Rapid Manipulation in Irradiance Induces Oxidative Free-Radical Release in a Fast-Ice Algal Community (McMurdo Sound, Antarctica)

Sea ice supports a unique assemblage of microorganisms that underpin Antarctic coastal food-webs, but reduced ice thickness coupled with increased snow cover will modify energy flow and could lead to photodamage in ice-associated microalgae. In this study, microsensors were used to examine the influence of rapid shifts in irradiance on extracellular oxidative free radicals produced by sea-ice algae. Bottom-ice algal communities were exposed to one of three levels of incident light for 10 days: low (0.5 μmol photons m−2 s−1, 30 cm snow cover), mid-range (5 μmol photons m−2 s−1, 10 cm snow), or high light (13 μmol photons m−2 s−1, no snow). After 10 days, the snow cover was reversed (either removed or added), resulting in a rapid change in irradiance at the ice-water interface. In treatments acclimated to low light, the subsequent exposure to high irradiance resulted in a ~400× increase in the production of hydrogen peroxide (H2O2) and a 10× increase in nitric oxide (NO) concentration after 24 h. The observed increase in oxidative free radicals also resulted in significant changes in photosynthetic electron flow, RNA-oxidative damage, and community structural dynamics. In contrast, there was no significant response in sea-ice algae acclimated to high light and then exposed to a significantly lower irradiance at either 24 or 72 h. Our results demonstrate that microsensors can be used to track real-time in-situ stress in sea-ice microbial communities. Extrapolating to ecologically relevant spatiotemporal scales remains a significant challenge, but this approach offers a fundamentally enhanced level of resolution for quantifying the microbial response to global change.

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Mycosporine-Like Amino Acids in Antarctic Sea Ice Algae, and Their Response to UVB Radiation

Zeitschrift für Naturforschung C ◽

10.1515/znc-2002-5-612 ◽

2002 ◽

Vol 57 (5-6) ◽

pp. 471-477 ◽

Cited By ~ 27

Author(s):

Ken G Ryan ◽

Andrew McMinn ◽

Kevin A. Mitchell ◽

Louise Trenerry

Keyword(s):

Amino Acids ◽

Sea Ice ◽

Uv Radiation ◽

Algal Community ◽

Minor Role ◽

Ice Algae ◽

Uvb Radiation ◽

Visible Radiation ◽

Degree Of Protection ◽

Sea Ice Algae

Mycosporine like amino acids (MAAs) were detected in low concentration in sea ice algae growing in situ at Cape Evans, Antarctica. Four areas of sea ice were covered with plastics of different UV absorption exposing the bottom- ice algal community to a range of UV doses for a period of 15 days. Algae were exposed to visible radiation only; visible + UV radiation; and visible + enhanced UV radiation. MAA content per cell at the start of the experiment was low in snow-covered plots but higher in samples from ice with no snow cover. During the study period, the MAA content per cell reduced in all treatments, but the rate of this decline was less under both ambient UV and visible radiation than under snow covered plots. While low doses of UVB radiation may have stimulated some MAA production (or at least slowed its loss), relatively high doses of UVB radiation resulted in almost complete loss of MAAs fromice algal cells. Despite this reduction in MAA content per cell, the diatoms in all samples grew well, and there was no discernible effect on viability. This suggests that MAAs may play a minor role as photoprotectants in sea ice algae. The unique structure of the bottom ice algal community may provide a self-shading effect such that algal cells closest to the surface of the ice contain more MAAs than those below them and confer a degree of protection on the community as a whole.

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Upwelling Irradiance below Sea Ice—PAR Intensities and Spectral Distributions

Journal of Marine Science and Engineering ◽

10.3390/jmse9080830 ◽

2021 ◽

Vol 9 (8) ◽

pp. 830

Author(s):

Lars Chresten Lund-Hansen ◽

Michael Bjerg-Nielsen ◽

Tanja Stratmann ◽

Ian Hawes ◽

Brian K. Sorrell

Keyword(s):

Sea Ice ◽

Snow Cover ◽

Daily Maximum ◽

First Year ◽

Ice Algae ◽

Sea Ice Algae ◽

Spectral Distributions ◽

And Performance ◽

Light Saturation Point ◽

Upwelling And Downwelling

Upwelling and downwelling spectral (320–920 nm) distributions and photosynthetic active radiation (PAR) intensities were measured below a first-year land-fast sea ice in a western Greenland fjord with and without a snow cover. Time-series of surface upwelling PAR, downwelling PAR, and under-ice PAR were also obtained. Spectral distributions of upwelling and downwelling irradiances were similar except for reduced intensities in the UV, the red, and NIR parts of the spectrum when the ice was snow-covered. Upwelling PAR amounted to about 10% of downwelling intensities, giving 5.1 µmol photons m−2 s−1 at the bottom of the ice with a snow cover and 8.2 µmol photons m−2 s−1 without. PAR partitioning analyses showed that the upwelling was related to scattering by suspended particles in the water column. A snow melt increased under-ice daily maximum downwelling PAR from 50 to 180 µmol photons m−2 s−1 and overall under-ice PAR of 55 and 198 µmol photons m−2 s−1 with 10% upwelling. It is concluded that upwelling PAR below sea ice might be an important factor regarding sea ice algae photophysiology and performance with a 10% higher PAR; specifically when PAR > Ek the light saturation point of the sea ice algae.

