Vertical migration and motility responses in three marine phytoplankton species exposed to solar radiation

Diurnal vertical migration in the water column and the impact of solar radiation on motility were investigated in three marine phytoplankton species: Tetraselmis suecica, Dunaliella salina and Gymnodinium chlorophorum. Cells were exposed to solar radiation either in ultraviolet radiation (UVR, 280-400 nm) transparent Plexiglas tubes (45 cm length, 10 cm diameter) or in quartz tubes under three radiation treatments: PAB (280-700 nm), PA (320-700 nm) and P (400-700 nm). The three species displayed different behavior after exposure to solar radiation. Tetraselmis suecica was insensitive to UVR and under high solar radiation levels, cells accumulated preferentially near the surface. Exposure experiments did not indicate any significant changes in swimming speed nor in the percentage of motile cells after 5 h of exposure. On the other hand, D. salina was sensitive to UV-B displaying a significant decrease in swimming speed and percentage of motile cells after 2-3 h of exposure. Moreover, D. salina cells migrated deep in the water column when irradiance was high. The response of G. chlorophorum was in between that of the other two species tested, with a slight (but significant) decrease in swimming speed and percentage of motile cells in all radiation treatments after 5 h of exposure. While G. chlorophorum cells were more or less homogenously distributed in the water column, a slight (but significant) avoidance response to high radiation was observed at local noon, with cells migrating deep in the water column. Our data clearly indicate that these sub-lethal effects of solar radiation are species-specific and they might have important implications for the aquatic ecosystem.     

Effects of solar ultraviolet radiation on photosynthesis of the marine red tide alga Heterosigma akashiwo (Raphidophyceae)

In order to assess the short- and long-term impacts of UV radiation (UVR, 280-400nm) on the red tide alga, Heterosigma akashiwo, we exposed the cells to three different solar radiation treatments (PAB: 280-700nm, PA: 320-700nm, P: 400-700nm) under both solar and artificial radiation. A significant decrease in the effective quantum yield (Y) during high irradiance periods (i.e., local noon) was observed, but the cells partially recovered during the evening hours. Exposure to high irradiances for 15, 30, and 60min under a solar simulator followed by the recovery (8h) under dark, 9 and 100micromolphotonsm(-2)s(-1) of PAR, highlighted the importance of the irradiance level during the recovery period. Regardless the radiation treatments, the highest recovery (both in rate and total Y) was found at a PAR irradiance of 9micromolphotonsm(-2)s(-1), while the lowest was observed at 100micromolphotonsm(-2)s(-1). In all experiments, PAR was responsible for most of the observed inhibition; nevertheless, the cells exposed only to PAR had the highest recovery in any condition, as compared to the other radiation treatments. In long-term experiments (10 days) using semi-continuous cultures, there was a significant increase of UV-absorbing compounds (UV(abc)) per cell from 1.2 to >4x10(-6)microgUV(abc)cell(-1) during the first 3-5 days of exposure to solar radiation. The highest concentration of UV(abc) was found in samples exposed in the PAB as compared to PA and P treatments. Growth rates (mu) mimic the behavior of UV-absorbing compounds, and during the first 5 days mu increased from <0.2 to ca. 0.8, and stayed relatively constant at this value during the rest of the experiment. The inhibition of the Y decreased with increasing acclimation of cells. All our data indicates that H. akashiwo is a sensitive species, but was able acclimate relatively fast (3-5 days) synthesizing UV-absorbing compounds and thus reducing any impact either on photosystem II or on growth.     

Impact of solar ultraviolet radiation on marine phytoplankton of Patagonia, Argentina

