Porcelain crab | Adam Paganini
The combined effect of rising temperatures and a
more acidic ocean will make it harder for seashore crabs to grow
and reproduce, a new study finds.
The results suggests that other marine species could be affected
too, the researchers say.
The oceans absorbs around 30
per cent of the carbon dioxide we emit into the
atmosphere. When carbon dioxide dissolves in water, carbonic acid
is produced, which makes the oceans more acidic. The oceans have
become around 26 per cent more acidic since the industrial
revolution and this is projected to increase further under
all scenarios of the Intergovernmental Panel
on Climate Change.
New research, published in The
Journal of Experimental Biology, studies the impact of ocean
acidification and higher air temperatures on the porcelain
crab, which lives in rocky shorelines on the coasts of the
Indian and Pacific Oceans.
The results show that warmer, more acidic
conditions mean the crabs have to put a greater proportion of
energy into the basic functions of living and breathing, leaving
less for anything else.
This could be an indicator for other species in
the 'intertidal zone', or seashore, too. As co-author, Professor
Jonathon Stillman, explains: "future intertidal zone
animals may experience reduced rates of growth, behavior, or
High- and low-tides
studies have tested the impact of constant
high temperatures and acidity on sea creatures, this isn't typical
of the conditions on the seashore.
Air temperatures in the intertidal zone can
change by 20°C within six hours, while acidity levels can vary
between day and night and from one season to the next. This study
tests temperature and acidity that peak and fall during the
In order to test the crabs under these
conditions, researchers constructed a specially-designed aquarium,
which could simulate high- and low-tide as well as different
temperatures and acidity.
They simulated 'low-tide' in the aquarium for
seven hours each day, reducing the water and increasing the air
temperature. Then for five hours of 'high-tide' they submerged the
crabs with water and brought the air temperature back down. They
tested three scenarios of higher temperature and higher acidity (no
change, moderate change and extreme change).
After two and a half weeks in those conditions, the researchers
tested the metabolic rate and thermal tolerance of the crabs.
The findings show the combination of higher
temperatures and more acidic water cause the crabs' metabolic rate
to fall by as much as 25 per cent. You can see this by the green
line in graph A below. The metabolism of the crabs slowed down,
leaving them less energy to use in finding food, reproducing, or