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Low Fe Availability for Photosynthesis of Sea-Ice Algae: Ex situ Incubation of the Ice Diatom Fragilariopsis cylindrus in Low-Fe Sea Ice Using an Ice Tank

Frontiers in Marine Science ◽

10.3389/fmars.2021.632087 ◽

2021 ◽

Vol 8 ◽

Author(s):

Kazuhiro Yoshida ◽

Andreas Seger ◽

Matthew Corkill ◽

Petra Heil ◽

Kristen Karsh ◽

...

Keyword(s):

Sea Ice ◽

High Light ◽

Freezing Stress ◽

Ex Situ ◽

Ice Algae ◽

Light Conditions ◽

Low Light ◽

Ice Melt ◽

Sea Ice Algae ◽

Fragilariopsis Cylindrus

Sea-ice algae play a crucial role in the ecology and biogeochemistry of sea-ice zones. They not only comprise the base of sea-ice ecosystems, but also seed populations of extensive ice-edge blooms during ice melt. Ice algae must rapidly acclimate to dynamic light environments, from the low light under sea ice to high light within open waters. Recently, iron (Fe) deficiency has been reported for diatoms in eastern Antarctic pack ice. Low Fe availability reduces photosynthetic plasticity, leading to reduced ice-algal primary production. We developed a low-Fe ice tank to manipulate Fe availability in sea ice. Over 20 days in the ice tank, the Antarctic ice diatom Fragilariopsis cylindrus was incubated in artificial low-Fe sea ice ([total Fe] = 20 nM) in high light (HL) and low light (LL) conditions. Melted ice was also exposed to intense light to simulate light conditions typical for melting ice in situ. When diatoms were frozen in, the maximum photochemical quantum efficiency of photosystem II (PSII), Fv/Fm, was suppressed by freezing stress. However, the diatoms maintained photosynthetic capability throughout the ice periods with a stable Fv/Fm value and increased photoprotection through non-photochemical quenching (NPQ) via photoprotective xanthophyll cycling (XC) and increased photoprotective carotenoid levels compared to pre-freeze-up. Photoprotection was more pronounced in the HL treatment due to greater light stress. However, the functional absorption cross section of PSII, σPSII, in F. cylindrus consistently increased after freezing, especially in the LL treatment (σPSII > 10 nm2 PSII–1). Our study is the first to report such a large σPSII in ice diatoms at low Fe conditions. When the melted sea ice was exposed to high light, Fv/Fm was suppressed. NPQ and XC were slightly upregulated, but not to values normally observed when Fe is not limiting, which indicates reduced photosynthetic flexibility to adapt to environmental changes during ice melt under low Fe conditions. Although ice algae can optimize their photosynthesis to sea-ice environments, chronic Fe starvation led to less flexibility of photoacclimation, particularly in low light conditions. This may have detrimental consequences for ice algal production and trophic interactions in sea-ice ecosystems if the recent reduction in sea-ice extent continues.

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Effects of increased irradiance on biomass, photobiology, nutritional quality, and pigment composition of Arctic sea ice algae

Marine Ecology Progress Series ◽

10.3354/meps13411 ◽

2020 ◽

Vol 648 ◽

pp. 95-110 ◽

Cited By ~ 3

Author(s):

LC Lund-Hansen ◽

I Hawes ◽

K Hancke ◽

N Salmansen ◽

JR Nielsen ◽

...

Keyword(s):

Sea Ice ◽

Primary Production ◽

Snow Cover ◽

Nutritional Quality ◽

Light Availability ◽

Arctic Sea Ice ◽

The Arctic ◽

Ice Algae ◽

Sea Ice Algae ◽

Arctic Sea

Ice algae are key contributors to primary production and carbon fixation in the Arctic, and light availability is assumed to limit their growth and productivity. We investigated photo-physiological responses in sea ice algae to increased irradiance during a spring bloom in West Greenland. During a 14 d field experiment, light transmittance through sea ice was manipulated to provide 3 under-ice irradiance regimes: low (0.04), medium (0.08), and high (0.16) transmittances. Chlorophyll a decreased with elevated light availability relative to the control. Maximum dark-adapted photosynthetic efficiency (ΦPSII_max) showed an initially healthy and productive ice algae community (ΦPSII_max > 0.6), with ΦPSII_max decreasing markedly under high-light treatments. This was accompanied by a decrease in the light utilization coefficient (α) and photosynthetic capacity (maximum relative electron transfer rate), and a decrease in the ratio of mono- to polyunsaturated fatty acids. This was partly explained by a corresponding increase of photoprotective pigments (diadinoxanthin and diatoxanthin), and a development of mycosporine-like amino acids as identified from a distinctive spectral absorption peak at 360 nm. After 14 d, in situ fluorescence imaging revealed significant differences in ΦPSII_max between treatments of dark-adapted cells (i.e. those sampled before sunrise and after sunset), during diel cycles, with clear chronic photoinhibition in high and medium treatments. Data demonstrate the high sensitivity of spring-blooming Arctic sea ice algae to elevated irradiance caused by loss of snow cover. The predicted loss of snow cover on landfast ice will negatively impact ice algae, their potential primary production, and nutritional quality for higher trophic levels.

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