Antarctic Krill Provide Carbon Sink In Southern Ocean

Scientists from British Antarctic Survey (BAS) and Scarborough Centre of Coastal Studies at the University of Hull discovered that rather than doing so once per 24 hours, Antarctic krill 'parachute' from the ocean surface to deeper layers several times during the night. In the process they inject more carbon into the deep sea when they excrete their waste than had previously been understood.

Lead Author Dr Geraint Tarling from BAS says, "We've known for a long time that krill are the main food source for whales, penguins and seals, but we had no idea that their tactics to avoid being eaten could have such added benefits to the environment. By parachuting down they transport carbon which sinks ultimately to the ocean floor -- an amount equivalent to the annual emissions of 35 million cars -- and this makes these tiny animals much more important than we thought."

Krill feed on phytoplankton near the ocean surface at night but sink deeper in the water column during the day to hide from predators. By knowing how these animals behave, we can understand better the contribution they make to removing carbon from the Earth's atmosphere and upper ocean.

Background

Satiation gives krill that sinking feeling by Geraint A. Tarling and Magnus L. Johnson is published in Current Biology on 7 February 2006.

Antarctic krill (Euphausia superba), are shrimp-like crustaceans that are one of the most important animals in the Southern Ocean. They feed on phytoplankton and are in turn eaten by a wide range of animals including fish, penguins, seals and whales. Phytoplankon are the starting point for the marine food chain and use photosynthesis to extract carbon from carbon dioxide.

Krill live in the open ocean, mainly in large swarms and reach particularly high numbers in Antarctica. The migrations that they perform (called Diel Vertical Migrations, DVM) are a way of transporting carbon to the ocean's interior because they eat phytoplankton at the surface and excrete their waste at depth. Antarctic krill can grow up to a length of 6cm and can live for 5-6 years. They are one of the largest protein resources on Earth and can be fished easily with large nets for human consumption.

There is enough Antarctic krill to fill the total volume of the new Wembley stadium 1500 times. Spread out on the floor, they would cover the entire area of Scotland. The total weight of Antarctic krill is calculated between 50-150 million tonnes.

The krill migrate from the ocean surface by fanning out their swimming legs and enter a controlled descent, akin to parachuting. The behaviour is most apparent when their stomachs are full and may be an effective means of getting out of harms way when they can eat no more.

Numbers of Antarctic krill have dropped by about 80% since the 1970's. The most likely explanation is a dramatic decline in winter sea-ice. Krill feed on the algae found under the surface of the sea-ice, which acts as a kind of 'nursery'. The Antarctic Peninsula, a key breeding ground for the krill, has warmed by 2.5°C in the last 50 years, with a striking decrease in sea-ice. It is not fully understood how the loss of sea-ice there is connected to the warming, but could be behind the decline in krill.

The study was carried out aboard the British Antarctic Survey ship RRS James Clark Ross from December 2004 - January 2005 around the islands of South Georgia in the South Atlantic. The krill were caught with nets and transferred to tanks for observations. The tanks were continuously supplied with water (and therefore food) from the sea surface.

British Antarctic Survey is a world leader in research into global issues in an Antarctic context. It is the UK's national operator and is a component of the Natural Environment Research Council. It has an annual budget of around £40 million, runs nine research programmes and operates five research stations, two Royal Research Ships and five aircraft in and around Antarctica. More information about the work of the Survey can be found at: www.antarctica.ac.uk

Centre for Coastal studies is based at the Scarborough campus, at the University of Hull. The Centre for Coastal Studies is a small but vibrant centre, specialising in teaching and research with a strong emphasis on fieldwork. The centre attracts around 50 students a year from a wide range of backgrounds who study degrees in Coastal Marine Biology, Environmental Science and Ecology. Students acquire strong theoretical knowledge of their subject combined with skill and expertise in the field. Academics and postgraduates in the centre are currently working on a diverse range of topics including intertidal ecology, krill morphometrics, fisheries management and tropical fish biology. For more information visit: www.ccs.hull.ac.uk