Carbon fluxes and pelagic ecosystem dynamics around two western Antarctic Peninsula Adélie penguin colonies: an inverse model approach.

Using Palmer LTER data from annual summer sampling cruises, a food-web inverse model for the Western Antarctic Peninsula (WAP) pelagic food web was constrained, and model solutions were generated for two regions with Adélie penguin colonies presenting different population trends (a northern and a southern colony) for a 12 year period (1995-2006). Comparing carbon flow through bacteria, microzooplankton and krill showed that the diatom - krill - apex predator food chain is not the dominant pathway. The food web is more complex, including a food chain through microzooplankton and the microbial loop. Using both inverse model results and network indices, it appears that in North WAP the food web is dominated by the microzooplankton and the microbial loop, with a temporal trend toward increasing importance of the microbial loop. The dominant pathway for the South WAP food web varies from year to year with no detectable temporal trend toward dominance of one group of organisms or process over the rest of the food web. In addition, sensitivity analysis indicates that the north colony of Adélie penguins, whose population size has been declining in the past 35 years, appears to have enough krill during summer to sustain its basic metabolic needs and rear chicks, suggesting the importance of other processes in regulating the decline.