Patagonia area is located in close proximity to the Antarctic ozone "hole" and thus receives enhanced ultraviolet B (UV-B) radiation (280-315 nm) in addition to the normal levels of ultraviolet A (UV-A; 315-400 nm) and photosynthetically available radiation (PAR; 400-700 nm). In marine ecosystems of Patagonia, normal ultraviolet radiation (UVR) levels affect phytoplankton assemblages during the three phases of the annual succession: (1) prebloom season (late summer-fall), (2) bloom season (winter-early spring) and (3) postbloom season (late spring-summer). Small-size cells characterize the pre- and postbloom communities, which have a relatively high photosynthetic inhibition because of high UVR levels during those seasons. During the bloom, characterized by microplankton diatoms, photosynthetic inhibition is low because of the low UVR levels reaching the earth's surface during winter; this community, however, is more sensitive to UV-B when inhibition is normalized by irradiance (i.e. biological weighting functions). In situ studies have shown that UVR significantly affects not only photosynthesis but also the DNA molecule, but these negative effects are rapidly reduced in the water column because of the differential attenuation of solar radiation. UVR also affects photosynthesis versus irradiance (P vs E) parameters of some natural phytoplankton assemblages (i.e. during the pre- but not during the postbloom season). However, there is a significant temporal variability of P vs E parameters, which are influenced by the nutrient status of cells and taxonomic composition; taxonomic composition is in turn associated with the stratification conditions (e.g. wind speed and duration). In Patagonia, wind speed is one of the most important variables that conditions the development of the winter bloom by regulating the depth of the upper mixed layer (UML) and hence the mean irradiance received by cells. Studies on the interactive effects of UVR and mixing show that responses of phytoplankton vary according to the taxonomic composition and cell structure of assemblages; therefore cells use UVR if >90% of the euphotic zone is being mixed. In fact, cell size plays a very important role when estimating the impact of UVR on phytoplankton, with large cells being more sensitive when determining photosynthesis inhibition, whereas small cells are more sensitive to DNA damage. Finally, in long-term experiments, it was determined that UVR can shape the diatom community structure in some assemblages of coastal waters, but it is virtually unknown how these changes affect the trophodynamics of marine systems. Future studies should consider the combined effects of UVR on both phytoplankton and grazers to establish potential changes in biodiversity of the area.     

Variable fluorescence parameters in the filamentous Patagonian rhodophytes, Callithamnion gaudichaudii and Ceramium sp. under solar radiation

The filamentous rhodophytes Callithamnion gaudichaudi Agardh and Ceramium sp. were utilized to study the effects of solar radiation (PAR, 400-700 nm, UV-B, 280-315 nm and UV-A, 315-400 nm) on the photosynthetic performance in situ in Patagonia waters (Argentina). A pulse amplitude modulated (PAM) fluorometer was used to determine the fluorescence parameters. The two species grew in different habitats in the eulittoral: Ceramium sp. was found only in rock pools while C. gaudichaudii grew on exposed rocks and fell dry during low tide. Both species differed in their fluorescence parameters and their sensitivity to solar radiation exposure. The photosynthetic quantum yield had its lowest values at noon, but it recovered in the afternoon/evening hours, when irradiances were lower. PAR (irradiance of about 400 W m(-2) at noon) was responsible for most of the decrease in the yield on clear days, especially in Ceramium sp., but UVR (280-400 nm) also accounted for a significant decrease. Fluence rate response curves indicated that both species were adapted to low fluence rates and showed a pronounced non-photochemical quenching at intermediate and higher irradiances. Both species showed a rapid adaptation during measurement of fast induction kinetics but differed significantly in their fluorescence components. All photosynthetic pigments were bleached after 8 h exposure to solar radiation over a full day. Strong absorption in the UV-A range, most likely due to mycosporine-like amino acids, was detected in both strains. The pronounced sensitivity to solar radiation in situ and the recovery capacity of these two filamentous Rhodophyte species, as well as the presence of protective compounds, suggests that these algae have the ability to adapt to the relatively high radiation levels and changes in irradiance found in the Patagonia waters.     

Dynamics of potentially protective compounds in Rhodophyta species from Patagonia (Argentina) exposed to solar radiation

The impact of solar radiation upon potentially protective compounds (i.e., UV-absorbing compounds and carotenoids) was assessed in four Rhodophyte species from Patagonia (i.e., Ceramium sp. Lyngbye, Corallina officinalis Linnaeus, Callithamnion gaudichaudii Agardh and Porphyra columbina Montagne) during short-term (i.e., 46 h) experiments. Algae were exposed to solar radiation under two treatments (PAR only: 400-700 nm, and PAR+UVR: 280-700 nm) and sub-samples were taken every 3 h (or longer periods at night) to determine the spectral absorption characteristics and concentration of UV-absorbing compounds, carotenoids and photosynthetic pigments. Except for C. gaudichaudii which displayed a decrease in chl-a concentration throughout the experiment, photosynthetic pigments had small variations in all species. UV-absorbing compounds concentration had species-specific responses: Ceramium sp. was the only species in which UV-absorbing compounds concentration varied as a function of solar irradiance, with maximum values around local noon. In C. officinalis and P. columbina UV-absorbing compounds concentration increased as compared to that of chl-a; in Ceramium sp. and C. gaudichaudii, however, there was no relationship between UV-absorbing compounds content and chl-a concentration. Carotenoids, on the other hand, did co-vary with chl-a in all species. Our data suggest that, with the exception of C. gaudichaudii, the differential responses of UV-absorbing compounds concentrations are more associated to the previous light history of the algae (i.e., in turn due to their position in the intertidal zone) rather than to the radiation treatment imposed to the samples. Based on our results, the variable impact of solar radiation upon productivity (and eventually biodiversity) of macroalgae from Patagonia might consequently differentially affect higher trophic levels of the aquatic food web.     

