Phytoplankton cell death induced by solar ultraviolet radiation

En esta tesis se ha demostrado que la radiación ultravioleta induce mortalidad en comunidades de fitoplancton de diferentes áreas del Océano Atlántico, del Mar Mediterráneo y del Océano Antártico. El fitoplancton más pequeño (pico-fitoplancton) muestra mayor sensibilidad a la radiación UV respecto al fitoplancton de mayor tamaño. Este estudio identifica que el crecimiento de las poblaciones del fitoplancton antártico está controlado por la radiación ultravioleta con inhibiciones de biomasas por encima del 80-90%. Se demuestra también que la transferencia de radicales OH, generados por la radiación ultravioleta, desde la atmósfera hacia la superficie del Océano causa mortalidad en comunidades de fitoplancton de aguas tropicales, templadas y antárticas. El trabajo presentado en esta tesis muestra la importancia de la radiación ultravioleta como factor que induce mortalidad en el fitoplancton, su influencia en el balance del crecimiento neto de estas poblaciones, así como las consecuencias que se derivan en la cadena trófica

Phytoplankton cell death induced by solar ultraviolet radiation

En esta tesis se ha demostrado que la radiación ultravioleta induce mortalidad en comunidades de fitoplancton de diferentes áreas del Océano Atlántico, del Mar Mediterráneo y del Océano Antártico. El fitoplancton más pequeño (pico-fitoplancton) muestra mayor sensibilidad a la radiación UV respecto al fitoplancton de mayor tamaño. Este estudio identifica que el crecimiento de las poblaciones del fitoplancton antártico está controlado por la radiación ultravioleta con inhibiciones de biomasas por encima del 80-90%. Se demuestra también que la transferencia de radicales OH, generados por la radiación ultravioleta, desde la atmósfera hacia la superficie del Océano causa mortalidad en comunidades de fitoplancton de aguas tropicales, templadas y antárticas. El trabajo presentado en esta tesis muestra la importancia de la radiación ultravioleta como factor que induce mortalidad en el fitoplancton, su influencia en el balance del crecimiento neto de estas poblaciones, así como las consecuencias que se derivan en la cadena trófica

Effects of ultraviolet radiation on growth, cell death and the standing stock of Antarctic phytoplankton

10 páginas, 5 figuras, 1 tabla. -- Artículo Open Access.We performed a series of experiments with Antarctic natural phytoplankton communities exposed to natural levels of solar radiation in order to quantify the effect of ambient ultraviolet radiation (UVR) on phytoplankton growth, cell death and their balance. Treatments in which UVR was excluded showed a high increase in biomass, dominated by diatoms, with chl a (chlorophyll a) reaching values as high as 22 µg l–1, 9 times larger than initial values. In contrast, chl a values remained low at the end of the experiments under treatments with full solar radiation. Phytoplankton growth rates were also inhibited by UVR, increasing up to 5 times in UVR-excluded treatments. The percentage of dead cells within Antarctic phytoplankton communities decreased in treatments with UVR blocked. The Antarctic phytoplankton populations studied appeared to be strongly controlled by UV at surface irradiances with biomasses inhibited by up to 80–90%. This suggests that increased UVR levels over Antarctica may reduce phytoplankton growth rates and cause cell death, thus reducing the phytoplankton stock. These effects may have important consequences for the food web in Antarctic waters.Este trabajo es una contribución al proyecto ICEPOS (REN2002-04165-C03-02/ANT) financiado por el Ministerio español de Educación y Ciencia y al proyecto ATOS (POL2006-00550). Moira Llabrés ha recibido subvención a través del proyecto THRESHOLDS de la Comisión Europea.Peer reviewe

Picophytoplankton cell death induced by UV radiation: Evidence for oceanic Atlantic communities

