Changes in coral microbial communities in response to a natural pH gradient

Abstract

Surface seawater pH is currently 0.1 units lower than pre-industrial values and is projected to decrease by up to 0.4 units by the end of the century. This acidification has the potential to cause significant perturbations to the physiology of ocean organisms, particularly those such as corals that build their skeletons/shells from calcium carbonate. Reduced ocean pH could also have an impact on the coral microbial community, and thus may affect coral physiology and health. Most of the studies to date have examined the impact of ocean acidification on corals and/or associated microbiota under controlled laboratory conditions. Here we report the first study that examines the changes in coral microbial communities in response to a natural pH gradient (mean pH T 7.3-8.1) caused by volcanic CO 2 vents off Ischia, Gulf of Naples, Italy. Two Mediterranean coral species, Balanophyllia europaea and Cladocora caespitosa, were examined. The microbial community diversity and the physiological parameters of the endosymbiotic dinoflagellates (Symbiodinium spp.) were monitored. We found that pH did not have a significant impact on the composition of associated microbial communities in both coral species. In contrast to some earlier studies, we found that corals present at the lower pH sites exhibited only minor physiological changes and no microbial pathogens were detected. Together, these results provide new insights into the impact of ocean acidification on the coral holobiont.

New insights into the genetic diversity of zooxanthellae in Mediterranean anthozoans

“…Cladocora caespitosa was also included in our study considering samples from the Western Mediterranean (Castellón and Tarragona, Balearic Sea); however, they harbor the Symbiodinium sp. "Temperate A" clade, which differs from that found by LaJeunesse et al (2012) and Meron et al (2012). This regional variation in Symbiodinium associations within the same host species has been previously reported in the Western Atlantic as well as the Indo-Pacific Oceans, suggesting that those changes might be dependent on regional environmental conditions (Rodriguez-Lanetty et al 2001;Savage et al 2002).…”

“…Symbiodinium phylotype B has also been described by (2012) found phylotype B2 in three species of scleractinians from the coast of Israel in the Eastern Mediterranean Basin: Oculina patagonica, Cladocora caespitosa and Madracis pharensis. In addition, Meron et al (2012) found this same phylotype in Balanophyllia europaea and C. caespitosa in the Central Mediterranean (Iscchia Island, Southern Tyrrhenian Sea). However, these authors also found clade "Temperate A" in some individuals of B. europaea from the same locality.…”

Responses of Coral-Associated Bacterial Communities to Local and Global Stressors

“…For example, O. faveolata's microbiome did not significantly shift when the host bleached (Tracy et al, 2015). Furthermore, coralassociated microbial communities did not undergo major shifts when transplanted to a natural lower pH environment and did not harbor microbial pathogens (Meron et al, 2012). This study (Meron et al, 2012), suggests that for these two coral species (i.e., Balanophyllia europaea and Cladocora caespitosa), reduced pH does not pose a significant threat to coral health.…”

“…Furthermore, coralassociated microbial communities did not undergo major shifts when transplanted to a natural lower pH environment and did not harbor microbial pathogens (Meron et al, 2012). This study (Meron et al, 2012), suggests that for these two coral species (i.e., Balanophyllia europaea and Cladocora caespitosa), reduced pH does not pose a significant threat to coral health. Importantly, environmental conditions can buffer these microbiome changes, specifically with high water flow buffering coral microbiome changes under high temperatures (Lee et al, 2017).…”

“…However, this is not always the case, as other studies have demonstrated no significant change or a decrease in microbial diversity under these three stressors (Meron et al, 2012;Tracy et al, 2015;Morrow et al, 2017). These conflicting results likely are the result of variability in coral microbiome responses across coral host species, locations and stressors.…”