On Copepods (Arctic Blog)

Ceri thinks copepods are cool. I didn’t know what a copepod was. I hadn’t even heard of them before I met Ceri.

We met at Heathrow airport on the way to join the Catlin Arctic Survey and compared choices of bad films on the flight to Ottawa.

Dr Ceri Lewis of the University of Exeter drew a picture of a copepod for me on the paper table cloth of Montana’s in pink crayon. It looked like an elongated marine wood louse.

A copepod is a small marine animal. It is a crustacean, which means it is related to lobsters, shrimps and crabs. Copepods are plankton, animals (zooplankton) and plants (phytoplankton) that are carried by ocean currents rather than making their own way in the world.

The word copepod comes from two Greek words kope- oar and pod- foot. These are the oar-footed creatures and they are the most abundant animal on this planet.

There are an estimated 1,347,000,000,000,000,000,000[1] copepods in the world’s oceans.

They would fill over 80 million Olympic swimming pools[2] and weigh more than 16 billion double-decker buses[3].

If you placed them end to end, they would stretch to the moon and back 87 million times[4].

There are nearly 200 billion times as many copepods than people on the planet, and even though they are small, their combined mass is over 400 times that of the human population[5].

At their fastest, they travel a hundred times faster than Usain Bolt[6]. “My little babies rock,” Ceri reminds me.

Not only are there a lot of them, they are also essential for the marine food chain. In any food chain there are the ‘primary producers’, life forms that take energy from the sun and turn it into carbohydrates, simple food. In the seas, this is algae, which are anything from single-celled phytoplankton to hundred foot long kelps and meadows of sea grass. This marine plant life does not generally contain the more complex carbohydrates, fats and proteins needed to sustain larger animals.

Copepods are secondary producers, gobbling algae gathered by their front three pairs of legs, and turning this into the more complex building blocks needed for larger marine life. They feed at night, avoiding their natural predators of krill, fish and baleen whales. During the day they can tail-flick as much as 500 metres down out of sight: a journey equivalent to you or I travelling from John O’Groats to Lands End on a daily basis, a 1,400 mile round trip.

But copepods are sensitive creatures. They are susceptible to changes in the marine ecosystem. Increased levels of carbon dioxide are being absorbed by the oceans, making them more acid. Do you remember this experiment when you were at school? You had to blow through a straw, bubbling a beaker of water containing a pH (acid level) indicator. As your exhaled carbon dioxide dissolved, the water acidified and reddened. This is happening in our seas and nowhere faster than in the Arctic Ocean.

Ceri’s work over the next three and a bit weeks is to see how copepods respond to increased acid levels in the ocean. The results can help us to understand whether fish and chips may be the caviar of the 21st Century.

When you think of Arctic wildlife, threatened ecosystems and climate change, you think of polar bears. At least I did. They look better on a poster or in a documentary, but copepods are the stars of this show and changes in their numbers could have drastic knock-on effects on the health of the marine ecosystem.

To learn more about the Catlin Arctic Survey visit:

[1] Estimate taken from GA Boxshall –
[2] Estimate of ocean volume from GA Boxshall multiplied by 0.1455ml/m3 global average displacement volume – from COPEPOD: A Global Plankton Database 2005 The minimum volume for an Olympic swimming pool is 2,500 m3, but can be more.
[3] Estimate of ocean volume from GA Boxshall multiplied by 177.3mg/m3 global average wet mass – from COPEPOD: A Global Plankton Database 2005 The weight of an unladen double-decker bus is 14,560kg.
[4] Dr Ceri Lewis over a coffee in South Camp Inn, Resolute Bay reckons that 0.5mm is a good working length for a copepod. Someone else measured the distance from the earth to the moon.
[5] Estimates used are a human population of 6.91 billion and an average weight of 60kg.
[6] Strickler 1977 estimates a copepod’s escape speed at 500 body lengths a second. This comparison assumes that Usain Bolt is exactly 2 metres tall and runs the 100 metres in 10 seconds.

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