This is a discussion of the recently published study, Oil exposure in a warmer Arctic: Potential impacts on key zooplankton species. An abridged version can be found here.
A new study published in the latest edition of the journal Marine Biologyasks what impacts the warming ocean and oil extraction activities might have on one of the most significant types of plankton in Arctic seas: small relatives of shrimp called copepods. The study is a strong example of how little we still know about Arctic marine systems at a time when pressure is growing to extract oil and gas, develop new fisheries, increase shipping traffic and other activities.
Here’s the context:
We’ve talked about copepods in the past and won’t repeat ourselves here except to say that copepods are the critical link between plants and a significant portion of the rest of the Arctic marine food chain. Tiny floating single-celled algae make a living by capturing energy from the sun and storing it in their cells. All animals need that energy in order to survive, but only a few critical animals like the copepods are capable of accessing it directly by eating the algae. They get more energy than they need on a daily basis and store it mostly in the form of lipids (think fat). If they ever find themselves in a tight situation for food, they’ll draw on those lipids for energy. More likely, though, they’ll get eaten and those lipids will serve as energy for whoever eats the copepod.
So copepods are like little batteries that store energy in their lipids. Fish, birds and even several whale species get their energy by eating the copepods.
But not all copepods are created equal; some species have more lipids than others. That means that some species are more energy-rich than others.
Copepods also vary in where they occur. Areas where a lot of high-energy copepods occur can support more animals up the food chain; areas with lower-energy copepods can’t support as much. In many Arctic regions, the dominant copepods are energy-rich and support an abundance of life.
As the climate patterns around the world change, the distribution of plants and animals is also beginning to change. And if the distribution of these species of copepods changes, there could be consequences all the way up the food chain.
Which brings us to this study
The paper describes experiments run by Morten Hjorth and Torkel Gissel Nielsen from Aarhus University and Technical University, respectively, in Denmark. They are interested in how temperature changes and the potential for oil in the environment could affect two competing species of copepod, one energy-rich and one less nutritious.
Calanus glacialis is found only in Arctic waters. It’s got a lot of lipids, so it’s a good high-energy food. It supplies much of the energy needed to support the biomass and diversity found in the Arctic marine environment.*
Calanus finmarchicus is found mostly a bit further south but extends up along the coast of Greenland as well. Compared to C. glacialis, this one is junk food: it’s got less than a quarter of the lipids and provides less energy for whoever eats it.
As Arctic temperatures increase, the more southern, less nutritious copepod (C. finmarchicus) could start to take over in the North and outcompete the other. To further complicate the issue, previous studies have suggested that the amount of lipids a copepod caries around may also have some impact on how sensitive it is to oil in the environment. So the dynamic between the two species could also be changed if oil if oil is added to the mix.
The researchers collected both species of copepods off the coast of Western Greenland and set up an experiment that varied temperature and exposure to a chemical called pyrene which represents oil-related pollution. They used faecal production and egg production as proxies for health; how much they poop is an indicator of how much they’re eating (remember, they eat microscopic algal cells so counting how many they eat isn’t really an option), and egg production is a measure of overall reproductive capability.
What they found
These are tough questions that won’t be answered in a single experiment. There remains much more work to be done before much can be said conclusively. So if you’re looking for the Big Discovery that answers all our questions, prepare for disappointment. But the study does point us in certain directions and helps to inform important dialogues about the North.
The basic findings were that C. finmarchicus (the southern, low energy copepod) is likely to do better than C. glacialis as temperatures increase in the North. If that’s the case, we could expect this lower energy copepod to become the dominant species in the North. Given that it is a poorer source of energy, the increase in its abundance would be akin to flooding the market with cheap junk food and could have significant effects on the rest of the food chain. Less available energy means that the food chain could not support the amount of life that currently defines the Arctic food web.
But the real world, of course, is much more complicated than that. Among those complications: we’re currently contemplating a range of new activities in the North that could introduce oil into the equation.
Based on these experiments, the less energy-rich copepod that may prevail in a warmer Arctic is more sensitive to oil. So what does that mean?
To quote nearly every scientist at one point or another, “well it depends”.
Putting it together, it could look something like this:
Warmer water replaces much of the energy-rich copepods with junk food copepods. Less life can be supported as a result of lower amounts of energy available to the food chain. But these now dominant copepods are more vulnerable to impacts from oil spills. In the event of a spill, an already weak energy source would be further reduced.
There is, however, the possibility that in the presence of oil, C. glacialis (our high-energy copepod that is less sensitive to oil) might end up with the advantage, even in warmer waters. The authors suggest that “. . . the less sensitive C. glacialis may do better in an oil-polluted warmer future”. Either way, we’d still have fewer copepods around than we do now.
You may be thinking, then, that the key to making it a fair fight between the two copepods in a warmer Arctic is actually to add oil. And therein lies the danger of reading too much into ongoing scientific studies. These researchers are years away from understanding the system in question, let alone suggesting that we do anything about it, except maybe to try and slow global warming.
So what does this mean for the rest of us?
Probably the most important message is that we still understand very little about Arctic marine systems and how the changes that are now occurring may impact them. But we understand them enough to know that there will be impacts; and we know the nature of those impacts will be complex and depend on many factors.
Meanwhile, we have many decisions to make—about oil and gas extraction, shipping traffic and wildlife management to name a few. The pressure to make these kinds of decisions is increasing and the bottom line is that we don’t yet have a lot of good solid information with which to make them. Are we even prepared to make these decisions at all based on the information at hand? While the race for better scientific understanding continues, perhaps the biggest question in front of us is just what kind of decisions we are willing to make in the face of so many uncertainties.
If you’d like to read the report (and are willing to get past the paywall), here’s the study:
Hjorth, M. & Nielsen, T. G. (2011). Oil exposure in a warmer Arctic: Potential impacts on key zooplankton species. Marine Biology