DOI 10.1186/s40168-023-01711-x Background
Climate change has accelerated the occurrence and severity of heatwaves in the Mediterranean Sea and poses a significant threat to the octocoral species that form the foundation of marine animal forests (MAFs). As coral health intricately relies on the symbiotic relationships established between corals and microbial communities, our goal was to gain a deeper understanding of the role of bacteria in the observed tissue loss of key octocoral species following the unprecedented heatwaves in 2022.
Results
Using amplicon sequencing and taxon-specific qPCR analyses, we unexpectedly found that the absolute abundance of the major bacterial symbionts, Spirochaetaceae (C. rubrum) and Endozoicomonas (P. clavata), remained, in most cases, unchanged between colonies with 0% and 90% tissue loss. These results suggest that the impairment of coral health was not due to the loss of the main bacterial symbionts. However, we observed a significant increase in the total abundance of bacterial opportunists, including putative pathogens such as Vibrio, which was not evident when only their relative abundance was considered. In addition, there was no clear relation between bacterial symbiont loss and the intensity of thermal stress, suggesting that factors other than temperature may have influenced the differential response of octocoral microbiomes at different sampling sites.
Conclusions
Our results indicate that tissue loss in octocorals is not directly caused by the decline of the main bacterial symbionts but by the proliferation of opportunistic and pathogenic bacteria. Our findings thus underscore the significance of considering both relative and absolute quantification approaches when evaluating the impact of stressors on coral microbiome as the relative quantification does not accurately depict the actual changes in the microbiome. Consequently, this research enhances our comprehension of the intricate interplay between host organisms, their microbiomes, and environmental stressors, while offering valuable insights into the ecological implications of heatwaves on marine animal forests.
Corallium rubrum, Paramuricea clavata, Marine heatwaves, Climate change, Bacterial communities, Holobiont, Endozoicomonas, Spirochaetaceae, Gene expression, 16S rRNA gene sequencing, qPCR
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Publisher's official version | 19 | 6 Mo | ||
Figure S1. Temperature regime in 2022 and in the past 20 years in Portofino. Seawater temperature at 15 m, 30 m, and 35 m depth during the 2022 heatwaves (A), and number of exposure ... | - | 4 Mo | ||
Table S1. Mortality study. Table S2. Sequencing results. Table S3. DADA2 pipeline outputs. Table S4. ASV table. Table S6. Metadata. Table S7. Alpha diversity esults and statistical analysis.... | - | 3 Mo | ||
Table S5. Fasta file containing the sequences of each ASV. | - | 5 Mo | ||
Table S11. Fasta file containing the alignments between qPCR primers targeting Vibrio and ASV sequences. | - | 90 Ko | ||
Table S12. Fasta file containing the alignments between qPCR primers targeting Endozoicomonas and ASV sequences. | - | 29 Ko |
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