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Extreme Science: Is Ocean Acidity Harming the Copepods?

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By Ceri Lewis, Catlin Arctic Survey Ice Base scientist

This is the second in a series of blog posts from scientists taking part in the third-annual Catlin Arctic Survey.

I think copepods are cool. Not many people know about them, and I spent my flight to Ottawa introducing my colleagues in operations to the creatures that I’ll be spending my time in the High Arctic working on, and that I find so intriguing.

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

Copepods are crustaceans, and essential to the marine food chain. They eat algae, and may be sensitve to higher ocean acidity levels caused by an increase of carbon dioxide. Credit: Ceri Lewis/Catlin Arctic Survey.

The word copepod comes from two Greek words kope, meaning "oar", and pod, meaning "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 copepods in the world’s oceans. They would fill over 80 million Olympic swimming pools and weigh more than 16 billion double-decker buses. If you placed them end to end, they would stretch to the moon and back 87 million times.

There are nearly 200 billion more copepods than people on the planet, and even though they are small, their combined mass is over 400 times that of the human population. And at their fastest, they travel a hundred times faster than Usain Bolt. That’s 500 body lengths per second.

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 simple food like sugars. 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. They are also too small for the larger animals to eat efficiently.

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.

But copepods are sensitive creatures. They are susceptible to changes in the marine ecosystem. Increased levels of carbon dioxide (CO2) are being absorbed by the oceans, making them more acidic.

Using samples of Arctic sea ice, Lewis is studying how changing ocean acidity levels are affecting copepods. Credit: Ceri Lewis/Catlin Arctic Survey.

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 CO2 dissolved, the water acidified and reddened. This is now happening in our seas due to increased CO2 in our atmosphere, a process called ocean acidification, and it’s happening fastest in the Arctic Ocean.

My research on the Catlin Arctic Survey is to see how copepods respond to increased CO2 levels in the ocean. The results can help us to understand what will happen to Arctic marine food webs in the future, and has important implications for our fisheries.

When you think of Arctic wildlife, threatened ecosystems and climate change, the first thing that springs to mind for many people are polar bears. While they may look dramatic on a poster or in a documentary, copepods are the real stars of the show, and changes in their numbers could have drastic knock-on effects on the health of the marine ecosystem.

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