Abstract
Ultraviolet-B (UVB) radiation is a global stressor that has profound impacts on freshwater and marine ecosystems. However, an analysis of the patterns of sensitivity to UVB radiation across aquatic photosynthetic organisms has not yet been published. Here, we performed a meta-analysis on results reported in 214 studies compiled from the published literature to quantify and compare the magnitude of responses of aquatic photosynthetic organisms to changes in UVB radiation. The meta-analysis was conducted on observations of marine (n = 893) and freshwater macroalgae (n = 126) and of marine (n = 1087) and freshwater (n = 2889) microalgae (total n = 4995). Most of these studies (85%) analysed the performance of organisms exposed to natural solar radiation when UVB was partially or totally reduced compared with the organismal performance under the full solar radiation spectrum, whereas the remaining 15% of the studies examined the responses of organisms to elevated UVB radiation mostly using artificial lamps. We found that marine photosynthetic organisms tend to be more sensitive than freshwater photosynthetic organisms to UVB radiation; responses to either decreased or increased UVB radiation vary among taxa; the mortality rate is the most sensitive of the trait responses to elevated UVB radiation, followed by changes in cellular and molecular traits; the sensitivity of microalgae to UVB radiation is dependent on size, with small-celled microalgae more sensitive than large-celled microalgae to UVB radiation. Thick macroalgae morphotypes were the less sensitive to UVB, but this effect could not be separated from phylogenetic differences. The high sensitivity of marine species, particularly the smallest photosynthetic organisms, to increased UVB radiation suggests that the oligotrophic ocean, a habitat comprising 70 % of the world’s oceans with high UVB penetration and dominated by picoautotrophs, is extremely vulnerable to changes in UVB radiation.
Highlights
The increased use of chlorofluorocarbons (CFCs) as refrigerants and propellants led to an alarming depletion of stratospheric ozone in the 1980s (Molina and Rowland, 1974) and to a corresponding increase in ultraviolet-B (UVB) radiation reaching the Earth’s surface (Madronich et al, 1998)
Studies were selected when they met the following criteria outlined by Llabrés et al (2013): (1) include assessments of the performance of aquatic microalgae and macroalgae under ambient irradiance levels, (2) report a treatment corresponding to the ambient solar radiation, and (3) include additional treatments by either removing or enhancing UVB radiation relative to ambient levels [e.g., control: photosynthetic active radiation (PAR) + ultraviolet-A (UVA) + UVB, treatment: PAR+UVA]
It has been documented that photosynthetic organisms are, on average, more resistant to UVB radiation than other marine organisms in general (Llabrés et al, 2013)
Summary
The increased use of chlorofluorocarbons (CFCs) as refrigerants and propellants led to an alarming depletion of stratospheric ozone in the 1980s (Molina and Rowland, 1974) and to a corresponding increase in ultraviolet-B (UVB) radiation reaching the Earth’s surface (Madronich et al, 1998). The Montreal Protocol led to a dramatic reduction in the emissions of CFCs. Impacts of UVB on Aquatic Photosynthetic Organisms (UNEP, Environmental Effects Assessment Panel, 2010), the ozone layer will likely not recover to 1980 levels within the coming decades (Weatherhead and Andersen, 2006). Increased UVB radiation will continue to reach the biosphere over the coming years (Weatherhead and Andersen, 2006), the healing of Antarctic ozone layer is occurring since 2000 (Solomon et al, 2016). Increased UVB radiation has profound impacts on terrestrial and aquatic organisms (Caldwell et al, 1998; Häder et al, 2007). A meta-analysis of experimental results showed that the mortality rates of marine biota increased rapidly in response to increased UVB radiation, with protists, corals, crustaceans, fish eggs, and larvae the most sensitive in marine ecosystems to increased UVB radiation (Llabrés et al, 2013)
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