Abstract
BackgroundThe capacity of reef-building corals to tolerate (or adapt to) heat stress is a key factor determining their resilience to future climate change. Changes in coral microbiome composition (particularly for microalgal endosymbionts and bacteria) is a potential mechanism that may assist corals to thrive in warm waters. The northern Red Sea experiences extreme temperatures anomalies, yet corals in this area rarely bleach suggesting possible refugia to climate change. However, the coral microbiome composition, and how it relates to the capacity to thrive in warm waters in this region, is entirely unknown.ResultsWe investigated microbiomes for six coral species (Porites nodifera, Favia favus, Pocillopora damicornis, Seriatopora hystrix, Xenia umbellata, and Sarcophyton trocheliophorum) from five sites in the northern Red Sea spanning 4° of latitude and summer mean temperature ranges from 26.6 °C to 29.3 °C. A total of 19 distinct dinoflagellate endosymbionts were identified as belonging to three genera in the family Symbiodiniaceae (Symbiodinium, Cladocopium, and Durusdinium). Of these, 86% belonged to the genus Cladocopium, with notably five novel types (19%). The endosymbiont community showed a high degree of host-specificity despite the latitudinal gradient. In contrast, the diversity and composition of bacterial communities of the surface mucus layer (SML)—a compartment particularly sensitive to environmental change—varied significantly between sites, however for any given coral was species-specific.ConclusionThe conserved endosymbiotic community suggests high physiological plasticity to support holobiont productivity across the different latitudinal regimes. Further, the presence of five novel algal endosymbionts suggests selection of certain genotypes (or genetic adaptation) within the semi-isolated Red Sea. In contrast, the dynamic composition of bacteria associated with the SML across sites may contribute to holobiont function and broaden the ecological niche. In doing so, SML bacterial communities may aid holobiont local acclimatization (or adaptation) by readily responding to changes in the host environment. Our study provides novel insight about the selective and endemic nature of coral microbiomes along the northern Red Sea refugia.
Highlights
Coral reefs have dramatically declined during the last two decades through the mortality of reef-building species driven by frequent and intense heatwaves [1, 2]
Symbiodiniaceae community structure Samples were collected from six coral species to represent taxonomic and functional diversity, at two depths along five sites (n = 163) with different thermal regimes in the northern Red Sea (Fig. 1, see [4])
We assessed the composition of coral dinoflagellate endosymbionts and the surface mucus layer (SML) bacterial community for six abundant coral species inhabiting the northern Red Sea, an area recently proposed as a refuge for corals against thermal stress events [4, 45]
Summary
Coral reefs have dramatically declined during the last two decades through the mortality of reef-building species driven by frequent and intense heatwaves [1, 2]. Corals can persist in relatively extreme habitats such as shallow pools [5], reef flats [6], and mangroves [7, 8], or marginally “hot” reef systems such as those within parts of the Persian-Arabian Gulf [9] and the Red Sea [4]. The capacity of reef-building corals to tolerate (or adapt to) heat stress is a key factor determining their resilience to future climate change. Changes in coral microbiome composition ( for microalgal endosymbionts and bacteria) is a potential mechanism that may assist corals to thrive in warm waters. The coral microbiome composition, and how it relates to the capacity to thrive in warm waters in this region, is entirely unknown
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