Seasonal Impacts of Solar UV Radiation on Photosynthesis of Phytoplankton Assemblages in the Coastal Waters of the South China Sea

Nitrogen-limitation exacerbates the impact of ultraviolet radiation on the coccolithophore Gephyrocapsa oceanica

To investigate effects of UV radiation (UVR, 280-400 nm) on coccolithophorids under nutrient-limited conditions, we grew Gephyrocapsa oceanica to determine its resilience to consecutive daily short-term exposures to +UVR (irradiances >295 nm) under a range of nitrate availabilities (100, 24, 12, 6 and 3 μM). +UVR alone significantly hampered the growth of G. oceanica, with the synergistic negative effects of +UVR and N-limitation being about 58% and 22% greater than under UVR or N-limitation alone, respectively. Most 3 μM nitrate cultures died, but those exposed to UVR succumbed sooner. This was due to a failure of photoprotection and repair mechanisms under low N-availability with exposures to UVR. Additionally, the UVR-induced inhibition of the effective quantum yield of photosystem II (PSII) was significantly higher and was further aggravated by N limitation. The algal cells increased photoprotective pigments and UV-absorbing compounds as a priority rather than using calcification for defense against UVR, indicating a trade-off in energy and resource allocation. Our results indicate the negative effects of UVR on coccolithophorid growth and photosynthesis, and highlight the important role of N availability in defense against UVR as well as high PAR. We predict that enhanced N-limitation in future surface oceans due to warming-induced stratification will exacerbate the sensitivity of G. oceanica to UVR, while coccolithophores can be potentially more susceptible to other environmental stresses due to increased levels of nutrient limitation.

Physiological Responses of Sargassum muticum, a Potential Golden Tide Species, to Different Levels of Light and Nitrogen

Sargassum golden tides have bloomed frequently in many sea areas throughout the world, and negatively impacted on the local marine ecology. Sargassum muticum commonly inhabits rocky shores. It is now distributed worldwide due to its invasiveness, and recently drifting individuals have been observed on the coasts of Canary Islands. However, as a potential golden tide alga, physiological, and ecological studies of this species have not been frequently explored. To investigate the responses of S. muticum to light and nitrogen, two key environmental factors in golden tide formation, we established three light levels (LL, low light, 10 μmol photons m–2 s–1; ML, medium light, 60 μmol photons m–2 s–1, and HL, high light, 300 μmol photons m–2 s–1) and two nitrogen levels (LN, low nitrogen, 25.0 μM of natural seawater; HN, high nitrogen, 125.0 μM), and cultivated the thalli under different conditions for 12 days before measuring the physiological properties of alga. The results showed that higher light and/or nitrogen levels enhanced the relative algal growth rate. The maximum net photosynthesis rate of alga increased with the light, while it remained unaffected by the nitrogen. The HN treatment had no effect on the apparent photosynthetic efficiency of algae in the LL culture, while increased it in the ML and HL cultures. The irradiance saturation point of photosynthesis was approximately 300 μmol photons m–2 s–1 with no significant difference among the six treatments, except for a slight increase under HLHN in contrast to the LLHN and MLLN treatments. HL treatment decreased the maximum quantum yield of photosynthesis (Fv/Fm) in both nitrogen levels. In the HN culture, ML and HL led to lower values of photoinhibition, indicating higher survivability in the alga. The HN culture led to higher nitrogen uptake but had no effects on Fv/Fm and the contents of pigments and soluble protein, regardless of culture light level. Based on these results, we speculate that drifting individuals of S. muticum would be possible to form a golden tide owing to its rapid growth rate at light level of 300 μmol photons m–2 s–1, when they encountered the sustained lower light level on the sea surface (≤300 μmol photons m–2 s–1). A high nitrogen supply caused by eutrophication of seawater might facilitate this process. Our results provide an important reference for the prediction of golden tides formed by S. muticum.

