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Papers by Gustavo Ferreyra

Journal of Experimental Marine Biology and Ecology, 2011

... Thumbnails - selected | Full-Size images. Article. Article - selected. Figures/Tables. Figure... more ... Thumbnails - selected | Full-Size images. Article. Article - selected. Figures/Tables. Figures/Tables - selected. References. References - selected. Journal of Experimental Marine Biology and Ecology Volume 406, Issues 1-2, 30 September 2011, Pages 95-107. ...

This article describes the use of group model building to facilitate interaction with stakeholder... more This article describes the use of group model building to facilitate interaction with stakeholders, synthesize research results and assist in the development of hypotheses about climate change at the global level in relation to UV-B radiation and ecosystem service valuation. The objective was to provide a platform for integration of the various research components within a multidisciplinary research project as a basis for interaction with stakeholders with backgrounds in areas other than science. An integrated summary of the scientific findings, along with stakeholder input, was intended to produce a bridge between science and policymaking. We used a mediated modeling approach that was implemented as a pilot project in Ushuaia, Argentina. The investigation was divided into two participatory workshops: data gathering and model evaluation. Scientists and the local stakeholders supported the valuation of ecosystem services as a useful common denominator for integrating the various scientific results. The concept of economic impacts in aquatic and marsh systems was represented by values for ecosystem services altered by UV-B radiation. In addition, direct local socioeconomic impacts of enhanced UV-B radiation were modeled, using data from Ushuaia. We worked with 5 global latitudinal regions, focusing on net primary production and biomass for the marine system and on 3 plant species for the marsh system. Ecosystem service values were calculated for both sectors. The synthesis model reflects the conclusions from the literature and from experimental research at the global level. UV-B is not a significant stress for the marshes, relative to the potential impact of increases in the sea level. Enhanced UV-B favors microbial dynamics in marine systems that could cause a significant shift from primary producers to bacteria at the community level. In addition, synergetic effects of UV-B and certain pollutants potentiate the shift to heterotrophs. This may impact the oceanic carbon cycle by increasing the ratio of respiratory to photosynthetic organisms in surface waters and, thus, the role of the ocean as a carbon sink for atmospheric CO 2 . In summary, although changes in the marine sector due to anthropogenic influences may affect global climate change, marshes are expected to primarily be affected by climate change.

Photochemistry and Photobiology, 2006

The studies on the effects of ultraviolet radiation (UVR, 240-400 nm) on bacteria and phytoplankt... more The studies on the effects of ultraviolet radiation (UVR, 240-400 nm) on bacteria and phytoplankton in Potter Cove started in 1988. A set of publications including PhD theses were produced, while other studies are still ongoing. Here we attempt to synthesize the knowledge gained on this subject along the years in an integral way, additionally including a brief description of the light field in Potter Cove waters. The different methods used to reach the results presented here can be found in the referenced papers

und Meeresforschung Am Handelshafen 12 -Geb. E 27570 Bremerhaven * This work is dedicated to the ... more und Meeresforschung Am Handelshafen 12 -Geb. E 27570 Bremerhaven * This work is dedicated to the memory of Augusto "Alfa" Thibaud and Teófilo González, who lost their lives in a glacier crevasse near Jubany during the overwintering in 2005.

Latin American Journal of Aquatic Research, 2011

In January 1999, unialgal cultures of the diatom Thalassiosira sp., solate from natural phytoplan... more In January 1999, unialgal cultures of the diatom Thalassiosira sp., solate from natural phytoplankton assemblages from Potter Cove, Antarctica, were exposed to solar ultraviolet radiation (UVR, in order to study the long-term acclimation of this species. Ultraviolet radiation B (UVBR, 280-315 nm) inhibited the growth rate during the first and second days of exposure. No UVBR inhibition was observed on the third day. The initial content of α-tocopherol (13 pmol (10 4 cell) -1 ) showed a marked decrease during the exponential growth phase (4 pmol (10 4 cell -1 ) by day 3). The initial content of β-carotene (3 pmol (10 4 cell) -1 ) did not show significant differences over time in cells exposed to UVBR. Two mycosporine-like amino acids (MAAs) were identified: porphyra-334 and shinorine. Cellular concentrations of MAAs increased significantly on days 2 and 3, and exposure of the algae to UVBR significantly enhanced this value. The relative importance of MAAs concentration was significant (P < 0.05) in relation to the α-tocopherol content. A positive correlation was shown between cellular MAAs concentration and growth rate. Our results suggest that photoprotection against UV-induced damage is characterized by short-term consumption of α-tocopherol and longer-term synthesis of MAAs. The UVBR damage/repair ratio during long-term exposure involves the combined action of several endogenous factors within the cell, with MAAs synthesis being the most effective factor related to photoprotection.

