Mussels and Oysters Threatened by Ocean Acidification
EcoPolis
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Mussels and Oysters Threatened by Ocean Acidification
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A large quantity of anthropogenic CO2 emissions has been stored in the
oceans, thus making them more acidic. Consequently, ocean pH has
experienced some variations since the beginning of the industrial age,
with a decline of 0.1 units. It is predicted that it will fall by a
further 0.4 units by the end of the century. Sea water acidification
will lead to a shift in the carbonate system equilibrium towards
higher CO2 and lower carbonate ion concentrations.
Several marine organisms such as coral reefs, coralline algae and
molluscs produce calcareous skeletons or shells (calcifying
organisms). They rely on steady carbonate ion concentrations in order
to produce the calcium carbonate needed to develop their shells.
Previous studies have shown how this pH decrease can slow up the
production of calcium carbonate by marine organisms such as coral,
algae and phytoplankton. Nevertheless, few studies have investigated
the detrimental effect of acidic waters on bivalves such as mussels
and oysters, especially within the range of atmospheric CO2 values
projected by the Intergovernmental Panel on Climate Change (IPCC).
As part of the EU-funded research projects MARBEF1 and CARBOOCEAN IP1,
Dutch and French scientists have recently investigated the impact of
elevated CO2 on mussel and oyster calcification. To this end, the
researchers used tanks with controlled seawater to observe these two
species of shellfish, and in particular calcification rates, as
greater amounts of CO2 were added.
Their findings suggest that, like other calcifying organisms, oysters
and mussels are seriously threatened by a change in the pH level of
the world's seas. They found that the ability of mussels and oysters
to produce shell material may decrease by 25% and 10% respectively in
seawater with CO2 levels of 740 parts per million per volume (ppmv),
as expected for the year 2100 according to the IPCC scenarios. They
also observed that when CO2 reached 1,800 ppmv, mussel shells started
to dissolve.
These findings may have important consequences in the future, given
the important role that mussels and oysters play in the environment in
governing energy and nutrient flows in coastal ecosystems, providing
habitats for other species, and constituting important food sources
for birds. Any decline in these species of shellfish would have major
consequences for coastal biodiversity.
Furthermore, these two species represent a large part of worldwide
aquaculture production. Indeed, for the last 30 years, global
shellfish production has increased by approximately 8% annually. In
2002, it reached 11.7 million tonnes, corresponding to a commercial
value of €7.9 billion. The pacific oyster, the one investigated in
this study, was the most cultivated species in 2002 (10.8% of the
total world aquaculture production). The predicted decrease in
calcification will probably cause important economic losses in the
sector.
Finally, the authors highlight that in order to fully assess the
impacts of ocean acidification, further investigation on the adaptive
responses of these organisms to long term CO2 enrichment is required.
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1The MARBEF project “MARine Biodiversity and Ecosystem
Functioning” (http://www.marbef.org) and the CARBOOCEAN IP project
“CarboOcean Integrated Project- Marine carbon sources and sinks
assessment” (http://www.carboocean.org) are supported by the European
Commission under the 6th Framework Programme within the thematic
programme “Sustainable development, global change and ecosystems”.
(Source: F. Gazeau et al. (2007) «Impact of elevated CO2 on shellfish
calcification», Geophysical Research Letters 34, doi:
10.1029/2006GL028554)
Contact: f.ga...@nioo.knaw.nl