Different Photosynthetic Responses of Pyropia yezoensis to Ultraviolet Radiation Under Changing Temperature and Photosynthetic Active Radiation Regimes

Macroalgae play a crucial role in coastal marine ecosystems, but they are also subject to multiple challenges due to tidal and seasonal alterations. In this work, we investigated the photosynthetic response of Pyropia yezoensis to ultraviolet radiation (PAR: 400-700 nm; PAB: 280-700 nm) under changing temperatures (5, 10 and 15°C) and light intensities (200, 500 and 800 μmol photons m^-2  s^-1 ). Under low light intensity (200 μmol photons m^-2  s^-1 ), P. yezoensis showed the lowest sensitivity to ultraviolet radiation, regardless of temperature. However, higher temperatures inhibited the repair rates (r) and damage rates (k) of photosystem II (PSII) in P. yezoensis. However, under higher light intensities (500 and 800 μmol photons m^-2  s^-1 ), P. yezoensis showed higher sensitivity to UV radiation. Both r and the ratio of repair rate to damage rate (r:k) were significantly inhibited in P. yezoensis by PAB, regardless of temperature. In addition, higher temperatures significantly decreased the relative UV-inhibition rates, while an increased carbon fixation rate was found. Our study suggested that higher light intensities enhanced the sensitivity to UV radiation, while higher temperatures could relieve the stress caused by high light intensity and UV radiation.

UVR and PAR absorbing compounds of marine brown macroalgae along a latitudinal gradient of the Brazilian coast

Absorption spectra are indicative of biological sample chemical composition and can be used as a basis for the construction of descriptive and predictive models for biotechnological screening or assays. In marine algae, chemical composition can vary due to species-specific differences in biochemistry, as well as intra-specific responses to unique environmental variables. Different indices (UVCi, UVB+Ai and PARi) were proposed and calculated to evaluate how photoprotective compounds vary in 18 species of Phaeophyceae. In addition, they were correlated to abiotic factors. Through this technique, seven main peaks were detected in the absorbing spectra of marine brown algal extracts. The highest photoprotective indices values were found in species collected in tropical areas, where higher solar radiation is observed compared to the southern Brazilian coast. Considering additional abiotic factors, water temperature and nitrate concentration were negatively correlated with UV indices. PARi's indices were positively affected by nitrate. All species collected on the Brazilian coast have absorption peaks in the region of phenolic compounds and carotenoids, suggesting that tropical marine brown macroalgae may have developed an effective antioxidant defense system, suggesting adaptation to environments characterized by high solar radiation. UVR/PAR indices congregated essential information to possible future biotechnological screening, facilitating selection of high priority species or sites, fostering actions to enhance alternative sustainable management strategies of coastal environments.

Solar exposure(s) and facial clinical signs of aging in Chinese women: impacts upon age perception

A new reference clinical atlas of facial signs dedicated to photoaging was applied to 301 Chinese women of various ages through standardized photographs. Such approach aimed at better describing the facial changes induced by both real/chronological age and sun exposure and their respective impact on two subcohorts of different behavior with regard to sun exposure. A total of 28 various facial signs were individually graded according to their severity by a panel of experts, and a perceived apparent age of each subject was assessed. Results showed that the severity of major signs significantly increased rather linearly with age, with a higher rate in sun-exposed subjects as compared with subjects who regularly avoid sun exposure. The severity of facial signs, all impacted by sun exposure, better correlated with perceived apparent age than real/chronological age. The protocol used in the present work, similar to that previously applied to two cohorts of French women, assigned a greater impact of sun exposure in the facial aging signs of Asian women – all clinical signs are influenced by extrinsic factors – as compared with Caucasian women of comparable ages, likely related to much more intense ultraviolet (UV) radiation.

Effects of UV radiation on aquatic ecosystems and interactions with other environmental factors

Combined effects of anthropogenic changes in the environmental condition in marine ecosystems, including UV, CO₂and temperature.