• 4 Jan 2016

Secret life of plankton

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Feast your eyes on this gorgeous spread of plankton because most of these wandering species are usually invisible, and until now, were unknown to science. That changed in May, when Science magazine published a study of the samples collected by the schooner Tara Explorer on its four-year global voyage. It revealed a treasure trove of new species ranging in size from viruses to centimetre-sized crustaceans. Chris Bowler, a member of the research team, told the BBC: “There are about 11,000 formally described species of plankton – we have evidence for at least 10 times more than that.” Plankton, from the Greek word for wanderer, may be microscopic, but their influence on the planet is huge. Collectively they generate 50% of the planet’s oxygen.

Credit: Christian Sardet

Soft clouds...

It looks like an exploding galaxy. It’s actually a radiolarian Thalassolampe margarodes, less than a centimetre wide, caught off the French Mediterranean coast. The yellow centre houses the cellular machinery. The fluffy white material around it stores nutrients and controls buoyancy. Its surrounding galaxy of jelly is dotted with hundreds of photosynthetic microalgae that trade oxygen and sugar in return for their board and keep.

Credit: Christian Sardet / Noe Sardet

...and toxic daggers

The needle-sharp Pseudo-nitzschia are diatoms, a type of algae. The pointy shape lets them glide effortlessly through water, but they also produce a toxin called domoic acid. The nerve-damaging poison can accumulate up the food chain, causing food poisoning and brain damage in sea lions and even humans.

Credit: NCMA Sample collection, Bigelow laboratory Booth Bay USA

Armoured inside...

This square-shaped cell, also caught off the Mediterranean French coast, is Lithoptera fenestrate, a prey-capturing acantharian less than a millimetre across. Our skeleton is built from calcium but L. fenestrate uses strontium ions in seawater to build a tough internal cross frame – the only known marine organism able to commandeer strontium for this purpose. The solid scaffold makes an attractive home for symbiotic photosynthesising microalgae (yellow spheres).

Credit: John decelle / Fabrice not

...and out

Dinoflagellate hunters such as this single-celled Protoperidinium, prefer armour on their exterior to avoid being eaten themselves. Their delicately patterned shells called “thecas” are made of cellulose – the same fibre that gives wood its strength.

Credit: PHILIPPE CRASSOUS / getty images

Ethereal smoke...

The fragile jellyfish Hippopodius hippopus, which grows up to five centimetres, drifts through the ocean like little puffs of smoke. Their flower-like “swimming bells” are clear as glass most of the time, letting this jellyfish slink past predators or toward prey unnoticed. It flashes opaque white when touched – perhaps as a warning to fish that come too close.

Credit: Stefan Siebert / Brown University USA.

...and Samba queens

The larvae of cephalopods – the group that includes octopus and squid – are known as chameleons of the sea, and it’s not hard to see why. Planctoteuthis larvae, around a centimetre long, flash their red and yellow pigment cells to communicate with other larvae, or as a defence mechanism – making them look big and fierce to predators.

Credit: Karen Osborn / Smithsonian Museum of Natural History Washington DC

Immortality...

The mesmerising medusa Oceania armata – a centimetre-wide jellyfish – may live forever. Its close cousin, Turritopsis dohrnii, has mastered immortality. When O. armata reaches adulthood, as shown here, it transforms from a free-swimming medusa back into a ball of cells that revert to an earlier stage in the lifecycle: a tethered branching polyp that eventually buds off genetically identical medusas.

Credit: David luquet / observatoire oceanologique de villefranche-sur-mer.

...and the fast life

Stephanopyxis palmeriana diatoms have no such patience. Under the microscope, these single-celled photosynthetic algae, thinner than human hair, look like strings of jewels. Up to a million cells long, they can be spawned by a single mother cell in three weeks.  But these jewels don’t last. With each generation, the cells shrink. Once it reaches a critical size, a diatom will cast off its shell and spawn a big new parent cell to start the lifecycle afresh. 

Credit: ncma collection / bigelow laboratory

Photos from Plankton: Wonders of the drifting world By Christian Sardet, University of Chicago Press (2015)

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