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Solar radiation has been measured in the high Andes near Laguna Lejia (latitude 23° 26' 23.30" S, longitude 67° 38' 14.29" W) at an elevation of 4715 m between December 2016 and December 2017. Irradiances were monitored in four wavelength channels: PAR (400-700 nm), UV-A (315-400 nm), UV-B (295-315 nm) and short-wavelength UV-B (295-310 nm) with a new radiometer. In addition, ambient temperatures were recorded. Record values have been found for PAR (exceeding 600 W m -2 ), UV-A (close to 95 W m -2 ), UV-B (3.13 W m -2 ) and short-wavelength UV-B (0.144 W m -2 ) during Austral spring. The winter irradiance values slightly exceeded 50% of these values. Maximal cloud effects due to multiple reflections were 45, 38, 32 and 35% higher than values under cloudless skies for PAR, UV-A, UV-B and short-wavelength UV-B, respectively. Record irradiance for this site shows a UV index reaching and exceeding 20, which is due to low solar zenith angles, the altitude, low water vapor and aerosol concentrations in the atmosphere as well as low total column ozone concentrations., (© 2020 American Society for Photobiology.)

We studied the temporal generation of reactive oxygen species (ROS) in the cyanobacterium Anabaena variabilis PCC 7937 under simulated solar radiation using WG 280, WG 295, WG 305, WG 320, WG 335, WG 345, and GG 400 nm cut-off filters to find out the minimum exposure time and most effective region of the solar spectrum inducing highest level of ROS. There was no significant generation of ROS in all treatments in comparison to the samples kept in the dark during the first 8 h of exposure; however, after 12 h of exposure, ROS were significantly generated in samples covered with 305, 295, or 280 nm cut-off filters. In contrast with ROS, the fragmentation of filaments was predominantly seen in 280 nm cut-off filter covered samples after 12 h of exposure. After 24 h of exposure, ROS levels were significantly higher in all samples than in the dark; however, the ROS signals were more pronounced in 320, 305, 295, or 280 nm cut-off filter covered samples. In contrast, the length of filaments was reduced in 305, 295, or 280 nm cut-off filter covered samples after 24 h of exposure. Thus, fragmentation of the filament was induced by all wavelengths of the UV-B region contrary to the UV-A region where only shorter wavelengths were able to induce the fragmentation. In contrast, ROS were generated by all wavelengths of the solar spectrum after 24 h of exposure; however, shorter wavelengths of both the UV-A and the UV-B regions were more effective in generating ROS in comparison to their higher wavelengths and photosynthetic active radiation (PAR). Moreover, lower wavelengths of UV-B were more efficient than the lower wavelengths of the UV-A radiation. Findings from this study suggest that certain threshold levels of ROS are required to induce the fragmentation of filaments.

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.

Continuing depletion of stratospheric ozone and subsequent increases in deleterious ultraviolet (UV) radiation at the Earth's surface have fueled the interest in its ecological consequences for aquatic ecosystems. The DNA is certainly one of the key targets for UV-induced damage in a variety of aquatic organisms. UV radiation induces two of the most abundant mutagenic and cytotoxic DNA lesions, cyclobutane pyrimidine dimers (CPDs) and pyrimidine pyrimidone photoproducts (6-4PPs) and their Dewar valence isomers. However, aquatic organisms have developed a number of repair and tolerance mechanisms to counteract the damaging effects of UV on DNA. Photoreactivation with the help of the enzyme photolyase is one of the most important and frequently occurring repair mechanisms in a variety of organisms. Excision repair, which can be distinguished into base excision repair (BER) and nucleotide excision repair (NER), also play an important role in DNA repair in several organisms with the help of a number of glycosylases and polymerases, respectively. In addition, mechanisms such as mutagenic repair or dimer bypass, recombinational repair, cell-cycle checkpoints, apoptosis and certain alternative repair pathways are also operative in various organisms. This review deals with the UV-induced DNA damage and repair in a number of aquatic organisms as well as methods of detecting DNA damage.

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.

Aquatic ecosystems are a key component of the Earth's biosphere. A large number of studies document substantial impact of solar UV radiation on individual species, yet considerable uncertainty remains with respect to assessing impacts on ecosystems. Several studies indicate that the impact of increased UV radiation appears relatively low when considering overall ecosystem response, while, in contrast, effects on individual species show considerable responses. Ecosystem response to climate variability incorporates both synergistic and antagonistic processes with respect to UV-related effects, significantly complicating understanding and prediction at the ecosystem level. The impact of climate variability on UV-related effects often becomes manifest via indirect effects such as reduction in sea ice, changes in water column bio-optical characteristics, changes in cloud cover and shifts in oceanographic biogeochemical provinces.