Variability of UVR effects on photosynthesis of summer phytoplankton assemblages from a tropical coastal area of the South China Sea

From June to September 2005, we carried out experiments to determine the ultraviolet radiation (UVR) -induced photoinhibition of summer phytoplankton assemblages from a coastal site of the South China Sea. Variability in taxonomic composition was determined throughout the summer, with a peak chlorophyll a (chl a approximately 20 microg chl a L(-1)) dominated by the diatom Skeletonema costatum that was detected early in the study period; the rest of the time samples were characterized by monads and flagellates, with low chl a values (1-5 chl a microg L(-1)). Surface water samples were placed in quartz tubes, inoculated with radiocarbon and exposed to solar radiation for 2-3 h to determine photosynthetic rates under three quality radiation treatments (i.e. PAB, 280-700 nm; PA, 320-700 nm and P, 400-700 nm) using different filters and under seven levels of ambient irradiance using neutral density screens (P vs E curves). UVR inhibition of samples exposed to maximum irradiance (i.e. at the surface) varied from -12.2% to 50%, while the daytime-integrated UVR-related photoinhibition in surface seawater varied from -62% to 7%. The effects of UVR on the photosynthetic parameters P(B)(max) and E(k) were also variable, but UV-B accounted for most of the observed variability. During sunny days, photosynthesis of microplankton (>20 microm) and piconanoplankton (<20 microm) were significantly inhibited by UVR (mostly by UV-B). However, during cloudy days, while piconanoplankton cells were still inhibited by UVR, microplankton cells used UVR (mostly UV-A) as the source of energy for photosynthesis, resulting in higher carbon fixation in samples exposed to UVR than the ones exposed only to photosynthetically active radiation (PAR). Our results indicate that size structure and cloudiness clearly condition the overall impact of UVR on phytoplankton photosynthesis in this tropical site of South China. In addition, model predictions for this area considering only PAR for primary production might have underestimated carbon fixation due to UVR contribution.     

Combined effects of solar ultraviolet radiation and nutrients addition on growth, biomass and taxonomic composition of coastal marine phytoplankton communities of Patagonia

Experiments (6-8 days) were conducted during late summer, late fall and late winter, 2003 with waters collected off Bahía Nueva, Chubut, Argentina (42.7 degrees S, 65 degrees W) to determine the combined effects of solar ultraviolet radiation (UVR, 280-400 nm) and nutrient addition on phytoplankton communities. Samples were put in UVR-transparent containers and incubated under two radiation treatments: (a) Samples exposed to full solar radiation (PAB treatment, 280-400 nm) and (b) Samples exposed only to PAR (PAR treatment, 400-700 nm). At the beginning of the experiments, nutrients (i.e., NaPO(4)H(2) and NaNO(3)) were added to one set of samples from each radiation treatment (N cultures) whereas in the other set, nutrients remained at the concentration of the seawater. Chlorophyll a, biomass, UV-absorbing compounds and taxonomic composition were recorded throughout the experiments. N cultures always had significantly higher growth rates (P<0.05) than that in non-enriched cultures. At the beginning of experiments, phytoplankton communities were generally dominated by monads and flagellates but by the end, diatoms comprised the bulk of biomass, with only one to four taxa dominating, suggesting a selection towards more tolerant/less sensitive species. Over the experimental time frame, the observed taxonomic changes were mostly due to nutrient availability, and to a lesser extent to solar UVR exposure. Overall, the results indicate that environmental conditions (i.e., light history, nutrient concentration) together with the physiological status of the cells play a very important role at the time to assess the combined effect of nutrient addition and solar radiation on coastal phytoplankton assemblages from Patagonia.     

