Abstract
All corals have a common structure: two tissue layers enclose a lumen, which forms the gastric cavity. Few studies have described the processes occurring inside the gastric cavity and its chemical and biological characteristics. Here, we show that the coral gastric cavity has distinct chemical characteristics with respect to dissolved O2, pH, alkalinity, and nutrients (vitamin B12, nitrate, nitrite, ammonium, and phosphate) and also harbors a distinct bacterial community. From these results, the gastric cavity can be described as a semi-closed sub-environment within the coral. Dissolved O2 shows very low constant concentrations in the deepest parts of the cavity, creating a compartmentalized, anoxic environment. The pH is lower in the cavity than in the surrounding water and, like alkalinity, shows day/night variations different from those of the surrounding water. Nutrient concentrations in the cavity are greater than the concentrations found in reef waters, especially for phosphate and vitamin B12. The source of these nutrients may be internal production by symbiotic bacteria and/or the remineralization of organic matter ingested or produced by the corals. The importance of the bacteria inhabiting the gastric cavity is supported by the finding of a high bacterial abundance and a specific bacterial community with affiliation to bacteria found in other corals and in the guts of other organisms. The findings presented here open a new area of research that may help us to understand the processes that maintain coral health.
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Acknowledgments
This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas for “Coral reef science for symbiosis and coexistence of human and ecosystem under combined stresses” (20121003) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan and by the Global Coral Reef Conservation Project of Mitsubishi Corporation, Japan. The author would like to thank the anonymous reviewers for their helpful comments to improve this manuscript.
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338_2011_831_MOESM1_ESM.eps
Supplementary figure: Rarefaction curve showing the coverage of the bacterial community diversity within the gastric cavity. The number of clones is the total of number of phylotypes sequenced and OTUs is the number of unique phylotypes identified (EPS 31 kb)
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Agostini, S., Suzuki, Y., Higuchi, T. et al. Biological and chemical characteristics of the coral gastric cavity. Coral Reefs 31, 147–156 (2012). https://doi.org/10.1007/s00338-011-0831-6
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DOI: https://doi.org/10.1007/s00338-011-0831-6