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Increasingly frequent marine heatwaves are devastating coral reefs. Corals that survive these extreme events must rapidly recover if they are to withstand subsequent events, and long-term survival in the face of rising ocean temperatures may hinge on recovery capacity and acclimatory gains in heat tolerance over an individual’s lifespan. To better understand coral recovery trajectories in the face of successive marine heatwaves, we monitored the responses of bleaching-susceptible and bleaching-resistant individuals of two dominant coral species in Hawai’i,Montipora capitataandPorites compressa, over a decade that included three marine heatwaves. Bleaching-susceptible colonies ofP. compressaexhibited beneficial acclimatization to heat stress (i.e., less bleaching) following repeat heatwaves, becoming indistinguishable from bleaching-resistant conspecifics during the third heatwave. In contrast, bleaching-susceptibleM. capitatarepeatedly bleached during all successive heatwaves and exhibited seasonal bleaching and substantial mortality for up to 3 y following the third heatwave. Encouragingly, bleaching-resistant individuals of both species remained pigmented across the entire time series; however, pigmentation did not necessarily indicate physiological resilience. Specifically,M. capitatadisplayed incremental yet only partial recovery of symbiont density and tissue biomass across both bleaching phenotypes up to 35 mo following the third heatwave as well as considerable partial mortality. Conversely,P. compressaappeared to recover across most physiological metrics within 2 y and experienced little to no mortality. Ultimately, these results indicate that even some visually robust, bleaching-resistant corals can carry the cost of recurring heatwaves over multiple years, leading to divergent recovery trajectories that may erode coral reef resilience in the Anthropocene.
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Evidence of rare occurrences of the Phoenix effect in the Hawaiian corals Porites compressa and Montipora capitata following mortality induced by a marine heatwave
Coral bleaching is a common stress response to extreme temperatures experienced during marine heatwaves. Bleached corals are left vulnerable without the nutritional support of their algal symbionts, and can often suffer partial or complete mortality. Bleaching-induced mortality is often accompanied by colonization of turf algae over the dead coral skeleton, which can be difficult for corals to regrow over. The Phoenix effect is a phenomenon of rapid recovery of live coral tissue following mortality, which is hypothesized to occurviathe regrowth of tissue from deep within the coral skeleton that expands over the top of dead portions. Here, we found that the Hawaiian coralsPorites compressaandMontipora capitatacan display rapid tissue recovery suggestive of the Phoenix effect. During a marine heatwave that occurred in 2015 in Kāne’ohe Bay, Hawai’i, USA, 237 individuals (including bleached and non-bleached phenotypes) were identified and monitored for mortality and recovery over the next 2–7 years. Nearly 16% ofP. compressaindividuals and 34% ofM. capitataexhibited substantial partial mortality, and approximately half of these affected individuals of each species had bleached during the heatwave. Partial mortality following the 2015 heatwave was followed by turf algae colonization over the exposed skeleton. Of the colonies with substantial mortality, six colonies (10% of affected individuals; fiveP. compressaand oneM. capitata) subsequently recovered to over 90% live coral tissue within 2 years (2017), with an additional three colonies (twoP. compressaand oneM. capitata) recovering within 4 years of the 2015 marine heatwave (2019). We qualify colonies with rapid tissue recovery as those that meet two criteria: (1) substantial partial mortality (≥40%) in the first 12 months following the initial 2015 marine heatwave, and (2) recovery of any amount of live tissue at anytime before 2022. Interestingly, only colonies that had bleached in 2015 exhibited rapid tissue recovery. A consecutive, yet less severe marine heatwave occurred in 2019, and none of the previously recovered colonies observed experienced significant tissue loss, suggesting these individuals remained resilient amidst a secondary heat stress exposure. This phenomenon is an example of remarkable recovery and resilience that may be informative for further study of mechanisms of coral tissue regeneration in two important reef-building coral species.
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- Award ID(s):
- 2237658
- PAR ID:
- 10677945
- Publisher / Repository:
- PeerJ
- Date Published:
- Journal Name:
- PeerJ
- Volume:
- 13
- ISSN:
- 2167-8359
- Page Range / eLocation ID:
- e19225
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.7717/peerj.19225