Interactive effects of ultraviolet radiation and nutrient addition on growth and photosynthesis performance of four species of marine phytoplankton

Experiments (6-8 days) were carried out during the austral summer of 2005 in Chubut, Argentina (43 degrees S, 65 degrees W) to determine the interactive effects of solar UVR (280-400 nm) and nutrient addition on growth and chlorophyll fluorescence of four species of marine phytoplankton--the diatoms Thalassiosira fluviatilis Hustedt and Chaetoceros gracilis Schütt, and the dinoflagellates Heterocapsa triquetra (Ehrenberg) Stein and Prorocentrum micans (Ehrenberg). Samples were incubated under three radiation treatments (two sets of each radiation treatment): (a) samples exposed to full solar radiation (PAR+UVR, PAB treatment, 280-700 nm); (b) samples exposed to PAR and UV-A (PA treatment, 320-700 nm) and (c) samples exposed only to PAR (P treatment, 400-700 nm). At the beginning of the experiments, nutrients (i.e., NaPO(4)H(2) and NaNO(3)) were added to one set of samples from each radiation treatment ("N" cultures) whereas in the other, the nutrients concentration was that of the culture medium. At all times, the lowest growth rates (mu) were determined in the PAB treatments, where enriched cultures had significantly higher mu (P<0.05) than non-enriched cultures. Daily cycles of photochemical quantum yield (Y) displayed a pattern of relatively high values early in the morning with a sharp decrease at noon; recovery was observed late in the afternoon. In general, higher Y values were determined in enriched cultures than in non-enriched cultures. As the experiments progressed, acclimation (estimated as the difference between Y at noon and that at time zero) was observed in all species although in variable degree. All species displayed some degree of UVR-induced decrease in the photochemical quantum yield, although it was variable among treatments and species. However, this effect decreased with time, and this pattern was more evident in the dinoflagellates, as the concentration of UV-absorbing compounds increased. Thus, under conditions of nutrient enrichment as may occur by river input or by re-suspension by mixing, dinoflagellates outcompete with diatoms because they may have a higher fitness under UVR stress.     

EFFECTS OF SOLAR AND ARTIFICIAL UV IRRADIATION ON MOTILITY AND PHOTOTAXIS IN THE FLAGELLATE, Euglena gracilis

The effect of solar irradiation on the percentage of motile cells, their average speed and their phototactic orientation to white actinic light was studied in the flagellate, Euglena gracilis. Unfiltered solar radiation in midsummer during mid-day at a location near Lisboa, Portugal, was found to impair motility within 2 h. This effect is exclusively due to the UV-B component of the radiation and not due to UV-A, visible light or a temperature increase. Likewise, phototactic orientation was drastically impaired. Reduction of the solar UV-B irradiation by insertion of an ozone-Hooded plexiglass cuvette partially reduced the inhibition and covering the cuvettes with glass prevented any decrease in motility and photoorientation. Similar results were found with artificial irradiation (Xe lamps). After inoculation the motility of the population follows an optimum curve (optimum at 8 days). Also, the UV-B effect on motility was smallest after about one week and increased for younger and older cultures.     

IMPACT OF UV-B RADIATION UPON ESTUARINE MICROCOSMS

Abstract— Twelve flow-through estuarine microcosms were exposed daily to four different levels of UV-B radiation (290–320. nm)(1.57 ± 10², 6.43 ± 10³, 6.86 ± 10³ and 7.61 ± 10³ J·m_-2d⁻¹) in addition to a natural level of visible solar radiation (380-800. nm). The parameters studied over a four week period were phytoplankton community composition, plankton biomass (ash-free dry weight), chlorophyll a concentration and primary productivity (radiocarbon uptake). With increased exposure to UV-B radiation there was an obvious alteration of the community composition. Daily exposure to enhanced levels of UV-B radiation also depressed the biomass, the chlorophyll a concentration and the radiocarbon uptake of samples from the ecosystems.     

