that butyltin compounds and trace metals cannot be considered among factors responsible for the shell deformity observed. Using scanning electron microscopy, the biogenic nature of the erosion on the external shell surface and aragonitic lenses of prisms in the curvature zone of deformed shells (in sections) were recorded. The sequence of the green algae from M. edulis of the Lower St. Lawrence Estuary was closely related to Coccomyxa sp. infecting M. edulis from the Flensburg Fjord (North Sea) and Modiolus modiolus (L.) from the Vityaz Bay (Sea of Japan).

UV Effects on Aquatic Microbial Food Webs in Northern Lakes and Rivers

Lakes, ponds and rivers occur throughout the arctic and subarctic landscape and provide the habitat for a variety of aquatic life including zooplankton, insects, fish and birds. The base of the food webs supporting these animal populations is still poorly understood, but at many sites examined to date the biomass and energy flow in the lower food web is mostly associated with microscopic species of diverse nutritional modes: photosynthetic bacteria and micro-algae; heterotrophic and chemotrophic bacteria; phagotrophic flagellates, ciliates and amoeboid protozoa; parasitic organisms including viruses; and mixotrophic protists that can obtain their carbon and energy supply by heterotrophic processes as well as by photosynthesis. These organisms collectively form the microbial food web (Fig. 7.1) that recycles nutrients and passes on carbon and other elements to higher trophic levels. In deeper lakes and rivers this microbial community is mostly planktonic and is distributed throughout the water column In shallow-water systems, which are especially abundant throughout the North (e.g., thaw ponds on the tundra, polar desert streams), these diverse functional groups are most abundant in the benthic mats or films that form the periphyton over the surface of rocks, sediment and submerged plants such as aquatic mosses. Even in deeper lakes, the benthic microbial communities play a major role in biomass production and biogeochemical transformations.

Free-living stage of the unicellular algae Coccomyxa sp. parasite of the blue mussel (Mytilus edulis): Low-light adaptation, capacity for growth at a very wide salinity range and tolerance to low pH

Coccomyxa parasitica and similar, unidentified Coccomyxa species infect the soft tissues of many bivalve species, giving them a conspicuous green coloration and leading to mantle and shell deformities. Very little information exists regarding the ecophysiology of parasitic Coccomyxa sp. and this limits our ability to understand how it can achieve its unusual life history. In the present study, the growth of Coccomyxa sp. Metis-sur-mer (KJ372210) in liquid culture was investigated. Coccomyxa sp. maximum growth rate was 0.75 day-1 (equivalent to a doubling time of 22 hours), growth saturated at ∼100 μmol quanta m-2 s-1 and was still ∼20% of maximum at 13 μmol quanta m-2 s-1, the lowest photosynthetically available radiation (PAR) intensity tested. Coccomyxa sp. showed a very wide tolerance to salinity, with growth rate practically invariable over the salinity range 15-35. Even in natural spring water enriched with f/2 media, the growth rate was nearly half of maximum. Unlike the closely related acid-tolerant Coccomyxa sp. CPCC 508, Coccomyxa sp. Metis-sur-mer could not grow in acidic waters. Considering the ability of Coccomyxa sp. to achieve a high growth rate at low irradiance and its relative insensitivity to the prevailing salinity, it is somewhat surprising it has not yet infected bivalves at a larger scale worldwide.