Group items tagged

The adaptation of tropical coral communities to the world's hottest sea, the Persian/Arabian Gulf (PAG), has recently been associated with ecological selection acting on a group of coral-associated algal symbionts, the Symbiodinium thermophilum group. Previous studies have shown that considerable genetic diversity exists within the group and that group members found within the PAG are significantly differentiated from those found externally, in the Gulf of Oman and wider waters. However, little is known about this genetic diversity. As an initial step towards understanding whether this diversity could represent niche adapted, selectable populations within the S. thermophilum group that may act as natural sources of stress tolerant associations to Indo-Pacific reefs, we investigate whether the diversity is structured between populations and where the location of the internal-external genetic partition lies. We use regions of the nuclear ribosomal DNA (ITS1-5.8S-ITS2) and chloroplastic psbA gene (non-coding region) from >100 S. thermophilum group-harbouring Porites spp. (P. lobata, P. lutea, and P. harrisoni) sampled across steep temperature and salinity gradients to conduct analyses of variance and create maximum parsimony networks to assess genetic structure and (dis)similarity within and between populations of S. thermophilum found within the PAG and externally in the Gulf of Oman. Our analyses resolve a sharp genetic boundary between Symbiodinium populations in the western Strait of Hormuz and identify significant genetic structure between populations with as little as 20 km between them demonstrating that differentiation between populations is likely due to factors other than limited connectivity. Further, we hypothesize that genotypes identified outside of the PAG in the Gulf of Oman existing in near-oceanic salinities, yet thermally challenging waters, putatively represent candidates for stress-tolerant symbionts that could act as natural seed populations of st

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.

Deep-reef coral hates the light, prefers the shade.