Meeting Abstract
Increasing sea surface temperatures precipitated by rising atmospheric carbon dioxide pose the greatest threat to coral reefs, as prolonged thermal stress causes coral bleaching—the breakdown of the symbiotic relationship between the coral host and its algae (Symbiodiniaceae). Predictions of the likelihood and extent of bleaching have typically considered the duration and magnitude of elevated temperatures relative to a locally defined threshold. However, recent work suggests that heterogeneity in coral bleaching patterns may be better explained by the degree of diel temperature variation typical on a given reef. Here, we conducted a 50-day common garden experiment to assess the influence of low, moderate, and high (2, 3, and 4 °C, respectively) diel temperature variation on the growth and performance of the thermally tolerant, reef-building coral Siderastrea siderea. Corals were sourced from six sites differing in thermal regime, light availability, and reef zone in Bocas del Toro, Panama. We found that corals from more thermally variable sites calcified at higher rates when compared to those from less variable sites, regardless of experimental treatment, suggesting that a history of exposure to large and frequent fluctuations in temperature enhances coral growth. Overall, corals subjected to moderate (3 °C) diel temperature variation had the highest symbiont densities and corals in the high variability treatment (4 °C) had the highest growth rates, suggesting that short term exposure to diel temperature variation may also facilitate enhanced growth and symbiosis. Our data support the hypothesis that diel thermal variation on the coral’s native reef may play a central role in susceptibility to thermal stress.