Polar Biology, 2011

Among the few existing works on seasonal variation in metabolic rate of polar species, most have ... more Among the few existing works on seasonal variation in metabolic rate of polar species, most have been conducted during summer due to logistic constraints and have been focused on species that cease feeding during winter. In this work, we present the Wrst extensive data set on the seasonal variation in metabolic rate of G. antarctica, an abundant amphipod that feeds throughout the year, and its relationship with body size, potential food availability and temperature. We measured the resting metabolic rate (RMR) of groups of individuals during 6 months from late summer through winter at 4 experimental temperatures and for a wide range of body size. RMR had a negative allometric scaling with body size and showed a tendency to increase with temperature as expected. However, temperature and body size eVects on RMR showed a signiWcant temporal variation, and an increase in temperature decreased scaling exponents. RMR at the mean seawater temperature throughout the study showed a strong seasonal variation following food availability: RMR decreased from the end of summer through winter, coinciding with a reduction in microphytobenthos stock, but recovered summer values in August, when an epontic algae boom occurred. The seasonal factorial aerobic scope (£2.37) is lower than benthic Antarctic invertebrates that cease feeding during winter, in agreement with what is expected based on theoretical grounds. Results suggest that seasonal variation of RMR would allow G. antarctica to achieve a high eYciency in energy utilization, while maintaining the ability to exploit sudden changes in food supply.

Photochemistry and Photobiology, 2006

We present a mathematical model for a phytoplanktonzooplankton system, based on a predator-prey s... more We present a mathematical model for a phytoplanktonzooplankton system, based on a predator-prey scheme. The model considers the effects of sinking in the phytoplankton, vertical mixing and attenuation of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) in the water column. In a first approach, the model was studied under conditions of average PAR irradiance and shows fluctuations and stable equilibrium points. Secondly, we introduced the effects of photoperiod and photoinhibition by UVR and vertical mixing. Under these conditions, the phytoplankton biomass oscillates depending on the combined effects of UVR and mixing. Higher inhibition by UVR and longer mixing periods can induce strong fluctuations in the system but can also produce higher plankton peaks.

VertigO, 2004

ABSTRACT Seasonal ice cover is linked to an intense biological activity in polar regions. Every y... more ABSTRACT Seasonal ice cover is linked to an intense biological activity in polar regions. Every year, ice melting induces the stabilisation of the water column which can be observed until 150 km from the margin of seasonal ice, favoring the development of profuse phytoplankton blooms. For the case of Antarctica, life cycles of key species in the ecosystem, particularly the krill Euphausia superba, strongly depends on ice dynamics. This species has been considered as the main link between phytoplankton and higher trophic levels in the food web (fishes, birds and mammals). Several field observations as well as models suggest a replacement of krill by another group of organisms: the salps (particularly Salpa thompsoni). Such replacement has been related to the decrease in duration and extent of seasonal ice during the last decades, which in turn shows a strong correlation with the air temperature increase in some areas of Antarctica (Amundsen – Bellingshausen seas and Antarctic Peninsula). These changes could have significant consequences for both the biodiversity and the functioning of the Antarctic ecosystem, since salps represent a low energy source for high predators. The potential significance of the above processes on Antarctic ecosystem dynamics is analysed in the present paper.

Polar Research, 2009

The effect of UVR on the viability of the culturable bacterial community fraction (CBC), and two ... more The effect of UVR on the viability of the culturable bacterial community fraction (CBC), and two of their isolated components (Arthrobacter-UVvi and Bizionia-UVps), was studied in the top few metres of the water column at Potter Cove, King George Island, Antarctica. Quartz flasks containing CBC from surface waters were exposed to solar radiation at depths of 0, 1 and 3 m. Similar experiments using UVps and UVvi isolates were performed. In some experiments interferential filters were used to discriminate photosynthetic active radiation (PAR), UV-A and UV-B. CBC from depths of 0, 10 and 30 m were also exposed to surface solar radiation. The deleterious effect of UVR was observed at the surface and at a depth of 1 m, but not at a depth of 3 m. Studies with interferential filters showed low bacterial viability values at depths of 0 and 1 m under both UVR treatments. However, under low radiation doses the effect attributed to UV-B was higher than that caused by UV-A. The surface CBC was more resistant to UVR compared with CBC from a depth of 30 m. The results showed that CBC inhabiting waters above the pycnocline (located at a depth of 5-10 m) are more efficiently adapted to UVR than are those from below the pycnocline. The impact of UVR on the marine bacterioplankton studied was only detected in the first metre of the stratified water column of Potter Cove, which has high levels of suspended particulate matter. These results support the evidence for a significant UVR-attenuating effect in the water column of this coastal Antarctic water.

