Data from: Dominance of Endozoicomonas bacteria throughout coral bleaching and mortality suggests structural inflexibility of the Pocillopora verrucosa microbiome

The functional importance of Symbiodinium algal endosymbionts and a
diverse suite of bacteria for coral holobiont health and functioning is
widely acknowledged. Yet, we know surprisingly little about microbial
community dynamics and the stability of host-microbe associations under
adverse environmental conditions. To gain insight into the stability of
coral host-microbe associations and holobiont structure, we assessed
changes in the community structure of Symbiodinium and bacteria associated
with the coral Pocillopora verrucosa under excess organic nutrient
conditions. Pocillopora-associated microbial communities were monitored
over 14 days in two independent experiments. We assessed the effect of
excess dissolved organic nitrogen (DON) and excess dissolved organic
carbon (DOC), the latter which was published recently. Exposure to excess
nutrients rapidly affected coral health, resulting in two distinct stress
phenotypes: coral bleaching under excess DOC on the one hand and severe
tissue sloughing (> 90 % tissue loss resulting in host mortality)
under excess DON. These phenotypes were accompanied by structural changes
in the Symbiodinium community. In contrast, the associated bacterial
community remained remarkably stable and was dominated by two
Endozoicomonas phylotypes, comprising on average 90 % of bacterial
sequences. This dominance of Endozoicomonas even under conditions of coral
bleaching and mortality suggests the bacterial community of P. verrucosa
may be rather inflexible, and thereby unable to respond or acclimatize to
rapid changes in the environment, contrary to what was previously observed
in other corals. In this light, our results add important detail to our
understanding of the structural flexibility and stability of the coral
holobiont. Coral holobionts might occupy structural landscapes ranging
from highly flexible to rather inflexible with consequences for their
ability to respond to environmental change.