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Brown University

Publication Date

Fall 2018

Program Name

Australia: Rainforest, Reef, and Cultural Ecology


Crustose Coralline Algae (CCA) are prolific reef builders and primary producers that play a key role in maintaining the structural integrity of coral reef systems (Littler and Littler, 2013). They are also highly important in increasing reef resilience by serving as a substrate for the recruitment and metamorphosis of coral larvae (Chisholm, 2000). Little is known about the way in which increasing seawater temperatures due to climate change might affect metabolic rates like photosynthesis in CCA. Therefore, a study was carried out in November, 2018, in the lab at Lizard Island Research Station to explore the photosynthetic performance of a species of CCA across a range of temperatures.

Photosynthesis and respiration rates for Porolithon sp., a particularly ubiquitous species of CCA among the coral reefs surrounding Lizard Island, were determined at six distinct incubation temperatures (22°C, 24°C, 26°C, 28°C, 30°C, and 32°C). Net photosynthesis was found to be the highest at 26°C, close to the 27°C annual average water temperature at Lizard Island (Daily Average Ocean Water Temperatures, 2018). Net respiration was found to be greatest at 28°C and gross photosynthesis was found to be greatest at 26°C. A 26% decrease in net photosynthesis and a 24% decrease in gross photosynthesis were observed from the determined optimal temperature (26°C) to the upper limit of the study (32°C). With increasing temperature (1ºC / hr.), net photosynthesis was found to decrease as temperature increased, reducing to a value of zero μmol O2 cm-2 hr-1 at 34°C. The significant decrease in primary productivity of Porolithon sp. observed in both assays suggests that projected elevation in seawater temperatures will likely negatively affect the primary productivity and fitness of CCA, which may have serious implications for its surrounding community.

Keywords: Crustose Coralline Algae, Porolithon sp., Photosynthesis, Respiration, Thermal Stress


Biology | Other Life Sciences | Plant Sciences



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