High diversity of benthic cyanobacterial mats on coral reefs of Koh Tao, Gulf of Thailand

Abstract

Benthic cyanobacterial mats are increasingly reported to cover major coral reef areas. Although suggestions have been made that cyanobacterial mats impair coral reef health in multiple ways, information is lacking regarding the distribution, morphotypical variation and bacterial species composition of these microbial mats. As such, this study aimed to (1) Reveal the bacterial community diversity and composition of different mat morphotypes, (2) Identify the most abundant community members and closely related organisms, (3) Assess to what extent, morphotype, colonized substrate (coral or abiotic substrate), depth, and site were significant predictors of bacterial composition. Data were collected on reefs surrounding the island of Koh Tao (Gulf of Thailand). A total of 201 mats from 16 different locations around the island were classified into eight distinct morphotypes. Of these, the bacterial communities of 44 mats, representing colour groups from multiple sites, were characterized using 16S rRNA gene high-throughput sequencing. Our data revealed that Proteobacteria, Cyanobacteria, Bacteriodetes and Planctomycetes were the four most abundant phyla and occurred in all samples. Abundant cyanobacterial zero-radius operational taxonomic units (ZOTUs) were closely related to prokaryotic sequences found in previous studies of coastal mats (98–100%) and were assigned to genera in the order Oscillatoriales, e.g. Hormoscilla, Okeania, and Oscillatoria. Abundant proteobacterial ZOTUs were assigned to orders in the classes Alpha- and Gammaproteobacteria, e.g. Rhodobacterales, Rhizobiales and Alteromonadales. Abundant Bacteriodetes ZOTUs were mainly assigned to the class Bacteroidia and order Cytophagales. Our results showed that mats consist of a diverse and variable bacterial consortium, with mat colour (morphotype), substrate type and geographic location only explaining a small part of the total variation in composition.

Predation, community asynchrony, and metacommunity stability in cyanobacterial mats

“…The influence of both local and global stressors is driving near-ubiquitous increases in the proportional cover of conspicuous benthic cyanobacterial mats on coral reefs worldwide (reviewed in Ford et al 2018), including increasing the relative cover of spatially discrete, horizontally-spreading mat carpets (de Bakker et al 2017) and vertically tufting cyanobacteria (Ford et al 2021), as well as increasing the duration and magnitude of extensive (i.e., kilometer-scale) benthic bloom events (Hewson et al 2001, Paul et al 2005). Similar to microbial mats found in other systems (Bolhuis et al 2014), cyanobacterial mats found on coral reefs are complex and strongly cooperative microbial consortia (Cissell and McCoy 2021, Stuij et al 2022). Coral reef cyanobacterial mats, while structurally built by phototrophic cyanobacterial taxa, also contain a taxonomically and functionally diverse suite of microbial eukaryotes, heterotrophic bacteria, and viruses (Cissell and McCoy 2021, Stuij et al 2022).…”

“…Similar to microbial mats found in other systems (Bolhuis et al 2014), cyanobacterial mats found on coral reefs are complex and strongly cooperative microbial consortia (Cissell and McCoy 2021, Stuij et al 2022). Coral reef cyanobacterial mats, while structurally built by phototrophic cyanobacterial taxa, also contain a taxonomically and functionally diverse suite of microbial eukaryotes, heterotrophic bacteria, and viruses (Cissell and McCoy 2021, Stuij et al 2022). Expanding cover of cyanobacterial mats generates complex feedback loops with other major causes of reef degradation, and may exacerbate the velocity and magnitude of existing trajectories of reef decline (Ethan C. Cissell and McCoy 2022).…”

Viral association with cyanobacterial mat community mortality

“…Benthic cyanobacterial mats (BCMs) are becoming increasingly dominant members of coral reef communities worldwide due to the influence of both local and global stressors (Cissell & McCoy, 2022a; de Bakker et al, 2017; Ford et al, 2018). We define coral reef BCMs as a functional grouping that broadly encompasses taxonomically and functionally rich, conspicuous benthic consortia primarily comprised of prokaryotic members of the phyla Cyanobacteria (dominating the construction and maintenance of mat structural complexity), Proteobacteria, and Bacteroidetes (Cissell & McCoy, 2021; Stuij et al, 2022). The proliferation of BCMs on coral reefs is both a product of and itself exacerbates reef degradation, with feedback among BCM cover and major drivers of reef decline such as shifting reef carbon chemistry and coral disease transmission (Brocke, Polerecky, et al, 2015; Cissell et al, 2022).…”

Divide and conquer: Spatial and temporal resource partitioning structures benthic cyanobacterial mats

“…Benthic cyanobacterial mats (BCMs) are complex, layered structures with high structural, spatial, and temporal heterogeneity (Figure 1). These BCMs consist of a consortium of bacteria, archaea, eukarya, viruses, and more, with the Cyanobacteria, Proteobacteria, and Bacteroidetes often dominating these communities (e.g., Cissell & McCoy, 2021;Stuij et al, 2023). Benthic cyanobacterial mats are vertically stratified in temperate marine (e.g., Carreira et al, 2015), hypersaline (e.g., Dillon et al, 2009), and freshwater systems (e.g., Borovec et al, 2010;Velázquez et al, 2017), while those in tropical marine systems have more distinct horizontal spatial differences (e.g., Cissell & McCoy, 2021).…”