Coral reefs are in global decline due to ocean warming and ocean acidification. While
these stressors are commonly studied in climate change predictions, salinity, although
being an important environmental factor, is not well understood. The response of the
coral holobiont (the association of the coral host, its algal endosymbiont and a suit of
other microbes) to changes in salinity and the contribution of each holobiont
compartment underlying the necessary osmoadaptation remain especially elusive.
Interestingly, we find some of the most thermotolerant corals in some of the most saline
seas, e.g. the Red Sea and the Persian Arabian Gulf. This observation sparked the
hypothesis of a link between osmoadaptation and coral thermotolerance. Here, we set out
to elucidate the putative effects of high salinity on conveying thermotolerance and
thereby a possible link to bleaching in the context of the coral holobiont. For this, we
conducted a series of heat stress experiments at different salinities in the coral model
Aiptasia and subsequently validated our findings in corals from the central Red Sea. We
confirm a role of osmoadaptation in increased thermotolerance and reduced bleaching in
Aiptasia and Red Sea corals. This salinity-conveyed thermotolerance was characterized
by a reduction in algal endosymbiont loss, photosystem damage and leakage of damaging
reactive oxygen species (ROS) in high salinity. Further analysis of the osmoadaptation
response using targeted GC-MS uncovered high levels of the sugar floridoside at high
salinity only in holobionts that show the salinity-conveyed thermotolerance. The increase
of floridoside, an osmolyte capable of scavenging ROS, and the concurrent reduction of
ROS argues for a mechanistic link of increased thermotolerance and reduced bleaching in
high salinities. In addition, the restructuring of the microbiome at high salinity that
aligned with the difference in thermotolerance in Aiptasia may be indicative of a
microbial contribution towards a more beneficial holobiont composition. Hence,
emphasizing the potential cumulative contribution of each holobiont compartment during
stress-resilience, as well as highlighting the overall role of osmoadaptation in the
thermotolerance of corals.
| Identifer | oai:union.ndltd.org:kaust.edu.sa/oai:repository.kaust.edu.sa:10754/629997 |
| Date | 11 1900 |
| Creators | Gegner, Hagen |
| Contributors | Voolstra, Christian R., Biological and Environmental Sciences and Engineering (BESE) Division, Aranda, Manuel, Tester, Mark A., Schmitt-Kopplin, Philippe |
| Source Sets | King Abdullah University of Science and Technology |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | 2019-11-22, At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2019-11-22. |
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