Jurriaans, Saskia, Hoogenboom, Mia O., and Ferrier-Pages, Christine (2021) Similar thermal breadth of two temperate coral species from the Mediterranean Sea and two tropical coral species from the Great Barrier Reef. Coral Reefs, 40 (4). pp. 1281-1295.

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Abstract

Temperate organisms are generally exposed to a more variable and cooler climate than tropical organisms, and are therefore expected to have broader thermal tolerance and a different thermal performance curve. This study investigated these hypotheses by comparing the thermal performance of two common tropical coral species found in the Great Barrier Reef with the two most common temperate coral species from the Mediterranean Sea. Photosynthesis rates, dark respiration rates, maximum PSII quantum yield (Fv/Fm) and electron transport rates (rETRm) were measured on coral fragments exposed to an acute temperature increase and decrease up to 5 °C above and below the average environmental seawater temperature. Dark respiration rates and Fv/Fm increased linearly with temperature, suggesting broad thermal tolerance. For photosynthesis and rETRm, the performance breadths were surprisingly similar between the tropical and temperate species. However, the thermal optimum for performance was generally below the local average temperature, and only coincided with the prevailing environmental temperature for one of the tropical species. The broad thermal tolerance for photosynthesis displayed in this study supports previous observations that corals can survive short periods of abnormally warm temperatures and suggests that corals adopt thermal generalist strategies to cope with temperature variation in the environment. Nevertheless, current mean temperatures are 10–30% above the thermal optimum for the species studied here, demonstrating that conditions are already pushing the boundaries of coral thermal tolerance.

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