Warming of the sea surface by as little as several tenths of a degree can pose a serious threat to King penguins. This was shown in a new report by the team of Yvon Le Maho, CNRS senior researcher at the Institut pluridisciplinaire Hubert Curien (IPHC, CNRS / University of Strasbourg 1) and a member of the French Academy of Sciences. The researchers tracked more than 450 individual King penguins over nine years in their natural environment, within the Crozet Archipelago.
The research was carried out together with researchers from the Centre d'écologie fonctionnelle et évolutive, from the biological station at Tour du Valat, from the Muséum national d'histoire naturelle de Paris and the University of Oslo, is published in PNAS. The first author, Céline Le Bohec, is now with the group in Oslo for a post-doc.
How to track penguins in their natural environment
For years, a numbered band attached on a flipper was used to track individually penguins, but these bands increased the drag of pengouins when moving into water. The "Écologie fonctionnelle" team, led by Yvon Le Maho at IPHC, observed that adult king penguins wearing a flipper band had their breeding success reduced by half. They also showed that the survival of unbanded chicks was increased by half. To avoid this bias on the scientific data, the IPHC team put together an innovative system allowing long-term tracking of the king penguins with no impact on how the penguins interact with their natural environment.
The new system is based on individual electronic identification. The study was initiated 9 years ago, covering a population of 450 king penguins who had had an 0.8 g electronic tag implanted under their skin. The tagged birds could then be identified thanks to antennas buried along the “Penguin highways”. The research was carried out on Ile de la Possession in the Crozet Archipelago, where 2/3 of the world population of king penguins is breeding (some 2 million penguins). The data are thus representative for the entire population.
Why king penguins?
Being able to predict the impact of climate change on biodiversity is vital, but the effects on marine productivity in the Southern Ocean are still poorly understood. Furthermore, it is difficult to determine the impact of climate on marine food chains. One of the advantages of pelagic birds is that they are predators, and thus at the top of the food chain, and as a result, their population dynamics reflect the change in marine resources. As penguins obviously do not fly, great numbers of them can be identified and localized on their usual routes. Additionally, it is only king penguins that commute regularly all throughout the year between the colony and the ocean, where they find food for themselves and their chicks.
During the summer, the penguins forage at a distance between 300 and 600 km from their colony, the distance being directly correlated with the warming of the Ocean: the warmer the surface water, the fewer fish prey close to Crozet and the further the penguins must go. In winter, when marine resources are more difficult to come by, the penguins must go some 2000 km from the colony, near the ice seas off of Antarctica.
Direct effect on breeding success and the survival of penguins
The first observation is that warming of the sea surface near Crozet in the summer leads to an immediate drop in the breeding success of the king penguins. This worrying phenomenon can be explained by the fact that a higher temperature hinders the development of marine organisms, which can only prosper at a narrow range of temperatures. When king penguins bring less food back to their chicks, they have reduced chances of survival.
The second observation, this time during winter, is that an increase of only 0,26°C in the ocean surface temperature, at the edge of the ice sea, leads two years later to a 9% drop in the probability of penguins’ survival. This too is a result of a decrease in marine resources, most probably of krill, which is at the bottom of Antarctic food chains, and which the king penguins need for survival.
Considering that the IPCC is predicting an average temperature increase of approximately 0,2°C per decade for the next two decades, the warming of the Southern Ocean will be a serious threat to the king penguin populations. Will the penguins survive? Will they adapt to future climate change?
Journal reference: King penguin population threatened by Southern Ocean Warming. Céline Le Bohec, Joël M. Durant, Michel Gauthier-Clerc, Nils Chr. Stenseth, Young-Hyang Park, Roger Pradel, David Grémillet, Jean-Paul Gendner and Yvon Le Maho. PNAS. 11 February 2008.
This research was supported by the Institut polaire français Paul-Émile Victor (IPEV).
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