Marked annual coral bleaching resilience of an inshore patch reef in the Florida Keys: A nugget of hope, aberrance, or last man standing?

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 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.

Improving estimates of coral reef construction and erosion with in situ measurements

“…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 ).…”

Role of host genetics and heat‐tolerant algal symbionts in sustaining populations of the endangered coral Orbicella faveolata in the Florida Keys with ocean warming

“…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., ).…”

“…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., ).…”

Resilience in reef‐building corals: The ecological and evolutionary importance of the host response to thermal stress

“…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, ).…”