Polar Biology, 2005

Page 1. ORIGINAL PAPER Jose´e Nina Bouchard Æ Suzanne Roy Æ Gustavo Ferreyra Douglas A. Campbell ... more Page 1. ORIGINAL PAPER Jose´e Nina Bouchard Æ Suzanne Roy Æ Gustavo Ferreyra Douglas A. Campbell Æ Antonio Curtosi Ultraviolet-B effects on photosystem II efficiency of natural phytoplankton communities from Antarctica ...

Polar Biology, 2010

Although winter conditions play a major role in determining the productivity of the western Antar... more Although winter conditions play a major role in determining the productivity of the western Antarctic Peninsula (WAP) waters for the following spring and summer, a few studies have dealt with the seasonal variability of microorganisms in the WAP in winter. Moreover, because of regional warming, sea-ice retreat is happening earlier in spring, at the onset of the production season. In this context, this study describes the dynamics of the marine microbial community in the Melchior Archipelago (WAP) from fall to spring 2006. Samples were collected monthly to biweekly at four depths from the surface to the aphotic layer. The abundance and carbon content of bacteria, phytoplankton and microzooplankton were analyzed using flow cytometry and inverted microscopy, and bacterial richness was examined by PCR-DGGE. As expected, due to the extreme environmental conditions, the microbial community abundance and biomass were low in fall and winter. Bacterial abundance ranged from 1.2 to 2.8 9 10 5 cells ml -1 showing a slight increase in spring. Phytoplankton biomass was low and dominated by small cells (\2 lm) in fall and winter (average chlorophyll a concentration, Chl-a, of, respectively, 0.3 and 0.13 lg l -1 ). Phytoplankton biomass increased in spring (Chl-a up to 1.13 lg l -1 ), and, despite potentially adequate growth conditions, this rise was small and phytoplankton was still dominated by small cells (2-20 lm). In addition, the early disappearing of sea-ice in spring 2006 let the surface water exposed to ultraviolet B radiations (UVBR, 280-320 nm), which seemed to have a negative impact on the microbial community in surface waters.

Polar Biology, 2008

... Table 3 Environmental conditions recorded during peak abundances of Pseudo-nitzschia species ... more ... Table 3 Environmental conditions recorded during peak abundances of Pseudo-nitzschia species in the Weddell Sea Species Highest density (cells l–1) Station Temperature (°C) Salinity (Psu) NO2 – + NO3 – (μm) PO4 3– (μm) SiO3 2– (μm) ...

Polar Biology, 2002

Phytoplankton photosynthesis was measured during spring±summer 1991±1992 in the inner and outer p... more Phytoplankton photosynthesis was measured during spring±summer 1991±1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quanti®ed by means of the root-mean square expected vertical displacement depth of cells in the water column, Z t . The light attenuation coecient was used as a measure of the in¯uence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious dierences between photosynthetic capacity [P* max ; averages 2.6 and 0.6 lg C (lg chlorophyll-a) ±1 h ±1 ] and photosynthetic eciency {a*; 0.073 and 0.0018 lg C (lg chlorophyll-a) ±1 h ±1 [(lmol m ±2 s ±1 ) ±1 ]} values were obtained for both sites during low mixing conditions (Z t from 10 to 20 m), while no dierences were found for high mixing situations (Z t >20 m). This suggests dierent photoacclimation of phytoplankton responses, induced by modi®cations of the light ®eld, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P* max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area.

Photochemistry and Photobiology, 2006

This article describes the use of group model building to facilitate interaction with stakeholder... more This article describes the use of group model building to facilitate interaction with stakeholders, synthesize research results and assist in the development of hypotheses about climate change at the global level in relation to UV-B radiation and ecosystem service valuation. The objective was to provide a platform for integration of the various research components within a multidisciplinary research project as a basis for interaction with stakeholders with backgrounds in areas other than science. An integrated summary of the scientific findings, along with stakeholder input, was intended to produce a bridge between science and policymaking. We used a mediated modeling approach that was implemented as a pilot project in Ushuaia, Argentina. The investigation was divided into two participatory workshops: data gathering and model evaluation. Scientists and the local stakeholders supported the valuation of ecosystem services as a useful common denominator for integrating the various scientific results. The concept of economic impacts in aquatic and marsh systems was represented by values for ecosystem services altered by UV-B radiation. In addition, direct local socioeconomic impacts of enhanced UV-B radiation were modeled, using data from Ushuaia. We worked with 5 global latitudinal regions, focusing on net primary production and biomass for the marine system and on 3 plant species for the marsh system. Ecosystem service values were calculated for both sectors. The synthesis model reflects the conclusions from the literature and from experimental research at the global level. UV-B is not a significant stress for the marshes, relative to the potential impact of increases in the sea level. Enhanced UV-B favors microbial dynamics in marine systems that could cause a significant shift from primary producers to bacteria at the community level. In addition, synergetic effects of UV-B and certain pollutants potentiate the shift to heterotrophs. This may impact the oceanic carbon cycle by increasing the ratio of respiratory to photosynthetic organisms in surface waters and, thus, the role of the ocean as a carbon sink for atmospheric CO 2 . In summary, although changes in the marine sector due to anthropogenic influences may affect global climate change, marshes are expected to primarily be affected by climate change.

