Can bottom ice algae tolerate irradiance and temperature changes?

Abstract

Sea ice algae are significant primary producers of the ice-covered marine environment, growing under typically cold, dim conditions. During ice break-up they are released to the water column, where temperatures can be several degrees higher and irradiance can increase by orders of magnitude. To determine how sea ice algae respond to such rapid changes, we carried out incubations to examine their tolerance to environmentally realistic levels of change in temperature and PAR, as expressed by photosynthetic response and production of mycosporine-like amino acids (MAAs). The algae were also exposed to a broader range of temperatures, to evaluate their potential to function in warmer seas in the event, for instance, of anthropogenic transfer to locations further north. When subjected to PAR (0-100 μmol m −2 s −1 ) at ecologically relevant temperatures (− 1°C, 2°C, 5°C), the algae showed tolerance, indicated by a lack of decline in the quantum efficiency of photosystem II (PSII). The data show that bottom ice algae can tolerate increasing temperature and PAR comparable to the changes experienced during and after sea ice melt. MAA production increased at higher PAR and temperature. At ambient PAR levels, increased temperatures resulted in lower ϕ PSII . However, as PAR levels were increased, higher temperature reduced the level of stress as indicated by higher ϕ PSII values. This result suggests, for the first time in sea ice algal studies, that higher temperatures can ameliorate the negative effects of increased PAR. Exposure to much higher temperatures suggested that the algae were capable of retaining some photosynthetic function at water temperatures well above those currently experienced in some of their Antarctic habitats. However, when temperature was gradually increased past 14°C, the photosystems started to become inactivated as indicated by a decrease in quantum yield, suggesting that the algae would not be viable if transferred to lower latitude cold temperate areas.

Response of Antarctic sea-ice algae to an experimental decrease in pH: a preliminary analysis from chlorophyll fluorescence imaging of melting ice

“…The relative change in F v /F m described by the model must be considered a subtle trend, but it is potentially indicative of a more significant stress response had the experiment been conducted over a longer time period. Importantly, we did not observe a threshold at which point algal photophysiology is compromised to the extent observed when other stressors such as light (Ralph et al 2007;Ryan et al 2009;Ryan et al 2011), temperature Rajanahally et al 2014) or salinity (Ryan et al 2004;Ralph et al 2007;Ryan et al 2011) are manipulated.…”

Increased temperature benefits growth and photosynthetic performance of the sea ice diatom Nitzschia cf. neglecta (Bacillariophyceae) isolated from saroma lagoon, Hokkaido, Japan

“…, Rajanahally et al. ). Such large variations of light and temperature are likely to influence photophysiological performance of ice algae, where species with greater flexibility in photoacclimation are afforded a higher chance of survival.…”

“…Although ice algae are unlikely to experience temperatures significantly above the melting point of the sea ice matrix, they may be exposed to temperatures that are several degrees higher in surface seawater. At the same time, irradiance levels can be orders of magnitude higher at the surface than under the ice (Fiala and Oriol 1990, R o_ za nska et al 2009, Rajanahally et al 2014. Such large variations of light and temperature are likely to influence photophysiological performance of ice algae, where species with greater flexibility in photoacclimation are afforded a higher chance of survival.…”

Aspects of resilience of polar sea ice algae to changes in their environment

“…obs. ; see also Rajanahally et al, 2014) and are representative of the PAR and UV-B levels that sea ice algae would be exposed to from the middle to the bottom of the sea ice profile (Eicken, 1992;Rajanahally et al, 2014;Ryan et al, 2011). Sub-samples (400 ml) of monospecific cultures (n=3 at each level) were incubated under each of four light levels (L0=0 mol m -2 s -1 , L1=1 mol m -2 s -1 of PAR, L2=45 mol m -2 s -1 of PAR and mW m -2 of UV-B, L3=100 mol m -2 s -1 of PAR and 50 mW m -2 of UV-B) at 4°C for 168 h in a temperature controlled water bath (Haake, Cleveland, OH, USA).…”

“…Samples of 1 ml for cell counts were taken at 0, 48 and 168 h from all replicates in each incubation, preserved using 2% Lugol's Iodine and stored at 4°C. Fifty ml of sample was used for the measurement of MAA content following the protocol described by Ryan et al (2002) and Rajanahally et al (2014). However, as no detectable amounts of MAAs were produced, no further consideration of MAAs is included here.…”