Posted on behalf of Jane Qiu
Science journalist Jane Qiu is at the Palmer ecological research station on the Antarctic Peninsula, joining researchers investigating how climate change has affected the region in recent decades. Please check back for her dispatches from the bottom of the world.
Kim Bernard and Carolina Funkey, ecologists of the Virginia Institute of Marine Science in Gloucester Point, fondly known as the krillers at the Palmer ecological research station in western Antarctic Peninsula, are out fishing again. They have been towing nets repeatedly within the three-kilometre boating range around the station, in the hope of catching enough Antarctic krills – shrimp-like creatures and a key food source for most predators in the Antarctic – to study their dietary preferences.
I accompany the krillers on their fishing trip through the cobalt-blue water of the Southern Ocean in an inflatable boat named “psychokrillers”. When we get to Station E, a patch of water on the southern edge of the boating limit, the researchers lower the net – essentially a meshed cylinder roughly one metre in diameter and three metres long with a bottle connected to the far end.
The krillers wait till the bottom of the net sinks to around 20 metres below the surface, with the opening roped up to the end of the boat. Guided by the Global Positioning Satellite, Bernard steers slowly and steadily to the north. A couple of penguins swim by, which Jennifer Brum, a virologist of the University of Arizona in Tucson, notes down in the lab book. “Such observations will help us locate areas that have krills,” she says.
Twenty minutes later, having towed for about one kilometres, Bernard swings the boat around while her team members pull the net from the water. They detach the collecting bottle from the net and pour the content into a container and repeat the towing process. We get about 50 krill in total. “This is about the average,” says Bernard. “We don’t seem to be getting a lot of krills here.”
This is probably not surprising as recent studies show that krill abundance in waters that border the South Ocean and southwestern Atlantic Ocean, including those around the western Antarctic Peninsula – which contain over half of the Antarctic krill stock – has declined by nearly 40% since 1976. This is correlated with a decline in the extent of sea-ice and of microscopic plants called phytoplankton, the starting point of the food chain.
The ice season, which has shortened by 90 days in the past 50 years, is having multiple effects on the abundance of krill , says Bernard. The decline in sea ice causes the water to mix more deeply, thereby reducing the photosynthetic activity of phytoplankton. Meanwhile, sea ice is crucial for the survival of krill larvae: it protects them from their predators, and ice algae are a key food source for larvae in winter.
Indeed, early on this year, on the annual cruise of the Palmer Long-term Ecological Research (LTER) programme – which was set up by the US National Science Foundation twenty years ago to study the effects of environmental changes – Bernard and her colleagues found that krills were not eating enough phytoplankton to meet their metabolic demand.
With their favourite food dwindling, krills “may be forced to find other food sources”, says Bernard. To find out what those new food sources are and what the implications are for other components of the food chain, the krillers will grow different numbers of krill in sea water in the laboratory and measure the changes in the amount of phytoplankton and tiny marine animals called micro-zooplankton.
In this year’s research cruise, which will kick off early next month, the team will be doing similar experiments along the peninsula between Palmer and Charcot Island 700 kilometres to the south. “This will give us a better idea of krill distribution and diet preference in a much larger area,” says Bernard.
Probing ocean acidification
Image: Kim Bernard reads a flowmeter as Carolina Funkey holds the net/ Jane Qiu