Photochemistry and Photobiology, 2006

Solar UVB radiation (280-320 nm) is known to have detrimental effects on marine phytoplankton. As... more Solar UVB radiation (280-320 nm) is known to have detrimental effects on marine phytoplankton. Associated with the seasonal ozone hole in Antarctica, stratospheric ozone depletion occasionally influences the sub-Antarctic (Beagle Channel, Argentina) region, enhancing levels of UVB. The primary objective of this work was to study the effects of several (i.e. 6-10) days of exposure to UVB on the taxonomic composition and photosynthetic inhibition of local phytoplankton communities. For different light treatments, fixeddepth incubations placed in an outdoors water tank were compared with incubations in 1900 L mesocosms, where vertical mixing was present. Phytoplankton growth was inhibited by UV radiation (UVR) in fixed-depth experiments but not in the mixed mesocosms. Under fixed and mixed conditions alike, photosynthesis was significantly inhibited by UVB at the beginning of the experiment but no longer after several days of exposure, suggesting that cells had acclimated to radiation conditions. There was a change in species composition in response to UVR exposure in both experiments, which likely explained acclimation. In the community exposed to fixed conditions this change was from a phytoflagellatedominated assemblage to a community with high relative abundance of diatoms after 6 days of exposure. UVA was responsible for most of the observed growth inhibition; however, the reduction in photosynthesis was produced by UVB. The reasons behind this variability in responses to UVR are associated with species-specific sensitivity and acclimation, and the previous light history of cells. In the community exposed in mesocosms, an assemblage codominated by phytoflagellates and diatoms was observed at the beginning of the experiments. After 10 days of exposure, green algae (Eutreptiella sp.) had increased, and phytoflagellates were the dominant group. The synthesis of mycosporine-like amino acids (MAAs), antioxidant enzymes and photosynthetic antenna pigments, in relation to repair and protection processes, may explain the reduced inhibition of both growth and photosynthesis that was observed in the phytoplankton community after several days of exposure. For environments such as the Beagle Channel seasonally exposed to the ozone hole, the results obtained from the fixed-depth experiments show that species can cope with UVR by means of MAA synthesis, while mixing would primarily promote a change in species composition and defense strategies.

Photochemistry and Photobiology, 2006

In studies of the biological effects of UV radiation, ozone depletion can be mimicked by performi... more 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.

Photochemistry and Photobiology, 2006

The impact of UV-B radiation (UVBR; 280-320 nm) on lower levels of a natural plankton assemblage ... more The impact of UV-B radiation (UVBR; 280-320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (~70-80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the lessaffected species (50% reduction in the H treatment compared with that of the N control), contrasting with~90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed.

Photochemistry and Photobiology, 2006

The effect of UVB radiation (UVBR, 290-320 nm) on the dynamics of the lower levels of the marine ... more The effect of UVB radiation (UVBR, 290-320 nm) on the dynamics of the lower levels of the marine plankton community was modeled. The model was built using differential equations and shows a good fit to experimental data collected in mesocosms (defined as large enclosures of 1500 L filled with natural marine waters). Some unexpected results appear to be possible by indirect effects in prey (bacteria, phytoplankton and heterotrophic flagellates). In particular, apparent competition appears between small phytoplankton and bacteria. This effect is caused by a shared predator (ciliates). Another remarkable effect is an increase in bacteria and flagellates populations due to enhanced UVBR. This effect is similar to that observed under mesocosm experimental conditions and is related to the decrease of predation due to the direct damage to predators (ciliates) by UVBR. The effect of UVBR changing interaction coefficients may be dramatic on the community structure, producing big changes in equilibrium populations, as demonstrated by sensitivity analysis of the model. In order to generalize these results to field conditions it will be necessary to increase model complexity and include extra organic mater sources, mixing and sinking effects and predation by large zooplankton. This work shows that UVBR may produce community global responses that are consequence of both direct and indirect effects among populations.

