Ocean acidification and calcareous plankton
Changes in temperature have direct consequences on many
physiological processes (e.g. oxygen metabolism, adult mortality,
reproduction, respiration, reproductive development) and control
virtually all life-processes from the molecular to the cellular and
from the regional ecosystem level to biogeographical provinces.
Temperature also modulates species interactions (e.g. competition,
prey-predator interactions and foodweb structures) both directly
and indirectly; ultimately, changes in temperatures caused by
climate change can lead to impacts on the biodiversity, size
structure, carrying capacity and functioning of the whole pelagic
ecosystem. While temperature has direct consequences on many
biological and ecological traits it also modifies the marine
environment by influencing oceanic circulation and by enhancing the
stability of the water column and hence nutrient availability.
Under many climate change scenarios, oceanic primary production is
predicted to decline due to nutrient limitation.
While temperature, light and nutrients are probably the most
important physical variables structuring marine ecosystems, the
pelagic realm will also have to contend with, apart from global
climate warming, the impact of anthropogenic CO2 directly
influencing the pH of the oceans. Evidence collected and modelled
to date indicates that rising CO2 has led to chemical changes in
the ocean which has led to the oceans becoming more acidic. Ocean
acidification has the potential to affect the process of
calcification and therefore certain planktonic organisms (e.g.
coccolithophores, foraminifera, pelagic molluscs) may be
particularly vulnerable to future CO2 emissions. Apart from climate
warming, potential chemical changes to the oceans and their effect
on the biology of the oceans could further reduce the ocean's
ability to absorb additional CO2 from the atmosphere, which in turn
could affect the rate and scale of climate warming.
Presently in the North Atlantic certain calcareous taxa are
actually increasing in terms of abundance, a trend associated with
climate shifts in the Northern Hemisphere temperature (see below
figure of foraminifera frequency). However, there is some observed
evidence from the Southern Ocean that modern shell weights of
foraminifera have decreased compared with much older sediment core
records with acidification being implicated (Nature Geoscience
(2009) doi:10.1038/ngeo460). It is not yet known how much of an
effect acidification will have on the biology of the oceans in the
21st century, whether rapid climate warming will override the
acidification problem, and whether or not species can buffer the
effects of acidification through adaptation. The CPR survey is
providing a critical baseline (both in space and time) and is
currently monitoring these vulnerable organisms in case in the
future these organisms begin to show negative effects due to
acidification.
Read more:
|
|
Contact at SAHFOS: Abigail McQuatters-Gollop
|
|
|
|
| The percent frequency of foraminifera (top) and coccolithophores (bottom) recorded on CPR samples. |
