Copepods and the food web

Say hello to my little friend

 

Calanus

zooplanktonCopepod meet reader. Reader meet copepod. Congratulations, you’ve just been introduced to one of the most (if not the most) important animals in the Arctic Ocean. I’m here in the Fram Strait trying to understand how the feeding ecologies of the dominant three species of zooplankton, Calanus finmarchicus and Calanus glacialis (which are rather hard to tell apart), and their much larger sister Calanus hyperboreus are changing as a result of climate change.

These tiny species (fully grown adults are just 1 – 5mm long) are vital for the arctic ecosystem. Calanus have several impressive talents that make them an ideal food source for other animals, such as fish and even whales (it’s hard to believe how such a small animal could feed something as big as a whale, but through sheer quantity and national value of Calanus, it’s easy to see why whales choose them).  They store large amount of fats in their bodies, which they then use to fuel both their 8-month long winter hibernation period (that we call diapause) and their reproduction once they wake up and resurface in the arctic spring. Also, when it sinks down through the water even their poo sustains the feeding of organisms that live at great depths or on the sea floor!

areaNot only are they important for the arctic food web, they are also important for our understanding of the impact of climate change on the arctic ocean. See, C. finmarchicus is well known to be associated with the North Atlantic, C. glacialis with shallow arctic shelf seas, and C. hyperboreus feels most at home in the deeper oceans of the Arctic. So, for example, if we find that C. finmarchicus are becoming more numerous in the high arctic, we can assume that more North Atlantic Water is intruding into the arctic – which indicates that the arctic is warming up. What they eat can also inform us on just where the all the energy and nutrients come from that end up in the food web, and if this too is being altered by the changing arctic.

So just what am I doing about it? Good question. I’m here to specifically research how their feeding patterns have changed, both over time and space. Whether all this melting ice and warmer water is changing what they feed on. If I detect these changes, then it is direct evidence that warming in the arctic has direct impacts on the food web. But how do you do this? How do you analyse the diet of something so tiny? Two good questions.

Firstly, I find a ship and get on it. Hopefully it’s going to the Arctic.

bongosSecondly, I place a bongo  net down to 200m below the ocean’s surface and drag it back up to capture as many Calanus critters as I can.

Thirdly, I take these into the onboard lab (while trying not to get distracted by the electric blue luminescence of other zooplankton) and pick these out under a microscope and pack them into small tubes to be frozen at -80˚C!

Fourthly, once I’m back on land I’ll analyse the amounts of the different types of nitrogen and carbon that the Calanus are made up of (we call these isotope ratios if you want to learn more).

Fifthly, because the nitrogen and carbon types in the Calanus are similar to those found in their food, I then estimate which food source they are feeding on. So, if Calanus are feeding on algae that grows in the ice and is released into the surface water when it melts, their nitrogen and carbon ‘signatures’ will be similar to that of the ice algae.

Lastly, I present my work and I collect my Nobel Prize.  There is no Nobel Prize for ecology – but a man can dream.

 

Thanks for reading, here’s a polar bear.

polar bear winking

 

 

–  Elliott Price

 

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