Geoscience Reference
In-Depth Information
chemical cycle will be reduced in number
and effectiveness by even a small increase
in acidity, which will greatly disturb marine
ecosystems. The tiny organisms that make
up plankton, some of the most important
elements of the food chain, will be particu-
larly affected. These include the coccolitho-
phorids (plants), foraminifera (single-celled
organisms), and pteropods (tiny snails also
known as sea butterflies), all of which use
CaCO
3
in their shells.
The pteropods are especially suscep-
tible to acidification because their thin,
fragile shells are made up of the relatively
unstable CaCO
3
mineral aragonite. Ptero-
pods are a base of the food chain, which
extends from zooplankton to salmon to
whales. In the Southern Ocean pteropods
could disappear in this century, according
to some studies. A number of commercial
species including cod and salmon rely on
pteropods in northern waters. A study in
Alaskan waters estimates that a 10% de-
crease in pteropod abundance would lead
to a 20% reduction in the weight of adult
salmon that depend on plankton for food
at one stage in their life cycle.
Coral reefs, which are also largely ara-
gonite, will be damaged as acidification
results in less robust, more vulnerable pol-
yps. Disruption of the coral reef ecosystem,
where fully one-third of all marine species
exist, will have a particularly large impact
on shallow water marine life over large ar-
eas of the ocean. Complicating the survival
of the world's coral reefs is the simultane-
ous warming of ocean temperature and
the rising sea level. Not helping matters
is widespread human-caused pollution,
plus events like the grounding in 2010 of
a Chinese freighter running at full speed
into the Great Barrier Reef of Australia and
the oil spill in the same year in the Gulf of
Mexico, which totaled around five million
barrels.
There are two methods by which marine
organisms build carbonate skeletons. The
first involves scallops, oysters, some snails,
and coral that exert little biological control
over the precipitation of CaCO
3
in their
skeletons. These creatures are dependent
upon the saturation or super-saturation
in seawater of the mineral they use, which
means that they will be particularly sus-
ceptible to any acidification and reduction
of carbonate in seawater. Very often the
juveniles of these organisms are particu-
larly sensitive to acidification. The second
method of building skeletons involves ani-
mals having more biological control of cal-
cification (as opposed to inorganic chemi-
cal control in the first method); hence the
composition of seawater is less important
to these organisms.
Of course, acidification involves lots
of uncertainties, and there will be unex-
pected impacts. There is even some con-
cern that acidification will proceed to the
point where concrete structures in the sea
such as piers and seawalls will be weakened
by the dissolution of cement. Aquarium
studies have shown that the giant Pacific
Humboldt squid becomes sluggish and has
difficulty breathing in acidic waters. A lab-
