Contributed Session.
Lead Organizer: Katie Barott, University of Pennsylvania (kbarott@sas.upenn.edu)
Co-organizers:
Kelly Luis, NASA Water Resources (kelly.m.luis@jpl.nasa.gov)
Presentations
04:30 PM
CHANGES IN SEASONAL CALCIFICATION AND PHOTOSYNTHESIS RATES OF REEF-BUILDING CORALS FOLLOWING A LEGACY OF REPEATED HEAT STRESS (9401)
Primary Presenter: Katie Barott, University of Pennsylvania (kbarott@sas.upenn.edu)
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.
04:45 PM
Warm-adapted Red Sea reefs have globally distinct metabolic rates (9024)
Primary Presenter: Vincent Saderne, KAUST, King Abdullah University of Science and Technology (vincent.saderne@kaust.edu.sa)
Coral reefs are in global decline due to climate change, shifting from net heterotrophic to autotrophic systems, impacting carbon cycles and ecosystem resilience. The Red Sea, with some of the warmest waters globally (summer temperatures exceeding 30°C and reaching 38°C) has been proposed as a potential refuge for coral reefs against climate change. However, Red Sea reefs metabolic dynamics are understudied. Here, we measured day and night Net Ecosystem Calcification (NEC) and Net Ecosystem Production (NEP) on two Red Sea reefs using a semi-Lagrangian approach in fall, spring, and during the 2023-2024 summer marine heatwave (11-12°C degree heating weeks). The heatwave strongly altered metabolic rates, leading to a shift toward net heterotrophy and dissolution. Notably, Red Sea reefs exhibited high NEP relative to NEC compared to global averages, functioning as short-term CO2 sinks and providing insights into future reef performance amid ongoing global warming.
05:00 PM
Priming for Survival: Does temperature variability increase the physiological preparation of reef-building corals to a severe marine heatwave? (9492)
Primary Presenter: Marcelina Martynek, University of Pennsylvania (martynek@upenn.edu)
Coral reefs are facing alarming declines, with the most extreme marine heatwave in recorded history occurring across the southern Great Barrier Reef (GBR) this year. Encouragingly, there is evidence that exposure to high diel temperature variability can ‘prime’ corals to withstand heat stress by promoting rapid physiological acclimatization. Yet, the last heatwave to occur at this location saw three times greater coral mortality within thermally variable habitats, leaving many questions on whether life-long acclimatization to temperature variability can protect corals during extreme heatwaves. Here, we characterize host physiological performance and microbial community composition of the reef-building coral Pocillopora damicornis across six sites varying in diel temperature fluctuations (2.4–7.7°C day-1) and three timepoints: (i) pre- (Sept. 2022), (ii) during (May 2024), and (iii) post- heat stress (Sept. 2024). Pre-heatwave, P. damicornis from intermediate temperature variability demonstrated the greatest host biomass and symbiont densities, suggesting that there may be an optimal priming exposure to promote resilience. Analyses of host and symbiont genetics, tissue energetics, symbiont physiology, and microbiome patterns are ongoing, and we hypothesize that during and post-heatwave microbial communities will ‘shift’ from pre-heatwave communities. Ultimately, this research aims to clarify the complex relationships between coral microbiomes and host physiology to help guide strategies to safeguard these crucial ecosystems amid ongoing climate challenges.