Journal of Experimental Marine Biology and Ecology, 2011

... Thumbnails - selected | Full-Size images. Article. Article - selected. Figures/Tables. Figure... more ... Thumbnails - selected | Full-Size images. Article. Article - selected. Figures/Tables. Figures/Tables - selected. References. References - selected. Journal of Experimental Marine Biology and Ecology Volume 406, Issues 1-2, 30 September 2011, Pages 95-107. ...

This article describes the use of group model building to facilitate interaction with stakeholder... more This article describes the use of group model building to facilitate interaction with stakeholders, synthesize research results and assist in the development of hypotheses about climate change at the global level in relation to UV-B radiation and ecosystem service valuation. The objective was to provide a platform for integration of the various research components within a multidisciplinary research project as a basis for interaction with stakeholders with backgrounds in areas other than science. An integrated summary of the scientific findings, along with stakeholder input, was intended to produce a bridge between science and policymaking. We used a mediated modeling approach that was implemented as a pilot project in Ushuaia, Argentina. The investigation was divided into two participatory workshops: data gathering and model evaluation. Scientists and the local stakeholders supported the valuation of ecosystem services as a useful common denominator for integrating the various scientific results. The concept of economic impacts in aquatic and marsh systems was represented by values for ecosystem services altered by UV-B radiation. In addition, direct local socioeconomic impacts of enhanced UV-B radiation were modeled, using data from Ushuaia. We worked with 5 global latitudinal regions, focusing on net primary production and biomass for the marine system and on 3 plant species for the marsh system. Ecosystem service values were calculated for both sectors. The synthesis model reflects the conclusions from the literature and from experimental research at the global level. UV-B is not a significant stress for the marshes, relative to the potential impact of increases in the sea level. Enhanced UV-B favors microbial dynamics in marine systems that could cause a significant shift from primary producers to bacteria at the community level. In addition, synergetic effects of UV-B and certain pollutants potentiate the shift to heterotrophs. This may impact the oceanic carbon cycle by increasing the ratio of respiratory to photosynthetic organisms in surface waters and, thus, the role of the ocean as a carbon sink for atmospheric CO 2 . In summary, although changes in the marine sector due to anthropogenic influences may affect global climate change, marshes are expected to primarily be affected by climate change.

Photochemistry and Photobiology, 2006

The studies on the effects of ultraviolet radiation (UVR, 240-400 nm) on bacteria and phytoplankt... more The studies on the effects of ultraviolet radiation (UVR, 240-400 nm) on bacteria and phytoplankton in Potter Cove started in 1988. A set of publications including PhD theses were produced, while other studies are still ongoing. Here we attempt to synthesize the knowledge gained on this subject along the years in an integral way, additionally including a brief description of the light field in Potter Cove waters. The different methods used to reach the results presented here can be found in the referenced papers

und Meeresforschung Am Handelshafen 12 -Geb. E 27570 Bremerhaven * This work is dedicated to the ... more und Meeresforschung Am Handelshafen 12 -Geb. E 27570 Bremerhaven * This work is dedicated to the memory of Augusto "Alfa" Thibaud and Teófilo González, who lost their lives in a glacier crevasse near Jubany during the overwintering in 2005.

Latin American Journal of Aquatic Research, 2011

In January 1999, unialgal cultures of the diatom Thalassiosira sp., solate from natural phytoplan... more In January 1999, unialgal cultures of the diatom Thalassiosira sp., solate from natural phytoplankton assemblages from Potter Cove, Antarctica, were exposed to solar ultraviolet radiation (UVR, in order to study the long-term acclimation of this species. Ultraviolet radiation B (UVBR, 280-315 nm) inhibited the growth rate during the first and second days of exposure. No UVBR inhibition was observed on the third day. The initial content of α-tocopherol (13 pmol (10 4 cell) -1 ) showed a marked decrease during the exponential growth phase (4 pmol (10 4 cell -1 ) by day 3). The initial content of β-carotene (3 pmol (10 4 cell) -1 ) did not show significant differences over time in cells exposed to UVBR. Two mycosporine-like amino acids (MAAs) were identified: porphyra-334 and shinorine. Cellular concentrations of MAAs increased significantly on days 2 and 3, and exposure of the algae to UVBR significantly enhanced this value. The relative importance of MAAs concentration was significant (P < 0.05) in relation to the α-tocopherol content. A positive correlation was shown between cellular MAAs concentration and growth rate. Our results suggest that photoprotection against UV-induced damage is characterized by short-term consumption of α-tocopherol and longer-term synthesis of MAAs. The UVBR damage/repair ratio during long-term exposure involves the combined action of several endogenous factors within the cell, with MAAs synthesis being the most effective factor related to photoprotection.

