Geoscience Reference
In-Depth Information
Box 13.1 Ocean acidii cation and food security
'Food security exists when all people, at all times, have
physical and economic access to suffi cient, safe and
nutritious food that meets their dietary needs and food
preferences for an active and healthy life' ( Rome
Declaration on World Food Security and World Food Summit
Plan of Action 1996 ).
Demand for i sh and i shery products is projected to
expand from 133 million tonnes in 2001 to 183 million
tonnes by 2030 (FAO 1999). As world marine capture
i sheries are projected to stagnate, there will be a mismatch
between supply and demand which will need to be met
from other sources. The most likely candidate for supplying
the dei cit is the burgeoning industry of aquaculture which
is currently the fastest growing method of food production
in the world with 7% growth per annum (by value),
accounting for 47% of the world's food i sh supply in 2006
and valued at US$78.8 billion (FAO 2008).
Aquaculture, at present and for the foreseeable future,
relies heavily upon i sh meal as a food stock—effectively
using i sh to feed i sh. It is reported that for every
kilogram of i sh produced via aquaculture, up to 5 kg of
capture i sh are consumed by the process (Naylor et al.
2000). The species, caught in vast quantities, used for
aquaculture feedstock fall into the category of 'forage
i sh'—important links in ocean food chains and key
species for human consumption in some developing
countries. So, critics argue, aquaculture is no 'silver bullet'
or 'cure all' and is beset with its own challenges, amongst
them environmental damage and inefi cient use of
dwindling resources.
It can be seen that the demand for marine protein and
the available supply, including aquaculture, will be in a
delicate balance. The entire i sheries system and the
ecosystems associated with it are i nely tuned yet highly
pressured by i sheries and other stressors (Worm et al.
2006). Ocean acidii cation is yet another, although
perhaps more insidious, pressure on these limited
resources.
price of the substantial change to ocean chemistry
under consideration here. This invaluable role of
oceans in the earth's carbon cycle is performed by
a series of biogeochemical processes regulated by
marine organisms as well as the important physi-
cal processes of ocean mixing, tides, currents, and
air-sea exchange. The ability of microscopic plants,
phytoplankton, to i x CO
2
through photosynthesis
and transfer a proportion of it to the deep sea via
this 'biological pump' is a key part of the global
carbon cycle (see Chapter 12). It is a surprise to
many that oceans contribute around half of global
primary production (Field
et al.
1998 ), and while
this is mostly due to phytoplankton, larger marine
plants contribute as well. Any stressor reducing
ocean productivity and the biological pump could
have substantial feedback to climate (see Chapter
12). Marine microorganisms also play a less well
known role in regulation of other climate changing
gases such as dimethyl sulphide, methane, and
nitrous oxide (see Chapter 11).
In contrast, and importantly, the larger marine
plant communities such as mangroves, salt marshes,
and seagrass and kelp beds store carbon, known as
'blue carbon' for longer periods (Duarte
et al.
2005 ),
not unlike the 'green carbon' stores in forests, scrub-
lands, savannas, grasslands, and tundra on land.
These communities build up sediments rich in
organic carbon similar to soils under rainforests
( Nellemann
et al.
2009). As on land, these marine
ecosystems are degrading and shrinking, and this
natural 'blue carbon' store is reducing. Climate
change and ocean acidii cation are other pressures
on these carbon-binding ecosystems to add to those
of coastal development, aquaculture, and pollution.
There are calls for a global 'blue carbon' fund for the
protection and management of coastal and marine
ecosystems, not unlike the Reducing Emissions
from Deforestation and Degradation (REDD) initia-
tive (Angelsen 2008) to preserve the 'green carbon'
locked in rainforests, so that this marine carbon
store can be preserved and replenished.
13.3.3 Nutrient regulation
Sediments play a crucial role in the cycling of car-
bon and nitrogen through the biochemical activities
of microorganisms and the behaviour of larger
organisms that live in and on the sediments. Their
activities result in a release of nutrients from the