We analyzed the effect of ambient levels of visible and ultraviolet radiation (UVR) on picophytoplankton cell death by exposing natural communities of picophytoplankton (Prochlorococcus, Synechococcus, and picoeukaryotic cells) from the Atlantic Ocean to different levels of natural solar radiation, from that received just below the surface to 23 % lower levels and dark conditions. Underwater oceanic levels of UVR and visible light can induce significant cell death in picophytoplankton communities. The decay rates of living cells induced by solar radiation was highest for Prochlorococcus sp., which showed an average decay rate of �0.24 � 0.053 h�1 (mean � SE) in the experiments, whereas Synechococcus sp. showed the lowest decay rate of �0.021 � 0.008 h�1 (mean � SE) in treatments ranging from the full incident irradiance to 23 % of the irradiance incident below the ocean surface. Decay rates decreased significantly upon removal of UVR, demonstrating a major effect of UVR on cell death, although ambient levels of visible light alone still induced cell death in Prochlorococcus and picoeukaryotic populations, but not in Synechococcus sp. The high cell death of Prochlorococcus induced by total solar radiation resulted in short halflife values for this genus, ranging between 1.5 and 13.4 h across treatments. The half-life times for Synechococcus sp. and eukaryotic picoplankton cells exposed to UVR were longer, varying from 8.8 to 14.7 h and from 2.1 to 31.7 h, respectively. The UVR doses required to reduce the picophytoplankton populations by 50 % (LRD50) differe

Diel in situ picophytoplankton cell death cycles coupled with cell division

The diel variability in picophytoplankton cell death was analyzed by quantifying the proportion of dead cyanobacteria Prochlorococcus and Synechococcus cells along several in situ diel cycles in the open Mediterranean Sea. During the diel cycle, total cell abundance varied on average 2.8±0.6 and 2.6±0.4 times for Synechococcus and Prochlorococcus populations, respectively. Increasing percentages of dead cells of Prochlorococcus and Synechococcus were observed during the course of the day reaching the highest values around dusk and decreasing as the night progressed, indicating a clear pattern of diel variation in the cell mortality of both cyanobacteria. Diel cycles of cell division were also monitored. The maximum percentage of dead cells (Max % DC) and the G2+M phase of the cell division occurred within a period of 2h for Synechoccoccus and 4.5h for Prochlorococcus, and the lowest fraction of dead cells occurred at early morning, when the maximum number of cells in G1 phase were also observed. The G1 maximum corresponded with the maximal increase in newly divided cells (minimum % dead cells), and the subsequent exposure of healthy daughter cells to environmental stresses during the day resulted in the progressive increase in dying cells, with the loss of these cells from the population when cell division takes place. The discovery of diel patterns in cell death observed revealed the intense dynamics of picocyanobacterial populations in nature. © 2011 Phycological Society of America.This is a contribution to the project BADE-1 (REN-2002-10606E/MAR) and MEDEICG (CTM2009-07013) funded by the Spanish Ministry of Science and Innovation to S. Agusti. M. Llabrés was supported by the project REN2001-5060-E/MAR, and ship time was provided by the Dutch Science Foundation (NWO-ALW project 812.03.001 to G. J. H).Peer Reviewe

Phytoplankton cell death induced by solar ultraviolet radiation

En esta tesis se ha demostrado que la radiación ultravioleta induce mortalidad en comunidades de fitoplancton de diferentes áreas del Océano Atlántico, del Mar Mediterráneo y del Océano Antártico. El fitoplancton más pequeño (pico-fitoplancton) muestra mayor sensibilidad a la radiación UV respecto al fitoplancton de mayor tamaño. Este estudio identifica que el crecimiento de las poblaciones del fitoplancton antártico está controlado por la radiación ultravioleta con inhibiciones de biomasas por encima del 80-90%. Se demuestra también que la transferencia de radicales OH, generados por la radiación ultravioleta, desde la atmósfera hacia la superficie del Océano causa mortalidad en comunidades de fitoplancton de aguas tropicales, templadas y antárticas. El trabajo presentado en esta tesis muestra la importancia de la radiación ultravioleta como factor que induce mortalidad en el fitoplancton, su influencia en el balance del crecimiento neto de estas poblaciones, así como las consecuencias que se derivan en la cadena trófica

