Meeting Abstract
Corals native to variable thermal environments often resist bleaching temperatures and survive exposures that typically bleach conspecifics from cooler environments; providing promising evidence for the persistence of reefs under projected global climate change. This bleaching resistance is attributed to acclimatory or adaptive conditioning to frequent sub-lethal water temperatures. Acclimatization plays an important role in modifying thermal thresholds and has been observed within 1 week and up to 2 years in Acropora corals. However, it is not known how many species are capable of thermal acclimatization. From 2015-16, populations of two massive corals, Porites lobata and Goniastrea retiformis, were transplanted from three contrasting backreefs in Ofu Island, American Samoa, into a highly variable (HV) pool known to elicit increased bleaching tolerance. Following one week, six, and twelve months, transplanted and native coral samples were exposed to a controlled acute thermal stress assay. Physiological bleaching responses – chlorophyll concentration and photosynthetic efficiency – were quantified to characterize heat stress responses. For both species, corals transplanted into the HV pool had reduced photochemistry and pigment. Variation in thermal tolerance was instead driven by native backreef, not acclimatization or genomic differences. Moreover, comparisons of HV coral growth and bleaching response data suggest trade-offs in fitness versus stress tolerance. Summer temperatures of 2016 surpassed regional records, and HV pool variability increased in magnitude, potentially reaching local stress thresholds. This study strongly contrasts previous research conducted in the Ofu pools, indicating that distinct coral species use fundamentally different strategies to respond to and resist thermal stress.
