Geoscience Reference
In-Depth Information
(e.g. [PAR 12, TAL 11]). While fertilization does not seem to be
affected by increases in seawater acidity (e.g. [VAN 12]), embryonic
and larval developments are very sensitive, with a decrease in size and
survival of larvae, an increase in the number of abnormal larvae and
an increased duration of the planktonic life stage (e.g. [GAZ 10]). The
larval stage is a key step in the lifecycle of mollusks; small
perturbations during the larval stage can compromise the sustainability
of mollusk populations. The success rate of the larval stage does not
exceed 2% in nature [BAY 76]; it is easy to understand that an
additional perturbation, such as ocean acidification, could have
disastrous consequences on these organisms. This is already the case
on the coast of California where deep-sea waters rich in CO
2
rise to
the surface due to a
seasonal
upwelling [FEE 08]. This natural
phenomenon is reinforced by ocean acidification and results in pH
levels detrimental to the development of Pacific oyster larvae
cultivated in hatcheries [BAR 12]. Intense collaboration between
researchers and the aquaculture industry has resulted in new
management techniques including the continuous monitoring of the
pH of the facilities. Seawater pumping is interrupted when the acidity
of the water exceeds a critical threshold.
We should stress that mollusks have colonized, over the course of
their evolution, very different environments and are even found in
extreme ecosystems such as deep hydrothermal vents, which can be
acidic (pH
NBS
as low as 5.36 [TUN 09]). It is, therefore, certain
that these organisms have the molecular and physiological capability
to resist such hostile environments. The question is whether
populations which have been exposed for thousands, or even
millions, of years to relatively high pH levels will be able to adapt to
the rapid increase (on the evolutionary scale) in seawater acidity. One
recent study has shown that the effect of ocean acidification on the
larvae of an Australian oyster is lessened when the breeders are
acclimated to elevated pCO
2
levels prior to reproduction [PAR 12].
Finally, as in other taxonomic groups, interactions between changes in
the carbonate chemistry and changes in other environmental
parameters, such as temperature and salinity, are poorly known for
mollusks.
