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

Abstract

Microorganisms confined to annual sea ice in the Southern Ocean are exposed to highly variable oxygen and carbonate chemistry dynamics because of the seasonal increase in biomass and limited exchange with the underlying water column. For sea-ice algae, physiological stress is likely to be exacerbated when the ice melts; however, variation in carbonate speciation has rarely been monitored during this important state-transition. Using pulse amplitude modulated fluorometry (Imaging-PAM, Walz), we documented in situ changes in the maximum quantum yield of photosystem II (F v /F m) of sea-ice algae melting out into seawater with initial pH values ranging from 7.66 to 6.39. Although the process of ice-melt elevated seawater pH by 0.2-0.55 units, we observed a decrease in F v /F m between 0.02 and 0.06 for each unit drop in pH during real-time fluorescence imaging. These results are considered preliminary but provide context for including carbonate chemistry monitoring in the design of future sea ice state-transition experiments. Imaging-PAM is a reliable technology for determining F v /F m , but is of limited use for obtaining additional photosynthetic parameters when imaging melting ice.

Elevated temperature and decreased salinity both affect the biochemical composition of the Antarctic sea-ice diatom Nitzschia lecointei, but not increased pCO2

“…The constant for SO 4 − was determined by Dickson (1990) No or very minor negative effects of increased pCO 2 have previously been reported on the growth of N. lecointei at −1.8 °C (Torstensson et al 2013(Torstensson et al , 2015b, which is consistent with this study. By the end of the experiment in the present study, however, we observed a 16% increase in NPQ and a 14% increase in TBARS content at high compared to low pCO 2 , indicating that ocean acidification may lead to higher PAR sensitivity in N. lecointei, similar to that seen in natural sea-ice algal assemblages (Castrisios et al 2018) and in mesophilic diatoms (Gao et al 2012). Radiation stress can be coupled with increased lipid peroxidation in Antarctic microalgae (Buma et al 2006), which may have been coupled with a mismatch in PSII efficiency and reactive oxygen species scavenging as a result of lowered medium pH.…”

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

“…Chlorophyll a fluorescence was measured using a Maxi imaging pulse amplitude modulated fluorometer (I-PAM, Walz Germany) using the methods described by Castrisios et al (2018). Briefly, extracted ice-cores were cut into 50 × 50 × 30 mm blocks, placed in black plastic containers, and carefully aligned into position on the I-PAM stage.…”

“…Briefly, extracted ice-cores were cut into 50 × 50 × 30 mm blocks, placed in black plastic containers, and carefully aligned into position on the I-PAM stage. The saturation pulse method was then used to determine the maximum quantum yield by measuring the minimum (Fo) and maximum (Fm) fluorescence of the inverted algae biofilm in a dark-adapted state (Castrisios et al, 2018). Fv/Fm is a sensitive indicator of photosystem potential and a proxy for cellular health in photosynthetic organisms.…”

“…Environmental perturbation can influence multiple aspects of phototrophic metabolism and cause significant stress that manifests first in the photosynthetic apparatus (e.g., Murata et al, 2007;Ryan et al, 2009;Castrisios et al, 2018). While photosynthesis primarily serves to capture and convert light into cellular energy, it can also function as an efficient monitoring system for environmental change.…”

Global Changes, Anthropogenic Impacts and the Future of the Oceans

“…84 No Brasil, Kerr e colaboradores identificaram os recifes coralinos, 85 a plataforma de rodolitos (algas calcárias) ao largo dos litorais do Espírito Santo e Bahia, e as regiões de ressurgência da costa e da plataforma como áreas mais sensíveis à acidificação, apesar dos conhecimentos atuais ainda não permitirem apontar efeitos diretos. A comunidade científica brasileira é atuante neste tema através da Rede Brasileira de Pesquisa em Acidificação dos Oceanos (BrOA) 86 e vem abordando o tema no sentido de melhorar a qualidade dos dados observacionais com protocolos adotados internacionalmente, 85,87 através de experimentos com organismos para entender a resposta à acidificação [88][89][90][91] e estudos de observação na plataforma e áreas oceânicas (e.g. 92,93 ) especialmente no que diz respeito à porção oeste do Oceano Atlântico Equatorial e Sul.…”