Getting to the Heart of the Matter

Everyone is worried about the impacts of continued warming in the Arctic on polar bears. But who’s looking out for the copepod?

That’s right, the copepod. OK, they don’t have big brown eyes. But they do have one really tiny brown eye-ish thing right in the middle of their otherwise unremarkable little heads. They weigh about 8,000 times less than a polar bear but copepods have far greater influence over the health of the Arctic ecosystem than that charismatic fuzzy white mammal.

Copepods are tiny crustaceans—relatives of shrimps and crabs—that occur in great numbers in the oceans. A few species live the Arctic Ocean. These copepods play a crucial role in a relatively short but important food chain. They are half-inch swimming energy packets. Their role is to eat loads of tiny plant-like algae, each one adding a bit more energy to their battery, then transfer all that stored energy to the animal that eats them. That animal, in turn, becomes someone else’s prey and so on. Who else is in that food chain? Fish and whales eat copepods, seals eat fish, polar bears eat seals and people eat polar bears and whales. That’s a bit simplified, but this is a blog not a biology class.

So if copepods are so important to the Arctic food chain, what will happen to them if temperatures, pH and oxygen levels continue to change in the Arctic Ocean?

Like so much about the Arctic, nobody knows. But rest easy fellow copepod fans, Helen Drost is on the case. Helen is a PhD student who’s working with Tony Farrell at the University of British Columbia and Eddy Carmack at Fisheries and Oceans Canada. She wants to know what impacts the temperature, pH and oxygen level changes in the Arctic are likely to have on copepods and the Arctic cod that eat them.

Dr. Farrell has done some interesting work looking at how temperature affects heart rate in animals such as salmon. Heart rate is a pretty good indicator of physiological stress, and just like us, their hearts can only beat so fast before things start to go wrong.

So a logical question is, if it works with one species of fish could it work with a tiny little copepod?

It looks like the answer is yes. Helen has tested the system with a local crustacean called Daphnia. Like some fish, Daphnia’s little heart keeps beating faster as the temperature increases until it succumbs to a crustacean version of a heart attack.

Helen is now ready to collect copepods and Arctic cod from Resolute (Cornwallis Island) and Cambridge Bay (Victoria Island) and run the experiments on them. It will be a while before we know what the Arctic copepods can handle but it’s an important question. The changes are already underway in the Arctic Ocean. Arctic copepods will either adapt and survive the changes, change their distribution or disappear altogether.

The fate of all the other animals in that food chain may very well depend on the beat of one of the smallest hearts on the planet.

Watch a video of Daphnia heartbeat. This was taken with Daphnia in cooler water and the heartbeat is slower than normal. Video courtesy of Helen Drost.