Abstract:The 1998 and 2016 thermal anomalies were among the 2 most severe global-scale anomalies in recent history, with broad-scale impacts on reef condition. In 2 Kenyan fully protected national park reef lagoons, the water flow, light, and temperature exposure severity of these 2 events was grossly similar at 7.3 cm s -1 , ~50 Einsteins m −2 d −1 and ~85 degree-days above summer baseline. Yet, despite similarities in the coral communities' metrics over this time, the bleaching responses were diminished considerably … Show more
“…Only two species of the fifteen most common (P. astreoides and S. intersepta) experienced a slight increase in total colony mortality in 2015; however, the uptick was \ 2.0% for both these species when all other species saw reductions in total colony mortality from 2014 to 2015. Although the idea that corals can be less impacted by a second bleaching event may seem counterintuitive, this has been documented before in the eastern tropical Pacific, the Great Barrier Reef, French Polynesia, SE Asia, the Maldives, and Kenya (Glynn et al 2001;Maynard et al 2008;Thompson and van Woesik 2009;Guest et al 2012;Pratchett et al 2013;McClanahan and Muthiga 2014;McClanahan 2017). Other studies have reported the more intuitive trend of compounded impacts from repeated thermal stress events (e.g., Neal et al 2016).…”
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 experienced 7.7 degree heating weeks (DHW) and as a result 38.0% of corals bleached and an additional 36.6% were pale or partially bleached. In situ temperatures in summer of 2015 were even warmer, with the site experiencing 9.5 DHW. Despite the increased thermal stress in 2015, only 12.1% of corals were bleached in 2015, which was 3.1 times less than 2014. Partial mortality dropped from 17.6% of surveyed corals to 4.3% between 2014 and 2015, and total colony mortality declined from 3.4 to 1.9% between years. Total colony mortality was low over both years of coral bleaching with 94.7% of colonies surviving from 2014 to 2016. The reduction in bleaching severity and coral mortality associated with a second stronger thermal anomaly provides evidence that the response of Caribbean coral communities to annual bleaching is not strictly temperature dose dependent and that acclimatization responses may be possible even with short recovery periods. Whether the results from Cheeca Rocks represent an aberration or a true resilience potential is the subject of ongoing research.
“…Only two species of the fifteen most common (P. astreoides and S. intersepta) experienced a slight increase in total colony mortality in 2015; however, the uptick was \ 2.0% for both these species when all other species saw reductions in total colony mortality from 2014 to 2015. Although the idea that corals can be less impacted by a second bleaching event may seem counterintuitive, this has been documented before in the eastern tropical Pacific, the Great Barrier Reef, French Polynesia, SE Asia, the Maldives, and Kenya (Glynn et al 2001;Maynard et al 2008;Thompson and van Woesik 2009;Guest et al 2012;Pratchett et al 2013;McClanahan and Muthiga 2014;McClanahan 2017). Other studies have reported the more intuitive trend of compounded impacts from repeated thermal stress events (e.g., Neal et al 2016).…”
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 experienced 7.7 degree heating weeks (DHW) and as a result 38.0% of corals bleached and an additional 36.6% were pale or partially bleached. In situ temperatures in summer of 2015 were even warmer, with the site experiencing 9.5 DHW. Despite the increased thermal stress in 2015, only 12.1% of corals were bleached in 2015, which was 3.1 times less than 2014. Partial mortality dropped from 17.6% of surveyed corals to 4.3% between 2014 and 2015, and total colony mortality declined from 3.4 to 1.9% between years. Total colony mortality was low over both years of coral bleaching with 94.7% of colonies surviving from 2014 to 2016. The reduction in bleaching severity and coral mortality associated with a second stronger thermal anomaly provides evidence that the response of Caribbean coral communities to annual bleaching is not strictly temperature dose dependent and that acclimatization responses may be possible even with short recovery periods. Whether the results from Cheeca Rocks represent an aberration or a true resilience potential is the subject of ongoing research.
“…Laboratory studies have shown that back-to-back bleaching can turn some coral species thought to be winners, or resistant to heat stress, into losers and vice versa (Grottoli et al, 2014). Multiple studies have shown that corals are often less impacted by a second bleaching event when events are separated by several or more years (Glynn, Maté, Baker, & Calderon, 2001;Guest et al, 2012;Maynard, Anthony, Marshall, & Masiri, 2008;McClanahan, 2017). Yet, other studies have observed the expected pattern of additive, negative impacts with multiple bleaching events (Neal et al, 2016;Riegl & Purkis, 2015).…”
Section: Benthic Cover After Bleaching Recoverymentioning
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.
“…3) 30 . This raises the question of whether coral holobionts can be trained or modified to increase their damage thresholds and become better able to survive thermal extremes 6,77 .Fig. 3Damage threshold hypothesis ( a ) during a thermal bleaching event comparing how a tolerant and a suscpetible holobiont may respond, and ( b ) a potential mechanism for immune memory through mulitple perturbations…”
Section: Coral Bleaching and Breaching The Damage Thresholdmentioning
Climate change is killing coral at an unprecedented rate. As immune systems promote homeostasis and survival of adverse conditions I propose we explore coral health in the context of holobiont immunity.
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