The western peninsula of Antarctica is home to one of the most diverse and abundant aquatic ecosystems. This area is also one of the most susceptible to climate change with 5-6 °C increases in mean winter air temperature and subsequent decreases in sea-ice. Trivelpiece et al. (2011) looked at two penguin species, Adélie and chinstrap penguins, and their unusually linked trends in population trajectory. The authors studied these two penguin species on the Western Antarctic Peninsula (WAP) in order to link decreasing biomasses in Antarctica Krill to the declining penguin populations. An interesting aspect of the decline of these two species is that Adélie penguins favor pack-ice in the winter and the chinstrap penguins favor ice-free water during winter, but both species are experiencing population declines. The scientists found that the decline of both can be explained by decreasing krill biomass owing to climate change and increased krill predation from humans and whales. Trivelpiece et al. suggest that the Krill harvesting be monitored more closely and that the chinstrap penguin be monitored by the International Union for the Conservation of Nature as a vulnerable species. –Connor O’Boyle
Trivelpiece. W., Hinke, J., Miller, A., Reiss, C., Trivelpiece, S., Watters, G.,2011. Variability in krill biomass links harvesting and climate change to penguin population changes in Antarctica. Proceeding of the National Academy of Science of the United States of America 108, 7625—7628.
The sea-ice in Antarctica plays a crucial role in the marine ecosystem, regulating diet and creating habitat for many organisms. As sea-ice has been declining the populations of Adélie and chinstrap penguins have declined more than 50%. The authors analyzed the previous thirty years of studies and found that before 1987 the size of these populations, due to their different preference in winter feeding, were negatively correlated. However, since 1987, both species have declined together. These contrasting patterns can be explained by recruitment trends. In the earlier period with the negative correlation, the winters with increased sea-ice had increased numbers of juvenile Adélie penguins returning to breed. Whereas winters with decreased ice had increased numbers of juvenile chinstrap penguins returning. In the most current period, both species have experienced large declines in juvenile survival and there is no longer a large flux between populations. The authors note similar population declines throughout the Scotia Sea so their WAP data are not anomalies.
Antarctic krill are the dominant prey of an almost every top predator in the Antarctic marine environment. It has been estimated that 150 million tons of krill were available to support top predators such as penguins. The penguin populations of many species increased dramatically during the years in which human hunting dramatically decreased whale populations around the world. The authors found, by analyzing the Adélie penguin diet using fossil eggshell material in extinct colonies, that an abrupt shift happened in the last 200 years from a mainly fish diet to a mainly krill diet. This could be a good thing for the Adélie penguins but the scientists say it is not certain whether these penguins could switch back to their previous diet. Currently both the Adélie and chinstrap penguins are heavily dependent on krill; even though the krill biomass has significantly been reduced both species rely almost solely on it. The reproductive success of krill has been linked to sea-ice extent, and the decrease in ice accumulation related to global warming correlated with a large decline in krill in Antarctica. In addition krill fishery has increased from 50,804 tons in 2002—2003 to 202,346 tons in 2009—2010. Because to new products are being made from krill, including Omega-3 pills, the krill fishery is poised to expand, further stressing penguin populations.
The authors conclude with a warning that with increased fishing and warmer Antarctic winters, krill populations will continue to decline and with them the Adélie and chinstrap penguin populations. Trivelpiece et al. suggest thatchinstrap penguins could be the more vulnerable of the two due to their restricted range and historic dependency on krill.