Scientific data concerning the effects of
increased CO2 concentration and decreased
pH in seawater on the marine organisms are
essential for both anticipating the future
impacts of increasing atmospheric CO2
concentration and assessing the effects of
deep-sea CO2 sequestration. In this study, I
attempted to clarify both lethal and sub-lethal
effects of increased CO2 concentration to the
marine animals. To attain this aim, I study the
long-term effects of increased seawater CO2
concentration on the meiofauna community
(Chapter 1), lethal and sub-lethal effects on
planktonic copepods (Chapter 2) and effects
on the early development of sea urchin
embryos (Chapter 3).

As a results, present study revealed that; 1.
The marine organisms tended to be affected
more severely as the CO2 concentration in
seawater increased, 2. Sub-lethal effects of
CO2 such as effects on reproduction,
fertilization, cleavage and morphology could
be seen at CO2 concentration that did not
cause lethal effects, 3. Early stage embryos
were more sensitive than adult organisms to
the elevation of CO2, 4. The seawater acidified
by CO2 was more toxic than seawater
acidified by strong acids, and 5. The
calcification rate decreased with increased
CO2 concentration in the seawater.

The ocean is known to be a vast reservoir of
CO2 due to the biological activity by the marine
organisms, and plays a critical role in the
global CO2 cycle. One likely future scenario is,
change in the biological activities of marine
animals due to increased atmospheric CO2,
which might in turn, slow down the vertical flux
of organic carbon and ultimately change the
oceanic carbon cycle. This might result in
negative feedback to the atmospheric CO2
concentration and in the terrestrial ecosystem.
Present results also have implications that
deep-ocean CO2 sequestration strategies
may affect the deep-sea animals. Therefore, it
is assumed that both the elevation of
atmospheric CO2 concentrations and direct
injection of CO2 into the deep sea would
directly affect the marine organisms and result
in change of the marine ecosystem.