It is a shame that inequality has become sharper during our constitutional democracy than during apartheid.
enjoy mussels – steamed in white wine with garlic or in paella? You might want
to stop reading right now. Otherwise, I’m afraid I might ruin your appetite.
of us who are able to order mussel dishes in fancy restaurants have probably
not really felt the impact of climate change and the associated consequences of
humanity’s reliance on fossil fuels on a personal level quite yet. We tend to
be able to avoid those. Depriving us of mussels, however, may just open some
eyes to the realities of the growing global crisis we find ourselves in.
culprit is something called ocean acidification – you might have seen me rant
about it in the past. The carbon dioxide we are releasing into the atmosphere when
we burn oil, coal and natural gas doesn’t just act as a greenhouse gas that
causes global warming, some of it also dissolves in seawater. As it does so, it
increases the acidity (i.e. lowers the pH level) of the water and that is
starting to have far-reaching effects on the oceans.
that rely on skeletons or shells composed of a calcium carbonate as part of
their structure are directly impacted. As the seawater becomes gradually more
acidic (it’s currently still slightly alkaline on average with a pH of about
8), fewer and fewer of the carbonate ions the creatures need to extract from it
for building purposes are available, resulting in thinner and more fragile
skeletons and shells. You can guess where this is leading in the case of
A study published in June shows that the shells of Californian mussels are getting
thinner. The largest mussel shells in Native American archaeological sites
dating back to more than 2000 years ago are over 90% thicker than their modern
counterparts. Shells of mussels collected in the area in the 1970s are, on
average, around 32% thicker than those found today.
simple conclusion: mussels are producing less shell material now than they used
to in the past. The most likely explanation: ocean acidification.
should we care about the thickness of mussel shells? We eat the mussel flesh, not
provide a protective armour for mussels that shields them from predators like
marine snails specialised to drill through them. Thinner shells will make the
sails’ job easier and the mussels more vulnerable.
then there are the abrasive, highly energetic conditions in the areas of the
oceans that mussels inhabit – shallow tidal zones that are constantly battered
by strong currents, tides, storm surges and waves. Thinner shells will mean
higher fatality rates and fewer mussels reaching maturity.
acidic seawater isn’t just interfering with mussels’ ability to produce sturdy
shells, it’s also likely the affect the strength with which they’re able to
attach themselves to hard substrates like the surface of rocks.
laboratory research conducted at the University of Washington suggests that
when ocean water acidity drops below a pH level of 7.6 the adhesive strength of
the glue with which mussels secure themselves in place will diminish.
important, because it makes them more likely to be dislodged from their normal
habitats and washed to calmer areas where they are more exposed to predatory
snails, fish, sea stars and crabs. It also creates a problem for commercial
mussel farmers who rely on mussels’ ability to attach themselves to ropes
suspended in the sea.
to upwelling and local productivity, our seawater in Washington is already at a
baseline of pH 7.8,” says professor Emily Carrington, one of the scientists
involved in the research. “Moreover, mussels live in highly dynamic coastal
environments that routinely fluctuate up or down 0.5 pH units".
fantastic prospects for the future of mussel eating. But that shouldn’t really
be our biggest concern. The disappearance of these creatures will have more
significant effects on nature than on the menus of seafood joints.
because mussels are a so-called foundation species in many shallow marine
environments. The extensive mussel beds they create provide ecosystems in which
communities of hundreds of diverse, interdependent species are able to thrive.
Damage the mussels and you endanger all of their many associates.
to professor Cathy Pfister, the lead author of the study comparing mussel shell
thickness over time, "the California mussel is a common species along the
entire west coast of the United States and their fate will be linked to that of
a rich diversity of predators, including sea stars and sea otters, as well as
myriad species that are part of the mussel bed habitat”.
- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
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