The influence of increased temperature and carbon dioxide levels on the benthic/sea ice diatom Navicula directa

Polar oceans are very susceptible to increased levels of atmospheric CO2 and may act as the world's largest sink for anthropogenic CO2. Simultaneously, as atmospheric CO2 increases, sea surface temperature rises due to global warming. These two factors are important in regulating microalgal ecophysiology, and it has been suggested that future global changes may significantly alter phytoplankton species composition. This study aims to investigate potential consequences of global change in terms of increased temperature and CO2 enrichment on the benthic/sea ice diatom Navicula directa. In a laboratory experiment, the physiological response to elevated temperature and partial pressure of CO2 (pCO(2)) was investigated in terms of growth, photosynthetic activity and photosynthetic pigment composition. The experiment was performed under manipulated levels of pCO(2) (380 and 960 ppm) and temperature (0.5 and 4.5A degrees C) to simulate a change from present levels to predicted levels during a worst-case scenario by the year 2100. After 7 days of treatment, no synergetic effects between temperature and pCO(2) were detected. However, elevated temperature promoted effective quantum yield of photosynthesis (Delta F/F'(m)) and increased growth rates by approximately 43%. Increased temperature also resulted in an altered pigment composition. In addition, enrichment of CO2 appeared to reduce specific growth rates of N. directa. Even though growth rates were only reduced by approximately 5%, we hereby report that increased pCO(2) levels might also have potential negative effects on certain diatom strains.