Polar Biology, 2011

Among the few existing works on seasonal variation in metabolic rate of polar species, most have ... more Among the few existing works on seasonal variation in metabolic rate of polar species, most have been conducted during summer due to logistic constraints and have been focused on species that cease feeding during winter. In this work, we present the Wrst extensive data set on the seasonal variation in metabolic rate of G. antarctica, an abundant amphipod that feeds throughout the year, and its relationship with body size, potential food availability and temperature. We measured the resting metabolic rate (RMR) of groups of individuals during 6 months from late summer through winter at 4 experimental temperatures and for a wide range of body size. RMR had a negative allometric scaling with body size and showed a tendency to increase with temperature as expected. However, temperature and body size eVects on RMR showed a signiWcant temporal variation, and an increase in temperature decreased scaling exponents. RMR at the mean seawater temperature throughout the study showed a strong seasonal variation following food availability: RMR decreased from the end of summer through winter, coinciding with a reduction in microphytobenthos stock, but recovered summer values in August, when an epontic algae boom occurred. The seasonal factorial aerobic scope (£2.37) is lower than benthic Antarctic invertebrates that cease feeding during winter, in agreement with what is expected based on theoretical grounds. Results suggest that seasonal variation of RMR would allow G. antarctica to achieve a high eYciency in energy utilization, while maintaining the ability to exploit sudden changes in food supply.

Photochemistry and Photobiology, 2006

We present a mathematical model for a phytoplanktonzooplankton system, based on a predator-prey s... more We present a mathematical model for a phytoplanktonzooplankton system, based on a predator-prey scheme. The model considers the effects of sinking in the phytoplankton, vertical mixing and attenuation of photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) in the water column. In a first approach, the model was studied under conditions of average PAR irradiance and shows fluctuations and stable equilibrium points. Secondly, we introduced the effects of photoperiod and photoinhibition by UVR and vertical mixing. Under these conditions, the phytoplankton biomass oscillates depending on the combined effects of UVR and mixing. Higher inhibition by UVR and longer mixing periods can induce strong fluctuations in the system but can also produce higher plankton peaks.

VertigO, 2004

ABSTRACT Seasonal ice cover is linked to an intense biological activity in polar regions. Every y... more ABSTRACT Seasonal ice cover is linked to an intense biological activity in polar regions. Every year, ice melting induces the stabilisation of the water column which can be observed until 150 km from the margin of seasonal ice, favoring the development of profuse phytoplankton blooms. For the case of Antarctica, life cycles of key species in the ecosystem, particularly the krill Euphausia superba, strongly depends on ice dynamics. This species has been considered as the main link between phytoplankton and higher trophic levels in the food web (fishes, birds and mammals). Several field observations as well as models suggest a replacement of krill by another group of organisms: the salps (particularly Salpa thompsoni). Such replacement has been related to the decrease in duration and extent of seasonal ice during the last decades, which in turn shows a strong correlation with the air temperature increase in some areas of Antarctica (Amundsen – Bellingshausen seas and Antarctic Peninsula). These changes could have significant consequences for both the biodiversity and the functioning of the Antarctic ecosystem, since salps represent a low energy source for high predators. The potential significance of the above processes on Antarctic ecosystem dynamics is analysed in the present paper.

Polar Research, 2009

The effect of UVR on the viability of the culturable bacterial community fraction (CBC), and two ... more The effect of UVR on the viability of the culturable bacterial community fraction (CBC), and two of their isolated components (Arthrobacter-UVvi and Bizionia-UVps), was studied in the top few metres of the water column at Potter Cove, King George Island, Antarctica. Quartz flasks containing CBC from surface waters were exposed to solar radiation at depths of 0, 1 and 3 m. Similar experiments using UVps and UVvi isolates were performed. In some experiments interferential filters were used to discriminate photosynthetic active radiation (PAR), UV-A and UV-B. CBC from depths of 0, 10 and 30 m were also exposed to surface solar radiation. The deleterious effect of UVR was observed at the surface and at a depth of 1 m, but not at a depth of 3 m. Studies with interferential filters showed low bacterial viability values at depths of 0 and 1 m under both UVR treatments. However, under low radiation doses the effect attributed to UV-B was higher than that caused by UV-A. The surface CBC was more resistant to UVR compared with CBC from a depth of 30 m. The results showed that CBC inhabiting waters above the pycnocline (located at a depth of 5-10 m) are more efficiently adapted to UVR than are those from below the pycnocline. The impact of UVR on the marine bacterioplankton studied was only detected in the first metre of the stratified water column of Potter Cove, which has high levels of suspended particulate matter. These results support the evidence for a significant UVR-attenuating effect in the water column of this coastal Antarctic water.

