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New
research on Antarctic krill (Euphausia superba), a shrimp-like
animal at the heart of the Southern Ocean food chain,
reveals behaviour that shows that they absorb and transfer
more carbon from the Earth's surface than was previously
understood. The results are published this week in the
journal Current Biology.
Scientists from British Antarctic Survey (BAS) and Scarborough
Centre of Coastal Studies at the University of Hull discovered
that rather than doing so once per 24 hours, Antarctic
krill 'parachute' from the ocean surface to deeper layers
several times during the night. In the process they inject
more carbon into the deep sea when they excrete their
waste than had previously been understood.
Lead Author Dr Geraint Tarling from BAS says, "We've
known for a long time that krill are the main food source
for whales, penguins and seals, but we had no idea that
their tactics to avoid being eaten could have such added
benefits to the environment. By parachuting down they
transport carbon which sinks ultimately to the ocean floor
– an amount equivalent to the annual emissions of
35 million cars – and this makes these tiny animals
much more important than we thought."
Krill feed on phytoplankton near the ocean surface at
night but sink deeper in the water column during the day
to hide from predators. By knowing how these animals behave,
we can understand better the contribution they make to
removing carbon from the Earth's atmosphere and upper
ocean.
NOTES TO EDITORS:
Satiation gives krill that sinking feeling by Geraint
A. Tarling and Magnus L. Johnson is published in Current
Biology on 7 February 2006.
Antarctic krill (Euphausia superba), are shrimp-like
crustaceans that are one of the most important animals
in the Southern Ocean. They feed on phytoplankton and
are in turn eaten by a wide range of animals including
fish, penguins, seals and whales. Phytoplankon are the
starting point for the marine food chain and use photosynthesis
to extract carbon from carbon dioxide.
Krill live in the open ocean, mainly in large swarms
and reach particularly high numbers in Antarctica. The
migrations that they perform (called Diel Vertical Migrations,
DVM) are a way of transporting carbon to the ocean's interior
because they eat phytoplankton at the surface and excrete
their waste at depth. Antarctic krill can grow up to a
length of 6cm and can live for 5-6 years. They are one
of the largest protein resources on Earth and can be fished
easily with large nets for human consumption.
There is enough Antarctic krill to fill the total volume
of the new Wembley stadium 1500 times. Spread out on the
floor, they would cover the entire area of Scotland. The
total weight of Antarctic krill is calculated between
50-150 million tonnes.
The krill migrate from the ocean surface by fanning out
their swimming legs and enter a controlled descent, akin
to parachuting. The behaviour is most apparent when their
stomachs are full and may be an effective means of getting
out of harms way when they can eat no more.
Numbers of Antarctic krill have dropped by about 80%
since the 1970's. The most likely explanation is a dramatic
decline in winter sea-ice. Krill feed on the algae found
under the surface of the sea-ice, which acts as a kind
of 'nursery'. The Antarctic Peninsula, a key breeding
ground for the krill, has warmed by 2.5°C in the last
50 years, with a striking decrease in sea-ice. It is not
fully understood how the loss of sea-ice there is connected
to the warming, but could be behind the decline in krill.
The study was carried out aboard the British Antarctic
Survey ship RRS James Clark Ross from December 2004 –
January 2005 around the islands of South Georgia in the
South Atlantic. The krill were caught with nets and transferred
to tanks for observations. The tanks were continuously
supplied with water (and therefore food) from the sea
surface.
British Antarctic Survey is a world leader in research
into global issues in an Antarctic context. It is the
UK's national operator and is a component of the Natural
Environment Research Council. It has an annual budget
of around £40 million, runs nine research programmes
and operates five research stations, two Royal Research
Ships and five aircraft in and around Antarctica. More
information about the work of the Survey can be found
at: www.antarctica.ac.uk
Centre for Coastal studies is based at the Scarborough
campus, at the University of Hull. The Centre for Coastal
Studies is a small but vibrant centre, specialising in
teaching and research with a strong emphasis on fieldwork.
The centre attracts around 50 students a year from a wide
range of backgrounds who study degrees in Coastal Marine
Biology, Environmental Science and Ecology. Students acquire
strong theoretical knowledge of their subject combined
with skill and expertise in the field. Academics and postgraduates
in the centre are currently working on a diverse range
of topics including intertidal ecology, krill morphometrics,
fisheries management and tropical fish biology. For more
information visit: www.ccs.hull.ac.uk
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