Physiological response of an Antarctic cryptophyte to increasing temperature, CO₂, and irradiance

Abstract

The Southern Ocean, a globally important CO2 sink, is one of the most susceptible regions in the world to climate change. Phytoplankton of the coastal shelf waters around the Western Antarctic Peninsula have been experiencing rapid warming over the past decades and current ongoing climatic changes will expose them to ocean acidification and high light intensities due to increasing stratification. We conducted a multiple‐stressor experiment to evaluate the response of the still poorly studied key Antarctic cryptophyte species Geminigera cryophila to warming in combination with ocean acidification and high irradiance. Based on the thermal growth response of G. cryophila, we grew the cryptophyte at suboptimal (2°C) and optimal (4°C) temperatures in combination with two light intensities (medium light: 100 μmol photons m−2 s−1 and high light [HL]: 500 μmol photons m−2 s−1) under ambient (400 μatm pCO2) and high pCO2 (1000 μatm pCO2) conditions. Our results reveal that G. cryophila was not susceptible to high pCO2, but was strongly affected by HL at 2°C, as both growth and carbon fixation were significantly reduced. In comparison, warming up to 4°C stimulated the growth of the cryptophyte and even alleviated the previously observed negative effects of HL at 2°C. When grown, however, at temperatures above 4°C, the cryptophyte already reached its maximal thermal limit at 8°C, pointing out its vulnerability toward even higher temperatures. Hence, our results clearly indicate that warming and high light and not pCO2 control the growth of G. cryophila.

Sentinel protist taxa of the McMurdo Dry Valley lakes, Antarctica: a review

“…However, in the presence of high CO 2 (a condition associated with ocean acidification), this light sensitivity phenotype was alleviated. Growth of G. cryophila was also stimulated under warming temperatures (Camoying and Trimborn, 2023). The conditions of higher and variable light combined with warmer temperatures and high CO 2 match climate-driven changes in the WAP.…”

“…Cryptomonad isolates from the MDV lakes are currently unavailable and so detailed knowledge of their physiology and response to varying environmental conditions is limited. A closely related isolate Geminigera cryophila, has been studied for several years and has yielded significant information regarding its ability to acclimate to a number of environmental variables (Trimborn et al, 2019;Camoying and Trimborn, 2023). These studies have revealed that the marine cryptophyte exhibits physiological plasticity to respond to variations in temperature and light.…”