Effects of ocean acidification on the diversity and activity of heterotrophic marine microorganisms - Ocean Acidification - page 95

theory of evolution (Rosenberg et al. 2007 ), changes
in the microbial community composition could be a
means to counterbalance environmental changes.
Although data are missing, there is increasing evi-
dence that microorganisms are strongly involved in
carbon and nutrient cycling in the holobiont. Thus,
corals (and sponges) may be able to partly adapt to
ocean acidii cation via changes in the structural and
functional diversity of associated microorganisms.
The microbial community associated with a
zooxanthellate coral showed shifts towards a
bacterial community composition characteristic of
dead corals when exposed to higher p CO 2 levels
(Vega Thurber et al. 2009). This seems to contradict
the probiotic coral hypothesis of Reshef et al. ( 2006 ),
but one must keep in mind that the experiment was
performed using a strong decrease in pH and ran
over a short time frame, which might have pre-
vented the detection of adaptation.

in the real world, studies on acclimation and adap-
tation will be crucial for an evaluation of the per-
formance of microorganisms in a high-CO 2 ocean.
An overall conclusion of microbe-related ocean
acidii cation studies is that only a few environments
have been studied. Among the systems not yet
studied or barely studied with respect to microbe
interactions are the dark ocean, sediments, as well
as microorganisms associated with benthic animals,
macrophytes, zooplankton, and i sh. To the best of
our knowledge, no study has been performed on
microbial pathogens and (heterotrophic) symbionts.
Also, studies on some crucial processes such as
prokaryotic respiration and growth efi ciency are
missing. Data from in-depth sequencing studies are
not available yet. Thus, many potential effects of
ocean acidii cation on viruses and heterotrophic
microbes remain to be investigated.

5.5 Acknowledgements

5.4.2 Acclimation, adaptation, and perspectives

This work is a contribution to the 'European Project
on Ocean Acidii cation' (EPOCA) which received
funding from the European Community's Seventh
Framework Programme (FP7/2007-2013) under
grant agreement no. 211384. It was also supported
by the projects ANR-AQUAPHAGE (no. ANR 07
BDIV 015-06) and ANR-MAORY (no. ANR 07
BLAN 0116) from the French Science Ministry. The
comments of Carol Turley and Ulf Riebesell on an
early draft of this chapter are much appreciated.

Potential evidence for acclimation (i.e. the adjust-
ment to environmental change by physiological
and morphological change) of bacteria to ocean
acidii cation comes from pH i regulation in a Vibrio
strain (Labare et al. 2010 ). Adaptation, the adjust-
ment to environmental change by genetic change,
is probably faster in microbes than for multicellular
marine organisms. This is due to their short
generation time of only a few days which allows
for thousands of generations within the projected
ocean acidii cation scenarios, hence increasing the
potential for accumulation of mutations, and (at
least for prokaryotes) due to the efi cient mecha-
nisms of lateral gene transfer. Genomics, trans-
criptomics, proteomics, and assessment of the
expression of specii c marker genes for crucial
functions are among the most promising methods
that are available, or are on the verge of develop-
ment, for investigating potential of acclimation and
adaptation. In this context, it is necessary to note
that no data are available for long-term experi-
ments, which could shed light on potential accli-
mation and adaptation. Since the currently used
experimental approaches involve perturbation
experiments with a p CO 2 or pH 'shock' which does
not mimic the gradual increase in p CO 2 that occurs

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