Red Sea Atlas of Coral-Associated Bacteria Highlights Common Microbiome Members and Their Distribution across Environmental Gradients-A Systematic Review

Abstract

The Red Sea is a suitable model for studying coral reefs under climate change due to its strong environmental gradient that provides a window into future global warming scenarios. For instance, corals in the southern Red Sea thrive at temperatures predicted to occur at the end of the century in other biogeographic regions. Corals in the Red Sea thrive under contrasting thermal and environmental regimes along their latitudinal gradient. Because microbial communities associated with corals contribute to host physiology, we conducted a systematic review of the known diversity of Red Sea coral-associated bacteria, considering geographic location and host species. Our assessment comprises 54 studies of 67 coral host species employing cultivation-dependent and cultivation-independent techniques. Most studies have been conducted in the central and northern Red Sea, while the southern and western regions remain largely unexplored. Our data also show that, despite the high diversity of corals in the Red Sea, the most studied corals were Pocillopora verrucosa, Dipsastraea spp., Pleuractis granulosa, and Stylophora pistillata. Microbial diversity was dominated by bacteria from the class Gammaproteobacteria, while the most frequently occurring bacterial families included Rhodobacteraceae and Vibrionaceae. We also identified bacterial families exclusively associated with each of the studied coral orders: Scleractinia (n = 125), Alcyonacea (n = 7), and Capitata (n = 2). This review encompasses 20 years of research in the Red Sea, providing a baseline compendium for coral-associated bacterial diversity.

Keywords: Red Sea; bacterial diversity; coral reefs; coral-associated bacteria; microbial ecology; microbiology.

Figure 1

Systematic review of published studies investigating bacterial communities associated with corals along the Red Sea using a literature survey in the PubMed and Web of Science databases. (A) Map showing the spatial distribution and density of sampling sites of coral-associated bacteria along the latitudinal gradient of the Red Sea; (B) Bar graph indicating the number of published papers (n = 54) of studies in the Red Sea over the past two decades (2000—February 2021); (C) Bar graph representing coral groups (hard vs. soft), sampling depths (photic 0–50 m vs. aphotic zone 300–1000 m), study techniques (culture-dependent techniques vs. culture-independent techniques), and coral health state (healthy vs. unhealthy) used in the retrieved publications; (D) Flowchart following PRISMA guidelines, summarizing the retrieved publications, including the number of studied coral taxa and techniques used for the bacterial diversity Atlas.

Figure 2

Coral-associated bacteria across all coral species and studies, grouped at four different taxonomic levels. (A) Phylum; (B) Class; (C) Order and (D) Family. For each graph, the Y-axis represents the percentage of occurrence. Groups with the lowest occurrence in the different taxonomic levels were grouped into “Others”. Unclassified groups and “Others” for order and family levels are available in Supplementary Material S2. Colors used for class-, order- and family-level graphs represent members of the same phylum.

Figure 3

(A) Bacterial diversity (by number) at the family level for 35 coral taxa according to data retrieved from the selected publications in this study. Seven coral species showed a higher number of bacterial families (n > 130). (B) Bacterial families reported in 10 or more coral taxa. (C) Venn diagram showing the number of common and exclusively reported bacterial families among Red Sea regions.

Figure 4

The Red Sea coral-associated bacterial Atlas: Coral-associated bacteria across Red Sea coral species. The reported families are shown. Due to space constraints, coral hosts are not presented by taxonomic classification, but rather by the overall abundance of associated bacterial families. The number of studies included for the Atlas, per coral species (n), and the corresponding location of the study sites in the Red Sea are indicated in the map inset close to the image in vivo.

Figure 4

The Red Sea coral-associated bacterial Atlas: Coral-associated bacteria across Red Sea coral species. The reported families are shown. Due to space constraints, coral hosts are not presented by taxonomic classification, but rather by the overall abundance of associated bacterial families. The number of studies included for the Atlas, per coral species (n), and the corresponding location of the study sites in the Red Sea are indicated in the map inset close to the image in vivo.

Figure 4

The Red Sea coral-associated bacterial Atlas: Coral-associated bacteria across Red Sea coral species. The reported families are shown. Due to space constraints, coral hosts are not presented by taxonomic classification, but rather by the overall abundance of associated bacterial families. The number of studies included for the Atlas, per coral species (n), and the corresponding location of the study sites in the Red Sea are indicated in the map inset close to the image in vivo.

Figure 4

The Red Sea coral-associated bacterial Atlas: Coral-associated bacteria across Red Sea coral species. The reported families are shown. Due to space constraints, coral hosts are not presented by taxonomic classification, but rather by the overall abundance of associated bacterial families. The number of studies included for the Atlas, per coral species (n), and the corresponding location of the study sites in the Red Sea are indicated in the map inset close to the image in vivo.

Figure 4

The Red Sea coral-associated bacterial Atlas: Coral-associated bacteria across Red Sea coral species. The reported families are shown. Due to space constraints, coral hosts are not presented by taxonomic classification, but rather by the overall abundance of associated bacterial families. The number of studies included for the Atlas, per coral species (n), and the corresponding location of the study sites in the Red Sea are indicated in the map inset close to the image in vivo.

Figure 5

Bacterial families exclusively identified according to the coral order. (A) Sankey diagram showing the families exclusively associated with hard corals and hydrocorals (Scleractinia and Capitata) and soft corals (Alcyonacea). The number each bacterial family was reported across studies is shown. (B) Venn diagram showing the number of common and exclusively reported bacterial families among coral orders.

Figure 6

Coral-associated bacteria based on the examined culture-dependent studies. (A) Number of reported bacterial families associated with different coral species. (B) Frequency of bacterial diversity at the family level. Bacterial families are color-coded per phylum following Figure 2. Families with a lower frequency were grouped under “Others”.