The effect of UV and visible light on cyanobacteria was determined at the cellular level by means of epifluorescence and confocal microscopy techniques. These methods allow the examination of light effects in spatial resolution. Series of measurements were performed to determine the effect of different light qualities and quantities on cyanobacteria. To analyze the effect of the light quality, samples of Anabaena and Scytonema sp. were exposed to intense blue, green or red light applied from the epifluorescence path of the microscope. The fluorescence of the phycobiliproteins was recorded by means of epifluorescence (excitation 550 nm, 20 nm half band width (HBW), emission above 635 nm) or by confocal microscopy (560 nm laser line). Upon exposure to blue or green light the cells showed an increase in fluorescence followed by a sudden and complete loss of fluorescence. Blue light was more effective (bleaching of phycobiliproteins within 45 min) than green light (bleaching within 120 min). Red light was not as effective, and bleaching of the cells took at least 24 h. Initially the cells showed an increase in fluorescence followed by fast bleaching of the fluorescence signal. Cells exposed to UV plus PAR were bleached within 60 min, while cells exposed to photosynthetically active radiation (PAR) only were totally bleached after about 120 min. FL-DHP (dihydropyridine) labeling was performed in two cyanobacteria, Anabaena sp. and Nostoc commune, to visualize L-type calcium channels. Both cyanobacterial strains showed a pronounced FL-DHP signal of the heterocysts and akinetes but only a weak signal from the vegetative cells. The results clearly indicate the presence of calcium channels in these cells. UV radiation decreased the amount of chlorophyll and phycocyanin as could be seen from a decline in the autofluorescence of the cells. In contrast, the FL-DHP signal was not affected by UV.

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, Möhrendorf, 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 (ELDONET) project has been designed with the purpose of establishing an efficient system to monitor solar radiation in Europe, in as many as possible locations. This paper describes the structure of the server that collects and processes the data acquired by the different stations belonging to the network, and makes them freely available on the Internet to the scientific community. The server is able to receive data either via FTP from the Internet or via modem and to process them looking for errors or inconsistencies. Moreover, it automatically generates graphs, Web-pages and FTP archives. The server has been active for some years in testing mode and is now fully operative.

The effects of solar radiation (PAR, UVA, UVB) on the productivity and structure of diatom and invertebrate assemblages were assessed during primary succession on artificial substrate near a rocky shore of the Saronikos Gulf, Greece. Three light treatments were performed (PAR, PAR+UVA, and PAR+UVA+UVB) at 0.5, 1.0 and 1.5 m of depth. Pennate diatoms were the major component of the developing periphytic communities during the study period. Exposure to solar UVB initially reduced the biomass and altered the structure of the diatom assemblages. The highest biomass of diatom assemblages was observed under PAR (49.2 g/m2). This value was significantly higher than the biomass of assemblages growing under PAR+UVA+UVB, but not significantly different compared to the biomass of assemblages exposed to PAR+UVA. These differences, however, did not persist at later stages. The most abundant invertebrate groups present were Polychaetes and Crustaceans. Solar UVB did not have significant effects on invertebrate biomass. Analysis of the invertebrate assemblage structure revealed time-course differences but no clear trends among the different treatments.

Cultures of the marine dinoflagellate Gyrodinium dorsum have been exposed to polychromatic radiation (photosynthetically active radiation and UV) from a solar simulator for up to 72 h. Different irradiance spectra in the ultraviolet are produced by inserting cut-off filters between lamp and samples. The mycosporine-like amino acid (MAA) content and composition are investigated by spectroscopic and chromatographic analysis. The study reveals that G. dorsum contains a complex mixture of several aminocyclohexenimine-MAAs and one aminocyclohexenone-MAA. UV irradiation around 320 nm induces an increase in the concentration of all MAAs in the samples. In contrast, exposure to short-wavelength UV-B radiation results in decreased overall MAA production. Furthermore, there is a spectral shift in the absorption of the MAA mixture towards shorter wavelengths, indicating that short-wavelength UV-B induces an altered MAA composition. The amount of MAAs is normalized to the chlorophyll a concentration.