By Mark Floyd, OSU News and Research Communications
“When all of a sudden the city air filled with snow,
the distinguishable flakes
looked like krill
fleeing the maw of an advancing whale.”
— Billy Collins, from Neither Snow
One of the most important animal species in the world lives in the frigid Southern Ocean, where individuals may reach a ripe old age of six or seven years, despite growing to a length of only 2 inches and not being able to swim against currents or tides to escape predators.
And the predators are many — from the largest animal to have ever lived on Earth, the blue whale, to Adélie penguins, seals and a host of seabirds. Of late, a new predator has emerged to this small, aquatic crustacean known as Euphasia superba — or Antarctic krill. It is humans, who are harvesting krill at an increasingly brisk rate as entrepreneurs have discovered lucrative markets for them as a nutritional supplement. Krill oil tablets, touted for their omega-3 oils and other health benefits, cost $20 to $30 for a small bottle.
Krill are so abundant, there historically have been few concerns about overharvesting them. In fact, if you put all of the Antarctic krill in the Southern Ocean on one side of a giant scale and the world’s 7.5 billion humans on the other side, the scale would tip in favor of the krill.
On the other hand, it wasn’t that long ago that people pointed to the iconic salmon in the Pacific Northwest and said it was a limitless resource.
Count Oregon State University marine ecologist Kim Bernard among those who are beginning to hear faint warning bells. It isn’t just an increase in human harvesting of krill — which also are used for aquaculture feed and pet food — that concerns the native of South Africa. It is what humans are doing to the planet that may be the biggest threat to the Antarctic krill, she says.
“For being as important as they are, there is a lot that we don’t know about Antarctic krill,” Bernard says. “We know that there are certain regions or ‘hot spots’ of phenomenal numbers of krill in the Southern Ocean, and no one had really known why. We also know that there is a correlation between abundant sea ice and healthy krill populations. Again, we’re not sure why.
“But we do know that warmer conditions along the West Antarctic Peninsula have resulted in reduced sea ice extent and duration and that is a major concern. It has had major ramifications across the entire pelagic (open ocean) food web in the region.”
Krill is a Norwegian word for ‘whale food’, and it fits this tiny shrimp for a good reason. Most baleen whales eat little else — and they can really pork out on krill. One study found that the gargantuan
blue whale, which can grow to the length of three school buses, eats as much as
4 tons of krill in a single day. In one mouthful, a blue whale can down half a million calories.
It’s easy then to see how an abundant krill population is important for cetaceans. They are not alone. Bernard’s own studies have found krill abundance, and convenience, is critical for Adélie penguins.
In a study funded by the National Science Foundation, the assistant professor in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences and her colleagues spent four consecutive summer seasons in the Antarctic mapping the patterns in distribution and biomass of Antarctic krill near Palmer Station, a known hot spot for the crustacean. They also sought to identify the environmental conditions responsible for the hot spot.
What they discovered is a near-perfect system in which krill aggregations situated over the Palm Deep Canyon, a region of nutrient-rich waters that produce a lot of food for krill, are delivered close to shore by tidal currents and winds. When the winds are westerly and the tides are diurnal — one high tide and one low tide each day — the krill biomass close to shore is at its peak, and krill aggregations are huge.
“It’s neat. We can predict exactly when humpback whales will be close to shore off Palmer Station just based on the tides,” Bernard says. “When there are diurnal tides, you’ll see krill from the surface to the ocean floor. They are everywhere. And when they are, the whales are there, too.
“This concentration and transport toward shore are particularly important for the penguins that breed there. The farther they have to go to forage, the less their chicks have to eat, and chick weight is a huge factor in their survival. A difference of a few hundred grams in chick weight is the difference between life and death.”
Bernard became interested in krill while working as a post-doctoral scientist on the Palmer Antarctica Long-Term Ecological Research project. She began studying the variability of their distribution and aggregation structure and looking at the relationship between krill and Adélie penguins.
The research, and the region, gripped her.
“Working in Antarctica is incredible. It’s hard to describe. I would spend all day out on a small, inflatable rubber boat with my field assistant, acoustically mapping krill. Some days would be bright and sunny, the ocean reflecting like a mirror. Penguins would ‘porpoise’ past us as we slowly motored along. Some days, we’d see humpback whales lunge-feeding on the krill. Other days were less calm and the wind can pick up very fast out there.
“I remember more than once when the winds picked up almost instantly, and waves of ice water were crashing over me as we raced back to Palmer Station, my hand gripping the tiller and staring straight ahead through snow- and ice-covered goggles as the frigid water stung my face. It was frightening, but honestly it was the most alive I’ve ever felt.”
Now Bernard is hoping to return to Palmer Station, this time in the winter, to see how Antarctic krill survives the frigid months, how oceanic conditions may differ, and most importantly, what role sea ice plays.
“We see very strong correlations between krill biomass and sea ice,” she noted. “When the sea ice is low, the krill populations crash the next summer. It could be a change in algae or other food for them, or it could be that sea ice provides shelter from predators, or affects the currents in some way. We just don’t yet know. But I’m hoping to find out.”