Abstract:Annual coral bleaching events, which are predicted to occur as early as the next decade in the Florida Keys, are expected to cause catastrophic coral mortality. Despite this, there is little field data on how Caribbean coral communities respond to annual thermal stress events. At Cheeca Rocks, an inshore patch reef near Islamorada, FL, the condition of 4234 coral colonies was followed over 2 yr of subsequent bleaching in 2014 and 2015, the two hottest summers on record for the Florida Keys. In 2014, this site … Show more
“…The average tissue loss of 21% indicates that stress was a factor, but whether this was reflective of what was happening at the time to wild colonies at the respective sites is unknown. Orbicella faveolata is remarkably resistant to complete mortality (Edmunds ), as recently demonstrated in the Florida Keys during repetitive bleaching events in 2014 and 2015 (Gintert et al ); however, percent coverage of Orbicella spp. across the Florida reef tract has declined significantly since 1998, most likely because of partial mortality (Toth et al ).…”
The decline in living coral since the 1970s has conspicuously slowed reef construction on a global scale, but the related process of reef erosion is less visible and not often quantified. Here, we present new data on the constructional and deconstructional sides of the carbonate‐budget equation in the Florida Keys, U.S.A. We documented Orbicella spp. calcification rates at four offshore reefs and quantified decadal‐scale rates of Orbicella‐reef erosion at a mid‐shore patch reef. Using Orbicella coral heads fitted with permanent markers in 1998, we measured reef‐elevation loss at 28 stations over 17.3 yr to estimate a mean erosion rate of −5.5 (± 3.2, SD) mm yr−1. This loss equates to an erosion rate of −8.2 (± 4.8, SD) kg m−2 yr−1 on dead Orbicella colonies, or −6.6 kg m−2 yr−1 when adjusted reef‐wide. Calculating net carbonate production using a census‐based approach on the same patch reef in 2017, we estimated a reef‐wide bioerosion rate of −1.9 (± 2.0, SD) kg m−2 yr−1, and a net carbonate production rate of 0.5 (± 0.3, SD) kg m−2 yr−1. Substituting the erosion rate we estimated with the markers would suggest that net carbonate production at this patch reef was lower and negative, −4.2 kg m−2 yr−1. This divergence could be a function of high erosion rates measured on the tops of Orbicella colonies, which may be preferentially targeted by parrotfish. Nonetheless, our study suggests the need for new field data to improve estimates of reef‐structure persistence as coral reefs continue to degrade.
“…The average tissue loss of 21% indicates that stress was a factor, but whether this was reflective of what was happening at the time to wild colonies at the respective sites is unknown. Orbicella faveolata is remarkably resistant to complete mortality (Edmunds ), as recently demonstrated in the Florida Keys during repetitive bleaching events in 2014 and 2015 (Gintert et al ); however, percent coverage of Orbicella spp. across the Florida reef tract has declined significantly since 1998, most likely because of partial mortality (Toth et al ).…”
The decline in living coral since the 1970s has conspicuously slowed reef construction on a global scale, but the related process of reef erosion is less visible and not often quantified. Here, we present new data on the constructional and deconstructional sides of the carbonate‐budget equation in the Florida Keys, U.S.A. We documented Orbicella spp. calcification rates at four offshore reefs and quantified decadal‐scale rates of Orbicella‐reef erosion at a mid‐shore patch reef. Using Orbicella coral heads fitted with permanent markers in 1998, we measured reef‐elevation loss at 28 stations over 17.3 yr to estimate a mean erosion rate of −5.5 (± 3.2, SD) mm yr−1. This loss equates to an erosion rate of −8.2 (± 4.8, SD) kg m−2 yr−1 on dead Orbicella colonies, or −6.6 kg m−2 yr−1 when adjusted reef‐wide. Calculating net carbonate production using a census‐based approach on the same patch reef in 2017, we estimated a reef‐wide bioerosion rate of −1.9 (± 2.0, SD) kg m−2 yr−1, and a net carbonate production rate of 0.5 (± 0.3, SD) kg m−2 yr−1. Substituting the erosion rate we estimated with the markers would suggest that net carbonate production at this patch reef was lower and negative, −4.2 kg m−2 yr−1. This divergence could be a function of high erosion rates measured on the tops of Orbicella colonies, which may be preferentially targeted by parrotfish. Nonetheless, our study suggests the need for new field data to improve estimates of reef‐structure persistence as coral reefs continue to degrade.