Response of coastal Antarctic phytoplankton to solar radiation and ammonium manipulation: An in situ mesocosm experiment

We tested the role of solar irradiance and ammonium inputs on phytoplankton bloom formation in Antarctic coastal waters (62°39.576' S; 60°22.408' W, Livingston Island, South Sethlands) through the combination of a large-scale, in situ mesocosm experiment and a small-scale experiment. Phytoplankton growth, nutrient use, and biomass development remained low at ambient irradiances and increased greatly (greater than thirtyfold) to yield large (up to μg chlorophyll a 1-1) phytoplankton blooms in response to moderate shading. The phytoplankton communities tested were light limited when irradiance was reduced below 30% of the incident irradiance and stressed by high irradiance at the full ambient irradiance. Ammonium additions greatly stimulated phytoplankton growth, biomass, and stimulated the use of the large nitrate pool present in the Antarctic waters and lead to a decline in the specific UV absorption by mycosporinelike amminoacids. The small-scale experiment confirmed the role of UV irradiance in inhibiting phytoplankton growth and the capacity of ammonium inputs to overcome this inhibition. The alleviation of the high-irradiance stress by ammonium additions provided evidence of a key role of ammonium inputs in allowing phytoplankton to resume growth and nutrient use. The results demonstrate that there is a narrow window of irradiance where phytoplankton growth is adequate and that coastal Antarctic phytoplankton communities, examined here, are either light limited or stressed by high irradiance at. irradiances outside this range. More research is needed to analyze the interplay between light climate, ammonium, and bloom initiation in Antarctic coastal waters to test the generality of the results obtained. Copyright 2009 by the American Geophysical Union.Peer Reviewe

Synechococcus and Prochlorococcus cell death induced by UV radiation and the penetration of lethal UVR in the Mediterranean Sea

11 páginas, 6 figuras, 5 tablas. -- Artículo Open Access.Irradiation experiments performed on natural communities of picocyanobacteria from the southwest Mediterranean Sea indicated that natural levels of solar ultraviolet radiation (UVR: 280 to 400 nm) induced important cell death in Prochlorococcus sp., although Synechococcus sp. appeared to be highly resistant. In the treatments where UVB radiation (UVBR, 280 to 315 nm) was excluded, Prochlorococcus also experienced high cell death with short half-life times of 3.01 ± 0.1 SE (h), showing the contribution of UVA radiation (UVAR, 315 to 400 nm) and photosynthetically active radiation (PAR, 400 to 700 nm) to Prochlorococcus cell death. Underwater radiometric measurements conducted during the cruise indicated that penetration of UVR was significant in the Mediterranean waters studied, with minimum diffuse attenuation coefficients of 0.165 and 0.071 m–1 for 313 and 380 nm, respectively. The lethal UV doses required to decrease the picocyanobacteria populations by half, UVLRD50, calculated experimentally, were related to underwater UVR penetration in the Mediterranean Sea measured during the cruise. By calculating (from incident irradiances and UVR penetration) the daily UV doses at different depths in the water column, we found that, for sunny days, experimental Prochlorococcus LRD50 (187 kJ m–2) could reach from 10 to 26 m depth. For Synechococcus, however, the depth receiving daily UVLRD50 (1375 kJ m–2) was always shallower, above 5 m depth. The differential sensitivity of the 2 genera and the UV transparency of the Mediterranean Sea suggest that solar radiation could be an important factor influencing the dynamics and distribution of cyanobacterial populations in the surface waters of this oligotrophic sea.Este estudio fue financiado por la concesión REN-2002-10606E/MAR para Susana Agustí, financiada por el Ministerio de España de Educación y Cienca, y por la Netherlands Science Foundation,Earth and Life Sciences (NWO-ALW, proyecto n. #812.03.001 para Gerhard J. Herndl), por el proyecto EUROTROPH (Nutrients Cycling and the Trophic Status of Coastal Ecosystems) financiado por el Quinto Programa Marco de la Unión Europea y por el proyecto SESAME financiado por la Unión Europea también. Moira Llabrés fue financiada por el proyecto REN2001-5060E/MAR.Peer reviewe

