When it comes to Antarctic wildlife, penguins, seals and whales grab all the attention but there is one species that visitors are unlikely to see but without whom the entire ecosystem would be vastly different. To celebrate World Krill Day on August 11 we spoke to krill biologist Dr Kim Bernard, who is currently over-wintering at Palmer Station on the Western Antarctic Peninsula, to learn more about these creatures that are at the heart of the Antarctic food web.
Researching in Antarctica
You’re a real Antarctic veteran, but how did you become interested in krill?
In total, I’ve spent nearly 38 months at Palmer Station – five 5 summer seasons, and I’m currently in my third winter season here. I’ve also spent around 60 weeks at sea in the Southern Ocean aboard various research vessels. My earliest research cruise was back in 2000 and my most recent was this year aboard the RV Laurence M. Gould along the Antarctic Peninsula.
It was on the first of those cruises that I worked with Antarctic krill for the very first time! I instantly fell for them with their big eyes looking up at me from the bucket of seawater, and the rest, as they say, is history.
Your social media handle is even @Psychokriller!
It sure is. Psycho Kriller used to be my radio name at Palmer in the summers when my research assistants and I would spend hours each day out in a small Zodiac acoustically mapping krill. I always found the Talking Heads song fun and especially loved the krill pun, so the name just stuck.
The importance of krill
So what exactly are krill?
Krill (also known as euphausiids) are small crustaceans similar to shrimps but in an entirely separate order known as Euphausiacea. There are over 85 species of krill throughout the world’s oceans, from the Arctic to the Antarctic and everywhere in between. Some species live in the surface waters of the ocean, while others live at great depths. The word ‘krill’ comes from the Norwegian for ‘small fry fish’ – this name was probably given to krill because they swarm and are an important food item for larger fish, marine mammals, seabirds and other top predators, much like fry fish are.
The name Euphausiid comes from the Greek ‘eu’ for good and ‘phausis for shine or illuminating because of krill’s bioluminescence. Krill have ten sets of light emitting organs called photophores and when they are disturbed or stressed they emit a brilliant blue light. There’s so much more to say about krill, but I’ll stop here!
Why are krill so important to the Antarctic ecosystem?
There are several species of krill in the Antarctic, but I’ll focus specifically on Antarctic krill (Euphausia superba) because it is by far the most abundant species here. Actually, it’s considered to have the greatest biomass of any non-domestic animal on Earth, with an estimated biomass of 500 million metric tons.
Antarctic krill are a fundamental part of the marine food web here and provide an important link between the base of the pelagic food web (phytoplankton, but more specifically, diatoms) and top predators, including baleen whales, various seals, penguins, many different seabirds, as well as fish and squid. Some of these animals eat krill exclusively, while apex predators like orcas eat other animals that directly feed on krill. It’s the vast numbers of Antarctic krill that allow all of these top predators to thrive. Without krill Antarctica really wouldn’t be the same. For example, when Adélie penguin chicks are growing, they depend heavily on getting enough krill in their diet before they fledge. If they don’t get enough, they fledge underweight and there is a greater chance of them dying during the winter.
Is it true that krill also have an important role to play in the carbon cycle, removing carbon from the atmosphere?
The diatoms (microscopic algae, or phytoplankton) that are an important part of the diet of krill take up carbon dioxide in the surface waters of the ocean through the process of photosynthesis. That CO2 diffuses into the surface waters from the atmosphere. The diatoms accumulate the carbon, using it to fuel growth and reproduction. When krill consume diatoms, they take up that carbon and use it to fuel their own growth and reproduction. Some of the carbon they eat is discarded in the form of faecal pellets, which sink quickly to the seafloor. Some of that carbon is remineralized by bacteria and released, but a large percentage of it will reach the seafloor. Once the pellets reach the floor, the carbon in them is trapped and unlikely to reach the sea surface and the atmosphere for thousands of years. In this way, Antarctic krill contribute to the carbon sink in the Southern Ocean. Their sheer numbers mean that the amount of carbon they send to the seafloor is massive: equal to the amount of carbon emitted by 2 million school buses each year.
Understanding krill life cycles
Can you explain what your current research is about?
I currently have two active National Science Foundation-funded krill projects, but the one that has brought me down for my third winter at Palmer Station is called ‘The Omnivore’s Dilemma: The effect of autumn diet on winter physiology and condition of juvenile Antarctic krill’. The food available along the Antarctic Peninsula is changing in response to climate change so it’s very important to know if the type of food available affects the health of krill.
Why a dilemma? Well, in addition to diatoms the krill also eat small zooplankton like copepods. Winter in Antarctica is characterised by darkness and low food availability and krill have different strategies to survive this. We have a good idea of the strategies that adult and larval stages of Antarctic krill use to survive the winter, but there has been a huge gap in our knowledge about juveniles. Do they lower their physiological processes and limit food intake like adults? Or do they need to keep feeding like larvae? Can they find enough food and, most importantly, is the type of food – phytoplankton or zooplankton – important?
What have you discovered?
Over three winters at Palmer Station, my team and I have made some surprising findings. Firstly, if juvenile krill find food, they’ll eat it. Those that only eat diatoms have fewer body fats, which is a metric for health and condition. Instead, they have to eat small animals like copepods to maintain their health and condition through the winter. But juvenile krill that only eat copepods in the winter will shrink, whereas those that eat diatoms will grow. Ultimately, we found that juvenile krill do best when they have an omnivorous diet.
Why is this important?
The problem is that with warming along the Antarctic Peninsula, diatoms are becoming less abundant and copepods are becoming more abundant. So, there is a shift in the types of food available to krill and this could have a huge impact on their overall health and physiology and the success of the population.
Threats to the Antarctic ecoysytem
Industrial krill fishing is also on the increase in the Southern Ocean. As well as climate change, should we be worried about overexploitation of krill?
I should start by stating that the percent of the krill population that is fished each year is low. However, I think we should be very worried about overexploitation because humans have a tendency to do that.
The fishery is currently harvesting krill well into the winter months. There’s no seasonal closure on the fishery, perhaps because in the past the presence of sea ice in the winter would limit access to prime fishing grounds. Antarctic krill at the Western Antarctic Peninsula move inshore in the wintertime where they accumulate in vast numbers in the coastal straits, bays and fjords. This is exactly where the fishery is now targeting. So although they are only removing a small percentage of what we think is the total krill population, they are heavily fishing this relatively small area that is incredibly important not only for wintering krill, but also for the numerous top predators that rely on krill to sustain them through the winter months, many of which do not migrate elsewhere.
Proposals have been put forward to establish a Marine Protected Area along the Western Antarctic Peninsula. This would be critical to preventing overexploitation, ensuring the sustainability of the Antarctic krill population, and preserving resources for higher trophic level populations. However, this requires full international consensus in order to approve these measures and this hasn’t yet been achieved. I worry that the demand for krill-related products (particularly omega oil supplements) is going to keep increasing, putting pressure on the fishery to grow even faster. With the global political instability we see these days, it worries me that it might not be possible to control fishing efforts in the Southern Ocean. We see a huge amount of illegal fishing globally, I worry that this could become a problem in the Southern Ocean too. I worry a lot about these things, as you can probably tell.
Read more about Dr Bernard’s work at the Zooplankton Ecology Lab.
Swoop Antarctica can’t promise you krill, but we’ve got the penguins, seals and whales covered. Learn more about Antarctic wildlife here.