“…However, we argue that it is more likely that shuffling drove this change in region‐wide symbiont dominance given that O. faveolata is well documented to host multiple symbiont genera simultaneously as well as readily shuffle to dominance by D. trenchii during and after bleaching (Kemp et al., ). Long‐term monitoring at UKI1, a reef where O. faveolata is the most abundant coral , revealed that only 4 of 552 tracked colonies (<1%) died during the 2014–2015 bleaching (Gintert et al., ).…”
Section: Discussionmentioning
confidence: 99%
“…Therefore, the response to bleaching in O. faveolata in 2014 and 2015 appears to be different than the prior Keys‐wide mass bleaching event in 2005. This difference may be because the bleaching in 2005 was less severe than 2014 and 2015, owing to less heat stress in 2005 (see Gintert et al., ).…”
Identifying which factors lead to coral bleaching resistance is a priority given the global decline of coral reefs with ocean warming. During the second year of back‐to‐back bleaching events in the Florida Keys in 2014 and 2015, we characterized key environmental and biological factors associated with bleaching resilience in the threatened reef‐building coral Orbicella faveolata. Ten reefs (five inshore, five offshore, 179 corals total) were sampled during bleaching (September 2015) and recovery (May 2016). Corals were genotyped with 2bRAD and profiled for algal symbiont abundance and type. O. faveolata at the inshore sites, despite higher temperatures, demonstrated significantly higher bleaching resistance and better recovery compared to offshore. The thermotolerant Durusdinium trenchii (formerly Symbiondinium trenchii) was the dominant endosymbiont type region‐wide during initial (78.0% of corals sampled) and final (77.2%) sampling; >90% of the nonbleached corals were dominated by D. trenchii. 2bRAD host genotyping found no genetic structure among reefs, but inshore sites showed a high level of clonality. While none of the measured environmental parameters were correlated with bleaching, 71% of variation in bleaching resistance and 73% of variation in the proportion of D. trenchii was attributable to differences between genets, highlighting the leading role of genetics in shaping natural bleaching patterns. Notably, D. trenchii was rarely dominant in O. faveolata from the Florida Keys in previous studies, even during bleaching. The region‐wide high abundance of D. trenchii was likely driven by repeated bleaching associated with the two warmest years on record for the Florida Keys (2014 and 2015). On inshore reefs in the Upper Florida Keys, O. faveolata was most abundant, had the highest bleaching resistance, and contained the most corals dominated by D. trenchii, illustrating a causal link between heat tolerance and ecosystem resilience with global change.
“…Another study from Florida demonstrated lower rates of bleaching and mortality by observing more than 4,000 coral colonies of multiple species in the second of successive mass bleaching events (Gintert et al, ). This study suggest broad community level acclimatization because the second bleaching event resulted in moderate impacts despite accrued additional degree heating weeks, which typically tracks closely with bleaching severity (Hughes, Kerry, et al, ).…”
Section: Ecological Signatures Of Acclimatization In Coralsmentioning
Coral reefs are under extreme threat due to a number of stressors, but temperature increases due to changing climate are the most severe. Rising ocean temperatures coupled with local extremes lead to extensive bleaching, where the coral‐algal symbiosis breaks down and corals may die, compromising the structure and function of reefs. Although the symbiotic nature of the coral colony has historically been a focus of research on coral resilience, the host itself is a foundational component in the response to thermal stress. Fixed effects in the coral host set trait baselines through evolutionary processes, acting on many loci of small effect to create mosaics of thermal tolerance across latitudes and individual coral reefs. These genomic differences can be strongly heritable, producing wide variation among clones of different genotypes or families of a specific larval cross. Phenotypic plasticity is overlaid on these baselines and a growing body of knowledge demonstrates the potential for acclimatization of reef‐building corals through a variety of mechanisms that promote resilience and stress tolerance. The long‐term persistence of coral reefs will require many of these mechanisms to adjust to warmer temperatures within a generation, bridging the gap to reproductive events that allow recombination of standing diversity and adaptive change. Business‐as‐usual climate scenarios will probably lead to the loss of some coral populations or species in the future, so the interaction between intragenerational effects and evolutionary pressure is critical for the survival of reefs.
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