The stable microbiome of inter and sub-tidal anemone species under increasing pCO2

Abstract

Increasing levels of pCO₂ within the oceans will select for resistant organisms such as anemones, which may thrive under ocean acidification conditions. However, increasing pCO₂ may alter the bacterial community of marine organisms, significantly affecting the health status of the host. A pH gradient associated with a natural volcanic vent system within Levante Bay, Vulcano Island, Italy, was used to test the effects of ocean acidification on the bacterial community of two anemone species in situ, Anemonia viridis and Actinia equina using 16 S rDNA pyrosequencing. Results showed the bacterial community of the two anemone species differed significantly from each other primarily because of differences in the Gammaproteobacteria and Epsilonproteobacteria abundances. The bacterial communities did not differ within species among sites with decreasing pH except for A. viridis at the vent site (pH = 6.05). In addition to low pH, the vent site contains trace metals and sulfide that may have influenced the bacteria community of A. viridis. The stability of the bacterial community from pH 8.1 to pH 7.4, coupled with previous experiments showing the lack of, or beneficial changes within anemones living under low pH conditions indicates that A. viridis and A. equina will be winners under future ocean acidification scenarios.

Figure 1. Map of sites sampled along the shoreline of Levante Bay, Vulcano Island Italy.

Figure modified from Horwitz et al..

Figure 2. Shannon diversity index of bacterial species found within samples of Anemonia viridis and Actinia equina along the pH gradient of Levante Bay, Vulcano, Italy (R = reference site, S1 = site 1, S2 = site 2, S3 = site 3, V = vent site).

ND represents no data because A. equina was not found within the vent site.

Figure 3. NMDS Ordination plot of the bacterial communities of Anemonia viridis and Actinia equina (stress = 0.18).

Black symbols represent samples of A. viridis, whereas grey symbols represent samples of A. equina. Open black ovals represent 95% confidence intervals of the NMDS analysis.

Figure 4

Relative abundances of bacterial classes present in (a) Anemonia viridis and (b) Actinia equina collected at different sites along a pH gradient in Levante Bay, Vulcano, Italy (R = reference site, S1 = site 1, S2 = site 2, S3 = site 3, V = vent site). Bacteria present in <3% relative abundance are grouped within ‘others’.

Figure 5

NMDS ordination plots of bacterial community composition by OTUs for (a) Anemonia viridis (stress = 0.13; n = 3 per site, R = reference site, S1 = site 1, S2 = site 2, S3 = site 3, V = vent site) and (b) Actinia equina (stress = 0.11; n = 3 per site, R = reference site, S1 = site 1, S2 = site 2, S3 = site 3). Open black ovals represent 95% confidence intervals of the NMDS analysis.

Figure 6

Relative abundance of (a) Alphaproteobacteria, (b) Gammaproteobacteria, (c) Bacilli, and (d) Epsilonproteobacteria present in Anemonia viridis. Parentheses after the Genus name indicate percent homology of identification (R = reference site, S1 = site 1, S2 = site 2, S3 = site 3, V = vent site). Bacteria present in <3% relative abundance are grouped within ‘others’.

Figure 7

Relative abundance of (a) Alphaproteobacteria, (b) Gammaproteobacteria, (c) Bacilli, (d) Epsiolonproteobacteria present in Actinia equina. Parentheses after the Genus name indicate percent homology of identification (R = reference site, S1 = site 1, S2 = site 2, S3 = site 3). Bacteria present in <3% relative abundance are grouped within ‘others’.