Polar Biology, 2005

Page 1. ORIGINAL PAPER Jose´e Nina Bouchard Æ Suzanne Roy Æ Gustavo Ferreyra Douglas A. Campbell ... more Page 1. ORIGINAL PAPER Jose´e Nina Bouchard Æ Suzanne Roy Æ Gustavo Ferreyra Douglas A. Campbell Æ Antonio Curtosi Ultraviolet-B effects on photosystem II efficiency of natural phytoplankton communities from Antarctica ...

Polar Biology, 2010

Although winter conditions play a major role in determining the productivity of the western Antar... more Although winter conditions play a major role in determining the productivity of the western Antarctic Peninsula (WAP) waters for the following spring and summer, a few studies have dealt with the seasonal variability of microorganisms in the WAP in winter. Moreover, because of regional warming, sea-ice retreat is happening earlier in spring, at the onset of the production season. In this context, this study describes the dynamics of the marine microbial community in the Melchior Archipelago (WAP) from fall to spring 2006. Samples were collected monthly to biweekly at four depths from the surface to the aphotic layer. The abundance and carbon content of bacteria, phytoplankton and microzooplankton were analyzed using flow cytometry and inverted microscopy, and bacterial richness was examined by PCR-DGGE. As expected, due to the extreme environmental conditions, the microbial community abundance and biomass were low in fall and winter. Bacterial abundance ranged from 1.2 to 2.8 9 10 5 cells ml -1 showing a slight increase in spring. Phytoplankton biomass was low and dominated by small cells (\2 lm) in fall and winter (average chlorophyll a concentration, Chl-a, of, respectively, 0.3 and 0.13 lg l -1 ). Phytoplankton biomass increased in spring (Chl-a up to 1.13 lg l -1 ), and, despite potentially adequate growth conditions, this rise was small and phytoplankton was still dominated by small cells (2-20 lm). In addition, the early disappearing of sea-ice in spring 2006 let the surface water exposed to ultraviolet B radiations (UVBR, 280-320 nm), which seemed to have a negative impact on the microbial community in surface waters.

Polar Biology, 2008

... Table 3 Environmental conditions recorded during peak abundances of Pseudo-nitzschia species ... more ... Table 3 Environmental conditions recorded during peak abundances of Pseudo-nitzschia species in the Weddell Sea Species Highest density (cells l–1) Station Temperature (°C) Salinity (Psu) NO2 – + NO3 – (μm) PO4 3– (μm) SiO3 2– (μm) ...

Polar Biology, 2002

Phytoplankton photosynthesis was measured during spring±summer 1991±1992 in the inner and outer p... more Phytoplankton photosynthesis was measured during spring±summer 1991±1992 in the inner and outer part of the shallow Potter Cove, King George Island. Strong winds characterise this area. Wind-induced turbulent mixing was quanti®ed by means of the root-mean square expected vertical displacement depth of cells in the water column, Z t . The light attenuation coecient was used as a measure of the in¯uence of the large amount of terrigenous particles usually present in the water column; 1% light penetration ranged between 30 and 9 m, and between 30 and 15 m for the inner and outer cove, respectively. Obvious dierences between photosynthetic capacity [P* max ; averages 2.6 and 0.6 lg C (lg chlorophyll-a) ±1 h ±1 ] and photosynthetic eciency {a*; 0.073 and 0.0018 lg C (lg chlorophyll-a) ±1 h ±1 [(lmol m ±2 s ±1 ) ±1 ]} values were obtained for both sites during low mixing conditions (Z t from 10 to 20 m), while no dierences were found for high mixing situations (Z t >20 m). This suggests dierent photoacclimation of phytoplankton responses, induced by modi®cations of the light ®eld, which in turn are controlled by physical forcing. Our results suggest that although in experimental work P* max can be high, wind-induced mixing and low irradiance will prevent profuse phytoplankton development in the area.

Photochemistry and Photobiology, 2006

This article describes the use of group model building to facilitate interaction with stakeholder... more This article describes the use of group model building to facilitate interaction with stakeholders, synthesize research results and assist in the development of hypotheses about climate change at the global level in relation to UV-B radiation and ecosystem service valuation. The objective was to provide a platform for integration of the various research components within a multidisciplinary research project as a basis for interaction with stakeholders with backgrounds in areas other than science. An integrated summary of the scientific findings, along with stakeholder input, was intended to produce a bridge between science and policymaking. We used a mediated modeling approach that was implemented as a pilot project in Ushuaia, Argentina. The investigation was divided into two participatory workshops: data gathering and model evaluation. Scientists and the local stakeholders supported the valuation of ecosystem services as a useful common denominator for integrating the various scientific results. The concept of economic impacts in aquatic and marsh systems was represented by values for ecosystem services altered by UV-B radiation. In addition, direct local socioeconomic impacts of enhanced UV-B radiation were modeled, using data from Ushuaia. We worked with 5 global latitudinal regions, focusing on net primary production and biomass for the marine system and on 3 plant species for the marsh system. Ecosystem service values were calculated for both sectors. The synthesis model reflects the conclusions from the literature and from experimental research at the global level. UV-B is not a significant stress for the marshes, relative to the potential impact of increases in the sea level. Enhanced UV-B favors microbial dynamics in marine systems that could cause a significant shift from primary producers to bacteria at the community level. In addition, synergetic effects of UV-B and certain pollutants potentiate the shift to heterotrophs. This may impact the oceanic carbon cycle by increasing the ratio of respiratory to photosynthetic organisms in surface waters and, thus, the role of the ocean as a carbon sink for atmospheric CO 2 . In summary, although changes in the marine sector due to anthropogenic influences may affect global climate change, marshes are expected to primarily be affected by climate change.

