CHANGES IN SEASONAL CALCIFICATION AND PHOTOSYNTHESIS RATES OF REEF-BUILDING CORALS FOLLOWING A LEGACY OF REPEATED HEAT STRESS

Successive marine heatwaves are devastating reef-building corals worldwide. The long-term survival of coral populations facing these extreme events alongside chronic ocean warming may hinge on the acclimatization capacity of individual survivors. Here, we characterized the seasonal thermal performance of colonies of two Hawaiian coral species that survived the three most recent marine heatwaves in this region (2014, 2015 and 2019). These corals had distinct bleaching histories, with half bleaching and the other half remaining pigmented during prior heatwaves. Corals were assessed for seasonal calcification, photosynthesis, and respiration rates for two consecutive non-heatwave years beginning in 2023. In addition, acute thermal performance curves were performed for each individual to assess the optimal temperatures for coral growth and metabolism. Calcification and metabolic rates were indistinguishable between bleaching-resistant and bleaching-susceptible conspecifics within each season for both species, indicating metabolic recovery of the previously bleached individuals. Surprisingly, rates during the warmest time of the year were as low as the coldest time of year, despite a thermal optimum for both species above ambient summer temperatures. These declines from a late spring maximum indicate that metabolic rates may be suppressed in all individuals by late summer. Interestingly, corals with a history of bleaching had lower peak photosynthesis rates than corals that did not previously bleach, indicating persistent differences in symbiont but not host physiology.

Presentation Preference: Oral

Primary Presenter: Katie Barott, University of Pennsylvania (kbarott@sas.upenn.edu)

Authors:

Katie Barott, University of Pennsylvania  (kbarott@sas.upenn.edu)

Kristen Brown, University of Pennsylvania  (ktbrown@sas.upenn.edu)

Marcelina Martynek, University of Pennsylvania  (martynek@sas.upenn.edu)

Benjamin Glass, University of Pennsylvania  (benglass@sas.upenn.edu)