The impact of reduced pH on the microbial community of the coral Acropora eurystoma

Abstract

Rising concentrations of atmospheric carbon dioxide are acidifying the world's oceans. Surface seawater pH is 0.1 units lower than pre-industrial values and is predicted to decrease by up to 0.4 units by the end of the century. This change in pH may result in changes in the physiology of ocean organisms, in particular, organisms that build their skeletons/shells from calcium carbonate, such as corals. This physiological change may also affect other members of the coral holobiont, for example, the microbial communities associated with the coral, which in turn may affect the coral physiology and health. In the present study, we examined changes in bacterial communities in the coral mucus, tissue and skeleton following exposure of the coral Acropora eurystoma to two different pH conditions: 7.3 and 8.2 (ambient seawater). The microbial community was different at the two pH values, as determined by denaturing gradient gel electrophoresis and 16S rRNA gene sequence analysis. Further analysis of the community in the corals maintained at the lower pH revealed an increase in bacteria associated with diseased and stressed corals, such as Vibrionaceae and Alteromonadaceae. In addition, an increase in the number of potential antibacterial activity was recorded among the bacteria isolated from the coral maintained at pH 7.3. Taken together, our findings highlight the impact that changes in the pH may have on the coral-associated bacterial community and their potential contribution to the coral host.

Interactive network configuration maintains bacterioplankton community structure under elevated CO<sub>2</sub> in a eutrophic coastal mesocosm experiment

“…Ocean acidification also affects the community structure of bacteria associated with corals. It has been reported that the relative abundance of bacteria associated with diseased and stressed corals increased under decreasing pH conditions (Meron et al, 2011). A very limited number of studies focused on the effects of ocean acidification on isolated bacterial strains have also been reported.…”

Investigating the Driving Mechanisms Behind Differences in Bleaching and Disease Susceptibility Between Two Scleractinian Corals, Pseudodiploria Strigosa and Diploria Labyrinthiformis

“…In our experiments corals were exposed to increasing acidification, for a final pH of 7.7, for only eight weeks. Other acidification studies used lower pH values of 7.3 (Meron et al 2011) and6.7 (Vega Thurber et al 2009). In these studies, an increase in Alphaproteobacteria and decrease in Deltaproteobacteria and Bacteroidetes was detected within the SML at pH 7.3 (Meron et al 2011), and a decrease in Alphaproteobacteria and increase in Beta-, Delta-and Epsilonproteobacteria was detected at pH 6.7 (Vega Thurber et al 2009).…”

“…Other acidification studies used lower pH values of 7.3 (Meron et al 2011) and6.7 (Vega Thurber et al 2009). In these studies, an increase in Alphaproteobacteria and decrease in Deltaproteobacteria and Bacteroidetes was detected within the SML at pH 7.3 (Meron et al 2011), and a decrease in Alphaproteobacteria and increase in Beta-, Delta-and Epsilonproteobacteria was detected at pH 6.7 (Vega Thurber et al 2009). Although the current acidification study did not involve microbial analysis, and did not detect changes in the SML thickness, the changes in microbial populations detected in other studies suggest that the SML is affected by acidification in other ways.…”

“…In addition to the protective physical properties, the SML also contains a microbial community that is crucial to the health of the coral (Bythell and Wild 2011). In the past ten years many studies have focused upon the composition and role of this microbial community Kellogg 2004;Bourne 2005;Guppy and Bythell et al 2006;Littman et al 2009;Shnit-Orland and Kushmaro 2009;Vega Thurber et al 2009;Meron et al 2011;Sweet et al 2011). This body of research has led to the development of the coral probiotic hypothesis, stating that coral-associated microbes may serve to protect their host based on their ability to rapidly evolve protection mechanisms .…”

“…For example, increased temperature and acidification caused the SML-associated microbial functional gene community to change (Vega Thurber et al 2009), and microbial communities shifted significantly at a lowered pH of 7.3 (Meron et al 2011). It was not determined in these studies whether the observed microbial functional gene and community shifts occurred in response to the changes in environmental conditions, or due to altered properties of the SML under the influence of these factors, which secondarily influenced the microbial communities.…”