Wednesday, November 16, 2011


Figure 1. Changes in krill and salp densities over time: a) Krill density in the SW Atlantic sector; b) post-1976 krill density in scientific trawls; c) 1926–2003 circumpolar salp data. Figures from Atkinson et al. (2004)
We might ask ourselves this question on a day like today, when the winds have sprung back up, whipped up the waves, thrown ice bergs in our path, caused the ship to pitch and roll ceaselessly, and stopped us from carrying out the sampling we had planned for today. But in fact, this question – in a larger context – is important to many of us who have spent much of our lives studying the ocean, especially the Southern Ocean. 

We are here in the Western Antarctic Peninsula (WAP) region of the Southern Ocean because it is a bell-weather region for climate change and global warming. A 2004 paper by Angus Atkinson and others summed it up well:  

“The western Antarctic Peninsula is one of the world’s fastest warming areas, and (atypically for the Southern Ocean) winter sea ice duration in this sector is shortening. Key spawning and nursery areas of krill are thus located in a region that is sensitive to environmental change. Deep ocean temperatures have increased, and a circumpolar, pre-1970s decrease in sea ice has been indicated at several locations. The regional decrease in a high-latitude species with high food requirements (krill) coincides with an increase in a lower-latitude group with lower food requirements (salps). However, as the mechanisms underlying these changes are uncertain, future predictions must be cautious. These changes among key species have profound implications for the Southern Ocean food web. Penguins, albatrosses, seals and whales have wide foraging ranges but are prone to krill shortage.”

Figure 2. Southern Ocean food web. Image British Antarctic Survey
The vulnerability to climate change of the Southern Ocean pelagic ecosystem – and the special
Figure 3. Top: The Southern Ocean krill, Euphausia superba (Photo Uwe Kils). Center and bottom: The Southern Ocean salp, Salpa thompsoni, solitary and aggregate forms (Photos Larry Madin, WHOI)
vulnerability of krill - is of deep concern to oceanographers and climate scientists. Krill are a keystone species for this ecosystem, meaning they are pivotal to the nexus of relationships among species that live here and are connected in a “who-eats-who” framework, known as a food web. The Southern Ocean food is pretty simple compared to many other ocean regions. There are fewer species and fewer trophic steps to the top predators or “charismatic megafauna” (seals, whales and porpoises) that many people know and love best. This cruise is focused on salps and krill, and our goal is to help ensure that many people know and love these creatures best – or at least as much – too. To help make our case, here are the major protagonists of our story, alive and well and looking their charismatic best (Fig. 3).

-- Ann Bucklin (University of Connecticut)

Citation for quotation:

Angus Atkinson, Volker Siegel, Evgeny Pakhomov & Peter Rothery (2004) Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432: 100-103

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