Publication Date:
2024-03-15
Description:
The effects of elevated CO2 and temperature on photosynthesis and calcification of two important calcifying reef algae (Halimeda macroloba and Halimeda cylindracea) were investigated with O2 microsensors and chlorophyll a fluorometry through a combination of two pCO2 (400 and 1,200 µatm) and two temperature treatments (28 and 32 °C) equivalent to the present and predicted conditions during the 2100 austral summer. Combined exposure to pCO2 and elevated temperature impaired calcification and photosynthesis in the two Halimeda species due to changes in the microenvironment around the algal segments and a reduction in physiological performance. There were no significant changes in controls over the 5-week experiment, but there was a 50-70 % decrease in photochemical efficiency (maximum quantum yield), a 70-80 % decrease in O2 production and a threefold reduction in calcification rate in the elevated CO2 and high temperature treatment. Calcification in these species is closely coupled with photosynthesis, such that a decrease in photosynthetic efficiency leads to a decrease in calcification. Although pH seems to be the main factor affecting Halimeda species, heat stress also has an impact on their photosystem II photochemical efficiency. There was a strong combined effect of elevated CO2 and temperature in both species, where exposure to elevated CO2 or temperature alone decreased photosynthesis and calcification, but exposure to both elevated CO2 and temperature caused a greater decline in photosynthesis and calcification than in each stress individually. Our study shows that ocean acidification and ocean warming are drivers of calcification and photosynthesis inhibition in Halimeda. Predicted climate change scenarios for 2100 would therefore severely affect the fitness of Halimeda, which can result in a strongly reduced production of carbonate sediments on coral reefs under such changed climate conditions.
Keywords:
Alkalinity, total; Alkalinity, total, standard error; Aragonite saturation state; Aragonite saturation state, standard error; Benthos; Bicarbonate ion; Bicarbonate ion, standard error; Calcite saturation state; Calculated using CO2SYS; Calculated using seacarb after Nisumaa et al. (2010); Carbon, inorganic, dissolved; Carbon, inorganic, dissolved, standard error; Carbonate ion; Carbonate ion, standard error; Carbonate system computation flag; Carbon dioxide; Carbon dioxide, standard error; Chlorophyta; Coast and continental shelf; Containers and aquaria (20-1000 L or 〈 1 m**2); Distance; Effective quantum yield; Effective quantum yield, standard error; Excitation pressure; Excitation pressure, standard error; Figure; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Gross photosynthesis rate, oxygen; Gross photosynthesis rate, oxygen, standard error; Halimeda cylindracea; Halimeda macroloba; Heron_Reef; Heron Reef, Great Barrier Reef, Queensland; Incubation duration; Irradiance; Laboratory experiment; Macroalgae; Maximum photochemical quantum yield of photosystem II; Maximum photochemical quantum yield of photosystem II, standard error; OA-ICC; Ocean Acidification International Coordination Centre; Oxygen; Oxygen, flux, diffusive; Oxygen, flux, diffusive, standard error; Oxygen, standard error; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Partial pressure of carbon dioxide (water) at sea surface temperature (wet air), standard error; pH; Plantae; Potentiometric; Potentiometric titration; Primary production/Photosynthesis; Salinity; Single species; South Pacific; Species; Temperate; Temperature; Temperature, water; Treatment
Type:
Dataset
Format:
text/tab-separated-values, 51002 data points
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