title: Photosynthetic response of Persian Gulf acroporid corals to summer versus winter temperature deviations.
abstract: With on-going climate change, coral susceptibility to thermal stress constitutes a central concern in reefconservation. In the Persian Gulf, coral reefs are confronted with a high seasonal variability in water temperature, and both hot and cold extremes have been associated with episodes of coral bleaching and mortality. Using physiological performance as a measure of coral health, we investigated the thermal susceptibility of the common acroporid, Acropora downingi, near Hengam Island where the temperature oscillates seasonally in the range 20.2-34.2 °C. In a series of two short-term experiments comparing coral response in summer versus winter conditions, we exposed corals during each season (1) to the corresponding seasonal average and extreme temperature levels in a static thermal environment, and (2) to a progressive temperature deviation from the annual mean toward the corresponding extreme seasonal value and beyond in a dynamic thermal environment. We monitored four indictors of coral physiological performance: net photosynthesis (Pn), dark respiration (R), autotrophic capability (Pn/R), and survival. Corals exposed to warming during summer showed a decrease in net photosynthesis and ultimately died, while corals exposed to cooling during winter were not affected in their photosynthetic performance and survival. Coral autotrophic capability Pn/R was lower at the warmer thermal level within eachseason, and during summer compared to winter. Corals exposed to the maximum temperature of summer displayed Pn/R < 1, inferring that photosynthetic performance could not support basal metabolic needs under this environment. Our results suggest that the autotrophic performance of the Persian Gulf A. downingi is sensitive to the extreme temperatures endured in summer, and therefore its populations may be impacted by future increases in water temperature.
authors.affiliation: Iranian National Institute for Oceanography and Atmospheric Science , Tehran , Iran.
authors.forename: Jahangir
authors.initials: J
authors.lastname: Vajed Samiei
authors.affiliation: Iranian National Institute for Oceanography and Atmospheric Science , Tehran , Iran.
authors.forename: Abolfazl
authors.initials: A
authors.lastname: Saleh
authors.affiliation: Iranian National Institute for Oceanography and Atmospheric Science , Tehran , Iran.
authors.forename: Ali
authors.initials: A
authors.lastname: Mehdinia
authors.affiliation: Iranian National Institute for Oceanography and Atmospheric Science , Tehran , Iran.
authors.forename: Arash
authors.initials: A
authors.lastname: Shirvani
authors.affiliation: Bren School of Environmental Science and Management, University of California , Santa Barbara, CA , USA.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Kayal
keywords: Coral reefs; Global warming; Seasonal performance; Thermal tolerance