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Expedition Plankton - Think like a whale!

Posted on 03-10-2017 by Debbie Wall-Palmer

How to catch plankton - think like a whale!

The focus of our research during the AMT27 cruise will be mesozooplankton. ‘Meso’ means small (between 0.2 and 2 mm), ‘Zoo’ means animals and ‘Plankton’ are drifting organisms that cannot swim against a current. So we will be working on small drifting animals.

 ...but how do you find small drifting animals in the middle of the open ocean?

For this we take some inspiration from nature! We will use special nets that are the shape of a whale, with a wide mouth and a long body. Whales are a natural predator of plankton and have developed this shape to be efficient and expert plankton catchers. 

The opening or ‘mouth’ of the nets that we will use are 0.4 m2 to 1 m2. The larger the mouth, the more water is filtered for the plankton. And to make sure that we catch even the smallest mesozooplankton, the mesh of our nets is very fine, from 0.20 to 0.35 mm. The net funnels all of the plankton towards a collection chamber at the end, which is known as the ‘cod end’, where we can easily remove specimens without damaging them.

 ...but the open ocean is vast, how do you know where and when to cast your net?

For this, we must think like plankton, and begin to live like the plankton that we want to find! Many planktonic creatures undergo a diel vertical migration, which means they swim up from deeper water to near the ocean surface once every day, usually to feed. For the mesoplankton that we will study, this happens during the nighttime, when predators at the ocean surface, such as fish, are less able to see. This means that we must wake up very early in the morning, between midnight and 4 am so we can cast our nets in the surface waters and collect the best plankton. Our day becomes shifted while we are working on the ship so we work when the plankton are active and sleep when the plankton are resting!

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