Ocean Acidification: Comparative Impacts on the Photophysiology of a Temperate Symbiotic Sea Anemone and a Tropical Coral

• Main Author: Doherty, Michael
• Format: Thesis
• Language: unknown
• Published: 2009
• Subjects: Physical Geography and Environmental Geoscience not elsewhere classified; Ocean acidification; Symbiosis; Photosynthesis; School: School of Biological Sciences; 040699 Physical Geography and Environmental Geoscience not elsewhere classified; Marsden: 260401 Biological Oceanography; Degree Discipline: Marine Biology; Degree Level: Masters; Degree Name: Master of Science; Marsden
• Online Access: https://doi.org/10.26686/wgtn.16970062; https://figshare.com/articles/thesis/Ocean_Acidification_Comparative_Impacts_on_the_Photophysiology_of_a_Temperate_Symbiotic_Sea_Anemone_and_a_Tropical_Coral/16970062

Ocean acidification has the potential to drastically alter the coral reef ecosystem by reducing the calcification rate of corals and other reef-builders, and hence a considerable amount of research is now focused on this issue. It also is conceivable that acidification may affect other physiological processes of corals. In particular, acidification may alter photosynthetic physiology and hence the productivity of the coraldinoflagellate symbiosis that is pivotal to the reef's survival and growth. However, very little is known about the impacts of acidification on the photophysiology of corals or, indeed, other invertebrate-algal symbioses. This gap in our knowledge was addressed here by measuring the impacts of acidification (pH 7.6 versus pH 8.1) on the photophysiology and health of the tropical coral Stylophora pistillata and its isolated dinoflagellate symbionts ('zooxanthellae'), and the temperate sea anemone Anthopleura aureoradiata. The comparative nature of this study allowed for any differences between tropical and temperate symbioses, and zooxanthellae in a symbiotic or free-living state, to be assessed. Corals, anemones and cultured zooxanthellae were maintained in flowthrough seawater systems, and treated either with non-acidified (control) seawater at pH 8.1, or seawater acidified with CO2 or HCl to pH 7.6. A variety of parameters, including zooxanthellar density, chlorophyll content, photosynthetic health (Yi), and the ratio of gross photosynthetic production to respiration (P:R) were measured via cell counts, spectrophotometry, respirometry and PAM fluorometry, at a series of time-points up to a maximum of 42 days. Acidification generated by the addition of CO2 had no discernible effect on Yi of either the corals or anemones. However, in the coral, chlorophyll content per zooxanthella cell increased by 25%, which was countered by a near-significant decline (22%) in the rate of gross photosynthesis per unit chlorophyll; as zooxanthellar density remained unchanged, this led to a constant P:R ratio. ...