05:15 PM
LONGITUDINAL STUDY OF STONY CORAL TISSUE LOSS DISEASE AND THE MICROBIOME (9279)
Primary Presenter: Jeanne Bloomberg, Woods Hole Oceanographic Institution / Massachusetts Institute of Technology (jeanne.bloomberg@whoi.edu)
Stony coral tissue loss disease (SCTLD) caused dramatic coral declines across the Caribbean and is likely caused by bacteria transmitted via seawater. Thus far, field-based research on SCTLD-affected microbiomes primarily compares healthy and diseased corals from single time points with minimal attention to the seawater microbes. This study is the first longitudinal study of corals contracting SCTLD. From Colpophyllia natans colonies in the U.S. Virgin Islands, tissue and near-coral seawater were sampled on naïve reefs (2020) through the emergence and extent of the SCTLD outbreak (2024). SCTLD prevalence surveys and colony fate tracking were paired with sequencing of the 16S rRNA gene of bacteria and archaea in coral tissue and near-coral seawater. We found that the microbiomes from coral tissue exhibited high beta diversity over time, both within and between colonies, suggesting dysbiosis or disrupted coral health before SCTLD exposure. In contrast, the seawater samples showed a consistent microbial composition, which was disturbed by SCTLD near diseased colonies, and disturbance was most pronounced when the disease was in its epidemic phase in the USVI (2020-2021). When SCTLD entered its endemic phase (2023–2024), the disease caused little disruption in the near-coral seawater of diseased corals. The uniformity of reef water microbes surrounding healthy corals, and the disruption during the SCTLD epidemic, suggests that corals are experiencing environmental stress during disease epidemics, which may enhance disease transmission and disease lethality.
05:30 PM
NITROGEN ACQUISITION AND TRANSLOCATION WITHIN THE SCLERACTINIAN CORAL DIPLORIA LABYRINTHIFORMIS (9466)
Primary Presenter: Moriah Kunes, Princeton University (mkunes@princeton.edu)
Corals are able to thrive in oligotrophic waters due to their relationship with endosymbiotic dinoflagellates (Symbiodiniaceae). The coral-algal partnership depends on a delicate nutrient balance between internal nitrogen (N) recycling and N availability. Previous studies suggest that the host is the main N source for the algae; keeping symbionts N limited controls symbiont density, ensuring their excess photosynthate is translocated to the host. With reefs experiencing increasing nutrient pollution, it is essential to understand how the coral holobiont maintains a nutrient balance. Here under both in situ and nitrate (NO3-) enriched reef conditions, we explored the role of nutritional mode (autotrophy vs. heterotrophy) in acquiring N and the fate of N in the holobiont. Using outdoor incubations, Diploria labyrinthiformis was exposed for 24 h to four experimental treatments using 15N tracer to label either zooplankton or NO3- (the form of inorganic N available to symbiont but not host). NO3- was taken up by the symbionts but was not translocated to the host. The coral fed on zooplankton and some zooplankton-N was quickly (< 3 h) transferred to the symbionts (likely as ammonium, NH4+) in both low and high NO3- conditions. Thus, ambient NO3- did not affect the symbionts’ preference for recycled nitrogen waste (NH4+) from the host. By tracing the fate of N when both nutritional modes were available, we found that N can be taken up both ways but is conserved within the symbionts if acquired through autotrophy and translocated from host to symbionts if acquired through feeding.
05:45 PM
Clearing a path to resilience: removal of dead coral skeletons mitigates downstream impacts of marine heatwaves on coral reefs (9419)
Primary Presenter: Kai Kopecky, University of Colorado Boulder (kai.kopecky@colorado.edu)
Ecological disturbance regimes are shifting and leaving behind novel legacies, like the remnant structures of dead foundation species, which have poorly known impacts on ecosystem resilience. On coral reefs, the primary source of mass coral mortality has historically been powerful tropical storms that kill corals and remove their skeletons from the reef. More recently, there has been a rise in the prevalence of other disturbances, like marine heatwaves that cause coral bleaching or outbreaks of coral predators, both of which kill corals but leave their structurally complex skeletons intact. We explored how the physical environment created by standing dead coral skeletons influences the outcomes of spatial competition between corals and macroalgae, relative to when dead skeletons are removed. Following a marine heatwave, we removed dead skeletons from reef patches then used underwater photogrammetry and AI-powered image analysis to quantify trajectories of coral and macroalgae, which constitute alternative community states in this system. We found several lines of evidence indicating that dead skeletons act as an alternative substrate type that facilitates the buildup of macroalgae and drives the continued loss of live coral after disturbance. More encouragingly, however, we also found that removing dead skeletons can mitigate these adverse effects. Our findings identify a promising avenue to manage for coral reef resilience and reveal how changing disturbance regimes can create novel physical environments that sway the outcomes of spatial competition.
CS06 - Coral Reef Ecosystems
Description
Time: 4:30 PM
Date: 31/3/2025
Room: W207AB