Biological Impact of Shorter Wavelength Ultraviolet Radiation-C†

Life on earth has constantly coped with the impact of solar radiation, especially solar ultraviolet radiation (solar UV). Various biological mechanisms protect us from solar UV. New devices emitting shorter wavelengths UV-C, i.e. <254 nm emitted by conventional UV germicidal lamps, have emerged. These shorter wavelength UV-C emitting devices are useful for various purposes, including microorganism inactivation. However, as solar UV-C does not reach the earth surface, biological impacts of UV-C has been studied using 254 nm germicidal lamps, and those using shorter wavelength UV-C is rarely known. To balance the utility and risk of UV-C, the biological effect of these new UV-C emitting devices must be investigated. In addition, our knowledge of biological impacts of the wavelength-dependent entire UV (100–400 nm) must be enhanced. In this review, we briefly summarize the biological impacts of shorter wavelength UV-C. Mechanisms of UV-C-induced cellular damage and factors affecting the microorganism inactivation efficiency of UV-C have been discussed. In addition, we theoretically estimate the probable photocarcinogenic action spectrum of shorter wavelength UV-C. We propose that increasing the knowledge on UV-C will facilitate the adoption of shorter wavelength UV-C emitting new devices in an optimal and appropriate manner.     

Effects of solar radiation on the Patagonian macroalga Enteromorpha linza (L.) J. Agardh-Chlorophyceae.

The photosynthetic performance of Enteromorpha linza (L.) J. Agardh-Chlorophyceae was determined with a portable PAM instrument in situ and under seminatural radiation conditions in Patagonia, Argentina. Solar radiation was measured in parallel with a three-channel radiometer, ELDONET (Real Time Computer, M?hrendorf, Germany), in three wavelength ranges, UV-B (280-315 nm), UV-A (315-400 nm), and PAR (400-700 nm). The effective photosynthetic quantum yield decreased after 15-min exposure to solar radiation when the thalli were kept in a fixed position but recovered in the subsequent shade conditions within several hours. A 30-min exposure of free floating thalli, however, caused less photoinhibition. The photosynthetic quantum yield of E. linza was also followed over whole days under clear sky, partly cloudy and rainy conditions in a large reservoir of water (free floating thalli) and in situ (thalli growing in rock pools). Most of the observed effect was due to visible radiation; however, the UV wavelength range, and especially UV-B, caused a significant reduction of the photosynthetic quantum yield. Fluence rate response curves indicated that the species is a typical shade plant which showed non-photochemical quenching at intermediate and higher irradiances. This is a surprising result since these algae are found in the upper eulittoral where they are exposed to high irradiances. Obviously they utilize light only during periods of low irradiances (morning, evening, high tide) while they shut down the electron transport chain during intensive exposure. Fast induction and relaxation kinetics have been measured in these algae for the first time and indicated a rapid adaptation of the photosynthetic capacity to the changing light conditions as well as a fast decrease of PS II fluorescence upon exposure to solar radiation. There was a strong bleaching of chlorophyll due to exposure to solar radiation but less drastic bleaching of carotenoids.     

The European Light Dosimeter Network: four years of measurements

The European Light Dosimeter Network (ELDONET) has now been functional for more than four years. The network is based on dosimeters which measure radiation in three biologically relevant wavelength bands (UV-B, 280-315 nm; UV-A, 315-400 nm; and Photosynthetic Active Radiation, PAR, 400-700 nm). The ELDONET network is currently based on 33 stations with 40 instruments. The distribution of the instruments all over Europe allows measurement of the latitudinal and longitudinal light climate distribution. In addition, several instruments are active in South America, New Zealand, India, Africa and Japan. With some exceptions, the measured yearly doses depend on the latitude. While the maximal daily doses are almost comparable from station to station, seasonal changes and the different maximal solar zenith angles account for the differences in total yearly doses. Ratioing between UV-B and PAR allows the detection of subtle changes in the local light climate, due, for example, to mini-ozone holes encountered in northern Europe during spring. Comparison of satellite ozone data with terrestrial ELDONET measurements revealed an overall weak correlation between these data sets. However, local weather conditions, solar zenith angle and latitude as well as reflectivity (i.e. clouds and aerosol; satellite data) show a much stronger correlation to the doses received. The close relationship between the spectral sensitivity of the UV-B sensor used in the ELDONET dosimeter and the CIE erythemal action spectrum allows determination of the erythemal dose on the basis of the dosimeter readings.     

