The PAL study region along the western Antarctic Peninsula is one of the most rapidly warming places on the planet (see bullet 2), and the ecosystem is responding to the rapid climate warming. PAL observations of the Antarctic marine foodweb started in 1990, but some changes are just now becoming apparent. Antarctic foodchains are traditionally believed to be short and simple, efficiently funneling energy to large predators like seals and whales. We believe we’re witnessing the development of a much more complicated foodweb with new types of grazers and increased microbial activity (Figure 1).
A large decline in the local Adèlie penguin population was apparent by the late 1990s (see bullet 3). Detecting change in penguins is relatively straightforward because their colonies are at fixed locations and the birds’ behavior is predictable. Changes in other species are more complicated, often masked by large annual variations that make the longer-term trends hard to spot. For example, we documented a change in the phytoplankton (the “producers” at the base of the marine foodweb) along the Antarctic Peninsula, but it took 30 years of satellite data to nail it down (Montes-Hugo et al. 2009).
Another case is even more elusive. Antarctic zooplankton populations are dominated by krill — small, shrimplike animals that are the principal food of penguins, seals and whales. But krill are also in decline (Atkinson et al. 2004). Another zooplankton group, the gelatinous salps, is also present. Salps are voracious grazers and have few predators — they’re a sort of dead end in the marine foodchain. We used to believe that krill lived within the sea ice zone, but salps avoided it. The two groups were seldom found together. Recently we’ve found salps in nearly every net tow we’ve collected, including the samples with abundant krill and even in pack ice (Figure 2). Are we seeing a change in the ecosystem and its foodweb? Time will tell. Replacement of krill by salps would have important repercussions for the diet of larger predators.
Observations alone seldom reveal the full story. Observations are often sparse in space and time and complicated by technical difficulties in remote, harsh regions like the polar seas. To get more value from our data, we’re building mathematical models of Antarctic marine foodwebs, using the data we collect to calibrate and correct the model findings. We’re using a technique called inverse modeling to incorporate our observations into foodweb models that yield estimates of key ecosystem processes like photosynthesis, feeding, respiration and growth rates of krill, salps, penguins and bacteria. The emerging picture is surprising: it suggests that krill have been a relatively minor part of the foodweb since the beginning of the PAL time series (Ducklow et al. 2006).
Why do we care about foodchains so far away? The changes we’re seeing presage equally large changes closer to home. We will experience high CO2 in our atmosphere, and a warmer planet for centuries to come. Everything we can learn about these climate-related changes will help us adapt to an uncertain future.