Intracellular pH in Cnidarian-Dinoflagellate Symbiosis

• Main Author: Gibbin, Emma M.
• Other Authors: Davy, Simon K.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Victoria University of Wellington 2014
• Subjects: Coral; Ocean acidification; Global warming
• Online Access: http://researcharchive.vuw.ac.nz/handle/10063/3708

Accumulation of anthropogenic CO₂ is fuelling the decline of coral reef ecosystems. Increasing sea surface temperatures disrupt the endosymbiotic relationship between cnidarians and their single-celled dinoflagellate partners (genus Symbiodinium), while ocean acidification is known to impede calcification. At the cellular level, however, ocean acidification also has the potential to cause acidosis, with negative impacts on cell structure and function. Yet, despite the importance of intracellular pH (pHᵢ), the mechanisms involved in pH regulation and the buffering capacity within coral cells are not well understood. Combining pH-sensitive fluorescent dyes with either confocal microscopy or flow cytometry enables the measurement of pHᵢ within live cells. Here, I employed these techniques to determine the relationship between symbiont photosynthesis and host- and symbiont pHᵢ under ocean acidification and thermal stress. The specific aims of the study were: (1) to design a protocol for measuring the pHᵢ of the Symbiodinium cell and to quantify the effect of the diel light cycle on the pHᵢ of both members of the endosymbiosis; (2) to determine the role of the symbiont in modifying host cellular responses to short-term CO₂-induced acidification; (3) to quantify how exposure to elevated temperature changes the responses of the host and the symbiont pHᵢ to short-term CO₂-induced acidification; and (4) to establish the relationship between photo-physiology and pHᵢ after longerterm exposure to CO₂-induced acidification. In Chapter 2, I used flow cytometry in conjunction with the ratiometric fluorescent dye BCECF to quantify pHᵢ in Symbiodinium cells and to monitor the effect of the diel light/dark cycle on pHᵢ. The pHᵢ of ITS2 type B1 cells (freshly isolated from the sea anemone Aiptasia pulchella) was 7.25 ± 0.01 (mean ± S.E.M) in the light and 7.10 ± 0.02 in the dark. A comparable effect of irradiance was seen across a variety of cultured Symbiodinium genotypes (types A1, B1, E1, E2, F1, and F5) which varied between ...