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What have we learnt from plankton?
Click image to enlarge |
Plankton inhabit various areas
of the oceans at different times of the year.
Their distribution is not the same all the
year round. Plankton inhabit areas that have
the required temperature, sunlight hours and
nutrients for the species. Look at the maps
opposite. You can see that the zooplankton
copepods Calanus finmarchicus lives
in colder waters than Calanus helgolandicus.
Each species has a clearly defined distribution.
Calanus finmarchicus used to inhabit
large areas of the North Sea until recently,
when its numbers in the region started to
decline. Is the North Sea getting warmer?
See how the distribution differs between
the phytoplankton species Ceratium furca
and Ceratium arcticum.
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At SAHFOS we have extensive plankton
distribution data collected over the last 70 years.
We are beginning to see changes in the distribution
of many more plankton species. Some species are
vacating areas of the oceans where they once inhabited
in large numbers. What is causing this? And what
are the effects going to be on other marine organisms
who rely on plankton for their food?
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Opposite is an
example of knock on effects in the marine
food chain. Looking at the top graph you can
see that the phytoplankton starts to decline
in numbers, which in turn affects the copepod
zooplankton, the fish (herring) and the Kittiwake
birds that feed on the fish. Whilst the plankton
communities may not suffer long term effects
and make a quick recovery, it takes longer
for the herring and Kittiwake populations
to make the same recovery. This is because
they are more complex organisms (take longer
to reach sexual maturity and reproduce). This
shows how the small changes in the marine
environment can have a magnifying effect through
the trophic levels of the food chain. A decline
in an animal like the basking shark could
have devastating effects on the population.
Click image to enlarge
Take a look at our
Food Chain Fact sheet and try our
Food Chain questions
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| The oceans cover more than 75%
of the earth’s surface and they support the
greatest diversity of life on earth. The deepest
parts of the oceans have barely begun to be
explored, and new life forms are being discovered
every year by deep-sea submersibles. In a world
where human induced effects are thought to be
accelerating, it is very important that we monitor
changes that could alter the marine world we are
only just discovering. |
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