Influence of temperature and UVR on photosynthesis and morphology of four species of cyanobacteria

During the late austral spring of 2009 we carried out experiments (4days of duration) with four cyanobacteria species, Anabaena sp., Nostoc sp., Arthrospira platensis and Microcystis sp., to assess the combined effects of temperature and solar radiation on photosynthesis performance and morphology. Two experimental temperatures (18°C and 23°C, simulating a 5°C increase under a scenario of climate change) and three radiation treatments (by using different filters/materials) were implemented: (i) P (PAR, 400-700nm), (ii) PA (PAR+UV-A, 320-700nm) and, (iii) PAB (PAR+UV-A+UV-B, 280-700nm). In general, samples under the P treatment had less decrease/higher recovery rates of effective photochemical quantum yield (Y) than those receiving UV-A or UV-A+UV-B. The effects of increased temperature were species-specific: At the end of the experiments, it was seen that increased temperature benefited photosynthetic performance of Anabaena sp. and Nostoc sp. but not of Microcystis sp. and A. platensis. Higher temperature was also associated to an increase in the chain area of Anabaena sp., and to bigger trichomes in A. platensis; however, no morphological effects were observed in Microcystis sp. In addition, in Nostoc sp. the increase in temperature counteracted the UVR impact on the reduction of the chain area. How these effects and mechanisms will affect the trophodynamics and production of aquatic ecosystems is still uncertain, but the specificity of the responses suggests that not all cyanobacteria would be equally benefited by temperature increases therefore affecting the balance and interaction among species in the water column.     

The role of solar UV radiation in the ecology of alpine lakes.

Solar ultraviolet radiation (UVR, 290-400 nm) is a crucial environmental factor in alpine lakes because of the natural increase of the UVR flux with elevation and the high water transparency of these ecosystems. The ecological importance of UVR, however, has only recently been recognized. This review, examines the general features of alpine lakes regarding UVR, summarizes what is known about the role of solar UVR in the ecology of alpine lakes, and identifies future research directions. Unlike the pattern observed in most lowland lakes, variability of UV attenuation in alpine lakes is poorly explained by differences in dissolved organic carbon (DOC) concentrations, and depends mainly on optical characteristics (absorption) of the chromophoric dissolved organic matter (CDOM). Within the water column of lakes with low DOC concentrations (0.2-0.4 mg l(-1)), UV attenuation is influenced by phytoplankton whose development at depth (i.e. the deep chlorophyll maximum) causes important changes in UV attenuation. Alpine aquatic organisms have developed a number of strategies to minimize UV damage. The widespread synthesis or bioaccumulation of different compounds that directly or indirectly absorb UV energy is one such strategy. Although most benthic and planktonic primary producers and crustacean zooplankton are well adapted to high intensities of solar radiation, heterotrophic protists, bacteria, and viruses seem to be particularly sensitive to UVR. Understanding the overall impact of UVR on alpine lakes would need to consider synergistic and antagonistic processes resulting from the pronounced climatic warming, which have the potential to modify the UV underwater climate and consequently the stress on aquatic organisms.     

Photosynthetically active sunlight at high southern latitudes

A network of scanning spectroradiometers has acquired a multiyear database of visible solar irradiance, covering wavelengths from 400 to 600 nm, at four sites in the high-latitude Southern Hemisphere, from 55 degrees S to 90 degrees S. Monthly irradiations computed from the hourly measurements reveal the character of the seasonal cycle and illustrate the role of cloudiness as functions of latitude. Near summer solstice, the combined influences of solar elevation and the duration of daylight would produce a monthly irradiation with little latitude dependence under clear skies. However, the attenuation associated with local cloudiness varies geographically, with the greatest effect at the most northern locations, Ushuaia, Argentina and Palmer Station on the Antarctic Peninsula. Near summer solstice, the South Pole experiences the largest monthly irradiation of the sites studied, where relatively clear skies contribute to this result. Scaling factors derived from radiative-transfer calculations combined with the measured 400-600 nm irradiances allow estimating irradiances integrated over the wavelength band 400-700 nm. This produces a climatology of photosynthetically active radiation for each month of the year at each site.     

Solar PAR and UV radiation affects the physiology and morphology of the cyanobacterium Anabaena sp. PCC 7120

