Plankton: the air we breathe

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Though it’s not always visible to the naked eye, it’s the origin of our food, our fuel and the air we breathe.

Now, the French centre for scientific research (CNRS) has published a new index classifying thousands of species of plankton.

Today, two biologists from the CNRS are off on a fishing trip off the coast of Villefranche in southern France

“You’d think they were invisible but they are perfectly visible, they are small animals, one or two centimetres long, I can see a salp swimming around there,” says Christian Sardet, CNRS Research director and author of “Plancton: aux origines du vivant”.

The plankton they catch come to life under their microscope.

These strange-looking creatures sometimes have familiar traits and remind us of animals we know.

The newly published index includes a quarter of a million different species. Specialists say they believe the Earth’s seas and oceans contain about a million. Though many species are microscopic, plankton is made of organisms covering a wide range of sizes, including large ones such as jellyfish. They provide a crucial source of food to many large aquatic organisms, such as fish and whales.

The name plankton is derived from the Greek adjective “planktos”, meaning “errant”, and by extension “wanderer” or “drifter”. They live in the water column and typically flow with ocean currents.

Some are able to communicate, they even have neurons. Some have hearts that beat.

Among the species under study is the salp. Salps usually live as part of a community.

Their make-up is visible through their see-through barrel-shaped bodies. There is a central knot which contains the animal’s intestines. Salps swim through the water by the movement of hairlike fibres on their bodies or by pumping water through their bodies using their muscles. They may look primitive, but salps have a heart, gills and even something that looks like a placenta.

Close ancestors of vertebraes, they feed on phytoplankton and can grow at a rate which is probably faster than that of any other multicellular animal.

The salp reproduces asexually by producing a chain of tens to hundreds of individuals, which are released from the parent at a small size.

Scientists also took a close look at ctenophores or “comb jellies”. Their most distinctive feature is the “combs” or groups of cilia they use for swimming, and they are the largest animals that swim by means of cilia.

There are eight rows of combs, allowing the animal to move and rotate in three dimensions. Diffraction of light, from a flash for example, gives them a beautiful sheen.

Plankton represent 98 per cent of life in the ocean and play a vital role for human beings:

“When we breathe, with every other breath, we should thank plankton! Because half of the oxygen we breathe comes from plankton. The rest comes from plants and forests,” says Christian Sardet.

According to these scientists it’s high time we took more interest in this submarine world, threatened by human activity and vital for our survival.

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