Abstract
As seawater temperature rises, repeated thermal bleaching events have negatively affected the reefs of the Andaman Sea for over decades. Studies on the coral-associated microbial diversity of prokaryotes and microbial eukaryotes (microbiome) in healthy and bleached corals are important to better understand the coral holobionts that involved augmented resistance to stresses, and this information remains limited in the Andaman Sea of Thailand. The present study thereby described the microbiomes of healthy (unbleached) and bleached colonies of four prevalent corals, Acropora humilis, Platygyra sp., Pocillopora damicornis, and Porites lutea, along with the surrounding seawater and sediments, that were collected during a 2016 thermal bleaching event, using 16S and 18S rRNA genes next-generation sequencing (NGS). Both prokaryotic and eukaryotic microbes showed isolated community profiles among sample types (corals, sediment, and seawater) [analysis of similarities (ANOSIM): p = 0.038 for prokaryotes, p < 0.001 for microbial eukaryotes] and among coral genera (ANOSIM: p < 0.001 for prokaryotes and microbial eukaryotes). In bleached state corals, we found differences in microbial compositions from the healthy state corals. Prevalent differences shared among bleached coral genera (shared in at least three coral genera) included a loss of reported coral-beneficial microbes, such as Pseudomonadales, Alteromonadales, and Symbiodinium; meanwhile an increase of putative coral-pathogenic Malassezia and Aspergillus. This difference could affect carbon and nitrogen availability for coral growth, reflective of a healthy or bleached state. Our findings in part supported previously microbial dysbiosis knowledge of thermal bleaching coral microbiomes around South East Asia marine geography, and together ongoing efforts are to support the understanding and management of microbial diversity to reduce the negative impacts to corals in massive thermal bleaching events.
Highlights
Coral bleaching is defined as a breakdown of coral-algae symbiosis, when the corals are stressed by a variety of factors, in which the increased atmosphere temperature is the major triggering cause, and the endosymbiotic algae expel (Hoegh-Guldberg and Smith, 1989; Bruno et al, 2001; Eakin et al, 2010)
Venn diagrams showed that bleached corals had relatively fewer number of genus operational taxonomic units (OTUs) than healthy corals in approximately half the number (Figure 1E; Pollock et al, 2019); this lower alpha diversity was not held true to every coral species, in part highlighting the report that the alpha diversity of the stressed corals, regardless of the stressor, could carry the more alpha diversity (McDevitt-Irwin et al, 2017), and these differences might be associated with coral species and their associated microbiome (Kusdianto et al, 2021)
Following our first report of both prokaryotic and microbial eukaryotic profiles associated with coral genera and their sediment and seawater surroundings in the upper Gulf of Thailand (Kusdianto et al, 2021), the present study continued firstly characterizing the microbiome compositions of four coral genera exhibited in healthy and bleached corals collected from the Andaman Sea of Thailand during the 2016 thermal bleaching event to better understand the healthy and bleached coral-associated microbiome and in the slight different Thailand marine geography
Summary
Coral bleaching is defined as a breakdown of coral-algae symbiosis, when the corals are stressed by a variety of factors, in which the increased atmosphere temperature ( seawater temperature) is the major triggering cause, and the endosymbiotic algae (in particular photosynthetic dinoflagellate Symbiodinium) expel (Hoegh-Guldberg and Smith, 1989; Bruno et al, 2001; Eakin et al, 2010). Thermal bleaching events are considered as the most problematic coral situation worldwide, including in the Andaman Sea coast of Thailand where the first widespread thermal bleaching event was recorded in 1991 and subsequently recurred in 1995, 1998, 2003, 2010 (severe event), and 2016, respectively (Phongsuwan and Chansang, 2012). The 2010 bleaching event caused 44.2–99.0% coral mortality (Brown et al, 1996; Phongsuwan and Chansang, 2012). In the 2016 bleaching event, approximately 50% of the corals were affected; this was considered moderate bleaching-induced mortality (Pootakham et al, 2018). The mortality of corals affects the nursing habitats of diverse marine fish and invertebrates (Boilard et al, 2020)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