Photochemistry and Photobiology, 2006

Solar UVB radiation (280-320 nm) is known to have detrimental effects on marine phytoplankton. As... more Solar UVB radiation (280-320 nm) is known to have detrimental effects on marine phytoplankton. Associated with the seasonal ozone hole in Antarctica, stratospheric ozone depletion occasionally influences the sub-Antarctic (Beagle Channel, Argentina) region, enhancing levels of UVB. The primary objective of this work was to study the effects of several (i.e. 6-10) days of exposure to UVB on the taxonomic composition and photosynthetic inhibition of local phytoplankton communities. For different light treatments, fixeddepth incubations placed in an outdoors water tank were compared with incubations in 1900 L mesocosms, where vertical mixing was present. Phytoplankton growth was inhibited by UV radiation (UVR) in fixed-depth experiments but not in the mixed mesocosms. Under fixed and mixed conditions alike, photosynthesis was significantly inhibited by UVB at the beginning of the experiment but no longer after several days of exposure, suggesting that cells had acclimated to radiation conditions. There was a change in species composition in response to UVR exposure in both experiments, which likely explained acclimation. In the community exposed to fixed conditions this change was from a phytoflagellatedominated assemblage to a community with high relative abundance of diatoms after 6 days of exposure. UVA was responsible for most of the observed growth inhibition; however, the reduction in photosynthesis was produced by UVB. The reasons behind this variability in responses to UVR are associated with species-specific sensitivity and acclimation, and the previous light history of cells. In the community exposed in mesocosms, an assemblage codominated by phytoflagellates and diatoms was observed at the beginning of the experiments. After 10 days of exposure, green algae (Eutreptiella sp.) had increased, and phytoflagellates were the dominant group. The synthesis of mycosporine-like amino acids (MAAs), antioxidant enzymes and photosynthetic antenna pigments, in relation to repair and protection processes, may explain the reduced inhibition of both growth and photosynthesis that was observed in the phytoplankton community after several days of exposure. For environments such as the Beagle Channel seasonally exposed to the ozone hole, the results obtained from the fixed-depth experiments show that species can cope with UVR by means of MAA synthesis, while mixing would primarily promote a change in species composition and defense strategies.

Photochemistry and Photobiology, 2006

In studies of the biological effects of UV radiation, ozone depletion can be mimicked by performi... more 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.

Photochemistry and Photobiology, 2006

The impact of UV-B radiation (UVBR; 280-320 nm) on lower levels of a natural plankton assemblage ... more The impact of UV-B radiation (UVBR; 280-320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (~70-80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the lessaffected species (50% reduction in the H treatment compared with that of the N control), contrasting with~90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed.

Photochemistry and Photobiology, 2006

The effect of UVB radiation (UVBR, 290-320 nm) on the dynamics of the lower levels of the marine ... more The effect of UVB radiation (UVBR, 290-320 nm) on the dynamics of the lower levels of the marine plankton community was modeled. The model was built using differential equations and shows a good fit to experimental data collected in mesocosms (defined as large enclosures of 1500 L filled with natural marine waters). Some unexpected results appear to be possible by indirect effects in prey (bacteria, phytoplankton and heterotrophic flagellates). In particular, apparent competition appears between small phytoplankton and bacteria. This effect is caused by a shared predator (ciliates). Another remarkable effect is an increase in bacteria and flagellates populations due to enhanced UVBR. This effect is similar to that observed under mesocosm experimental conditions and is related to the decrease of predation due to the direct damage to predators (ciliates) by UVBR. The effect of UVBR changing interaction coefficients may be dramatic on the community structure, producing big changes in equilibrium populations, as demonstrated by sensitivity analysis of the model. In order to generalize these results to field conditions it will be necessary to increase model complexity and include extra organic mater sources, mixing and sinking effects and predation by large zooplankton. This work shows that UVBR may produce community global responses that are consequence of both direct and indirect effects among populations.