Without plankton there wouldn’t be polar bears on
the ice.
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| Phytoplankton and copepods are the first two steps in the plankton food chain |
In the sea, the plankton begin the marine food chain.
Microscopic phytoplankton (tiny plant-like cells) use the sun's energy to
combine carbon dioxide and water to create sugar and oxygen in the process
known as photosynthesis. Despite being tiny (each phytoplankton cell is smaller
in diameter than a strand of human hair), they are so numerous that they
account for about 50% of all photosynthesis on Earth. And here, tiny creatures
and big numbers start to mix, since 50% of all photosynthesis equates to about 50
billion tonnes of carbon each year, or about 125 billion tonnes of sugar!
The phytoplankton are the food of herbivorous zooplankton
(animal plankton) in turn eaten by carnivorous zooplankton. Together all the
plankton are the food for fish, which in turn are eaten by other sea creatures
such as seabirds, sharks, and seals, in their turn eaten by larger predators
like killer-whales. The plankton are also the food source of some of the
largest mammals on Earth, the baleen whales. In this way the plankton food web
underpins and determines the amount of life in the sea. Quite simply, without
the plankton there would not be any fish in the sea for you, me or other
creatures to eat, and so that is why there wouldn't be any polar bears on the
ice.
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| The author and plankton scientist Dr Richard Kirby |
Of course, as well as eating fish, we also consume many
marine creatures that had a larval life in the plankton such as shrimps, crabs,
and mussels etc. In some countries we also eat plankton too, such as Antarctic
krill that is eaten in Japan as Okami. In fact, in Britain during the Second
World War there were trials in Scottish sea lochs to determine whether large static
nets could harvest sufficient plankton to supplement the national diet should
food become scarce. While those early Scottish trials in the 1940s proved
unsuccessful, today, a commercial copepod harvest for food for aquaculture occurs
in some Norwegian Fjords by using large nets towed by trawlers.
Now, we need to pay attention to the plankton more than
ever. Living at the sea surface the plankton are particularly sensitive to
changes in sea surface temperature, which is influenced by the air temperature
above. (We often forget that we can engineer our thermal environment unlike
other life on Earth that lives where the temperature suits it best.) My
research and that of other plankton scientists, is revealing that rising sea
temperatures due to current climate change are altering the abundance, distribution,
and seasonality of the plankton throughout the oceans with ensuing
ramifications for the marine food chain, our commercial fisheries, and the
wider marine ecosystem.
Unfortunately, in this short blog there wasn't time to tell you how the
plankton do so much more than just support the marine food web. However, you
can find out how much more by watching my short film Ocean Drifters, a secret world beneath the waves, narrated by David
Attenborough: https://vimeo.com/84872751
Dr Richard Kirby is a British plankton expert, scientist, author and speaker. Follow Richard @planktonpundit on Twitter. You can see more images of plankton and learn more about them in Dr Richard Kirby’s book “Ocean Drifters, a secret world beneath the waves” available on Amazon and as an iBook.