Solar UV radiation (280-400 nm) may affect morphology of cyanobacteria, however, little has been evidenced on this aspect while their physiological responses were examined. We investigated the impacts of solar PAR and UVR on the growth, photosynthetic performance and morphology of the cyanobacterium Anabaena sp. PCC7120 while it was grown under three different solar radiation treatments: exposures to (a) constant low PAR (photosynthetic active radiation, 400-700 nm), (b) natural levels of solar radiation with and (c) without UV radiation (290-400 nm). When the cells were exposed to solar PAR or PAR+UVR, the photochemical efficiency was reduced by about 40% and 90%, respectively, on day one and recovered faster under the treatment without UVR over the following days. Solar UVR inhibited the growth up to 40%, reduced trichome length by up to 49% and depressed the differentiation of heterocysts. Negligible concentrations of UV-absorbing compounds were found even in the presence of UVR. During the first 2 d of exposure to natural levels of PAR, carotenoid concentrations increased but no prolonged increase was evident. Heterocyst formation was enhanced under elevated PAR levels that stimulated quantum yield and growth after an initial inhibition. Higher concentrations of carotenoids and a twofold increase in the carotenoid to chlorophyll a ratio provided protection from the high levels of solar PAR. Under radiation treatments with UVR the relatively greater decrease in chlorophyll a concentrations compared with the increase in carotenoids was responsible for the higher carotenoid: chlorophyll a ratio. Heterocyst formation was disrupted in the presence of solar UVR. However, the longer term impact of heterocyst disruption to the survival of Anabaena sp. requires further study.     

UV Exposition During Typical Lifestyle Behavior in an Urban Environment

In this study the personal exposure to solar UV radiation in an urban environment was measured. Lifestyle in an urban environment is characterized by staying indoors during most of the day. Furthermore, the ambient UV radiation is mitigated by shadowing by buildings. The aim of the study was to find out activities which may contribute to UV-induced health risk in a low exposure environment. Exposure was measured during typical outdoor activities: shopping, walking, sitting in a sidewalk café, cycling, sightseeing and at an open-air pool (solar elevation: 10°–70°). Measurements were taken with an optoelectronic device which was fixed on the chest. Besides the UV Index we used the sun burn time (SBT) for risk assessments. Generalization of our results was made by calculating ratios of personal exposure to the ambient UV radiation. UV exposure was by far the highest when our study subject stayed at the swimming pool. The SBT was around 30 min for melano-compromised skin type. For all other activities, except shopping, the SBT range up to 1 h. With respect to photodamage we found that at high solar elevation (>45°) photoprotective measures should be applied for certain activities even within a city.     

Differential impacts of solar UV radiation on photosynthetic carbon fixation from the coastal to offshore surface waters in the South China Sea

We carried out experiments during an expedition (14 August to 14 September, 2007) that covered up to 250,000 km(2) to investigate the effects of solar UV radiation (UVR, 280-400 nm) on the photosynthetic carbon fixation of tropical phytoplankton assemblages in surface seawater of the South China Sea. From coastal to pelagic surface seawaters, UV-B (280-315 nm) caused similar inhibition, while UV-A (315-400 nm) induced photosynthetic inhibition increased from coastal to offshore waters. UV-B resulted in an inhibition by up to 27% and UV-A by up to 29%. Under reduced levels of solar radiation with heavy overcast, UV-A resulted in enhanced photosynthetic carbon fixation by up to 25% in coastal waters where microplankton was abundant. However, such a positive impact was not observed in the offshore waters where piconanoplankton was more abundant. The daily integrated inhibition of UV-A reached 4.3% and 13.2%, and that of UV-B reached 16.5% and 13.5%, in the coastal and offshore waters, respectively.     

Photomovement of the swarmers of the brown algae Scytosiphon lomentaria and Petalonia fascia: effect of photon irradiance, spectral composition and UV dose

Photomovement measurements were carried out with swarmers of the brown algae Scytosiphon lomentaria (Lyngb.) Link and Petalonia fascia (O. F. Müll.) as a function of irradiance direction, photon irradiance, spectral composition and ultraviolet radiation (UVR, lambda=280-400 nm) dose. Swarmers from both species showed similar photomovement patterns: negative phototaxis occurred under photon irradiances of 10-90 micromol photons m(-2) s(-1), and no movement was observed at 190 micromol photons m(-2) s(-1). The translocational velocity measured between 10 and 90 micromol m(-2) s(-1) ranged from 100 to 200 microm s(-1). The accumulation of swarmers presented a peak at 450 nm (waveband of 50 nm), and smaller peaks at 400 and 500 nm; no effect was observed at wavelengths of 550 nm and above. The decline in phototactic index (an estimator of photomovement response) of swarmers was linearly correlated with the logarithm of UVR doses. These data were correlated with levels of natural solar radiation in the field. It is hypothesized that motility of swarmers could be a critical factor in the survival of these species under a scenario of increased UVR.