Aerosol inputs enhance new production in the subtropical northeast Atlantic

8 pages, 3 figures, 1 table.Atmospheric deposition is an important source of limiting nutrients to the ocean, potentially stimulating oceanic biota. Atmospheric inputs can also deliver important amounts of organic matter, which may fuel heterotrophic activity in the ocean. The effect of atmospheric dry aerosol deposition on the metabolic balance and net production of planktonic communities remains unresolved. Here we report high inputs of aerosol-bound N, Si, P, Fe and organic C to the subtropical NE Atlantic and experimentally demonstrate these inputs to stimulate autotrophic abundance and metabolism far beyond the modest stimulation of heterotrophic processes, thereby enhancing new production. Aerosol dry deposition was threefold to tenfold higher in the coastal ocean than in the oyen ocean, and supplied high average (±SE) inputs of organic C (980 ± 220 μmol C m-2 d-1), total N (280 ± 70 μmol N m-2 d-1), Si (211 + 39 μmol Si m-2 d-1), and labile Fe (1.01 ± 0.19 μmol Fe m-2 d-1), but low amounts of total P (8 ± 1.6 μmol P m-2 d-1) to the region during the study. Experimental aerosol inputs to oceanic planktonic communities from the studied area resulted, at the highest doses applied, in a sharp increase in phytoplankton biomass (sevenfold) and production (tenfold) within 4 days, with the community shifting from a dominance of picocyanobacteria to one of diatoms. In contrast, bacterial abundance and production showed little response. Primary production showed a much greater increase in response to aerosol inputs than community respiration did, so that the P/R ratio increased from around 0.95 in the ambient waters, where communities were close to metabolic balance, to 3.3 at the highest nutrient inputs, indicative of a high excess production and a potential for substantial net CO2 removal by the community in response to aerosol inputs. These results showed that aerosol inputs are major vectors of nutrient and carbon inputs, which can, during high depositional events, enhance new production in the NE subtropical Atlantic Ocean.This research is part of the COCA (REN2000-1471-C02) and RODA (CTM-2004-06842-C03-O2) projects, funded by the Spanish "Plan Nacional de I+D". We thank NOAA Air Resources for access to the HYSPLIT model to generate the air mass back trajectories. We thank the crew of the R/V Hespérides and the technical UTM personnel involved for professional assistance. E A. and A. T. were supported by a fellowship from the Spanish Ministry of Education and Science, and C. M. D. and S. A. were supported by a sabbatical fellowship from the Spanish Ministry of Education and Science.Peer reviewe

Decline of autotrophic picoplankton in a warming subtropical ocean

Aquatic Sciences Meeting (Aquatic Sciences: Global And Regional Perspectives - North Meets South), 22-27 February 2015, Granada, Spain.The oligotrophic subtropical gyres represent with 70 percent of the ocean surface, the largest biome on Earth, where picoplankton represent the dominant autotrophs. Predicting the response of autotrophic picoplankton to warming in the subtropical ocean is, therefore, of major consequence for biogeochemical and ecological processes in the ocean. The trend for autotrophic picoplankton to increase with temperature in the ocean has lead to predictions that autotrophic picoplankton will increase with warming, in contrast with the documented trend towards a decline in autotroph biomass and production with warming and the associated stratification in the subtropical ocean. Here we show that warming and oligotrophication, with the associated increase in photosynthetic active radiation and UV-B radiation at depth, are expected to result in a decline by 18 to 42 percent in the abundance of autotrophic picoplankton, but an increase as the dominant component of the autotrophic community in the subtropical ocean. Our study is based in the large data set compiled during the Malaspina 2010 expedition, across the Atlantic, Indian and Pacific OceansPeer Reviewe