Published in Abstracts of International Coral Reef Symposium 2008
The Host as a Habitat Divided
Nathan D. Olson, University of Hawaii at Hilo HI, USA
Tracy Ainsworth, University of Queensland, Queensland, AUS
Mali’o Kodis, University of Hawaii at Hilo, USA
Ruth D. Gates, Hawaiian Institute of Marine Biology HI, USA
Misaki Takabayashi, University of Hawaii at Hilo HI, USA
Scleractinian corals are now viewed as complex holobiont systems comprising the animal
host and a consortium of microbial symbionts. This conceptual shift has led us to
consider the coral host as a habitat. When viewed as a habitat, the coral can be
subdivided into three compartments or interacting systems; the endolith, tissue, and
mucus. Microbes in these compartments are speculated to be linked to the rest of the
holobiont community through nitrogen interdependency. In order to assess the identity
and potential roles of symbiotic microbes in the nitrogen cycle of the coral holobiont, we
examined the microbes present in each of these three compartments of Hawaiian corals of
genus Montipora. The prevalence of endolithic fungi in Montipora capitata was
analyzed across an environmental gradient present in Kaneohe Bay through the use of
culturing techniques. The results indicate a mean prevalence of 75% (n = 120) with no
statistically significant difference in prevalence at sites that cross the gradient. The mean
prevalence of endolithic fungi is higher in Kaneohe Bay, Hawaii than reported for other
reef systems. Within the coral tissue compartment, nifH sequence data obtained from M.
capitata tissue indicates the presence of bacteria capable of nitrogen fixation belonging to
the taxa Vibrio. Fluorescent in situ hybridization of tissue sections of M. capitata using
probes specific to the bacterial genus Vibrio revealed that the bacteria are localized
within the coral epidermal tissue layer. Lastly, the diversity of microbial ribotypes
present in the mucus of M. patula was analyzed using molecular approaches.
Collectively, these data contribute a more thorough characterization of the complexity of
microbial communities in corals and allow for the generation of hypotheses regarding the
role of each microbial member in the nitrogen cycling within the coral holobiont.