Abstract
An inverse food-web model for the western Antarctic Peninsula (WAP) pelagic food web was constrained with data from Palmer Long Term Ecological Research (PAL-LTER) project annual austral summer sampling cruises. Model solutions were generated for 2 regions with Adelie penguin Pygoscelis adeliae colonies presenting different population trends (a northern and a southern colony) for a 12 yr period (1995�2006). Counter to the standard paradigm, comparisons of carbon flow through bacteria, microzooplankton, and krill showed that the diatomkrilltop predator food chain is not the dominant pathway for organic carbon exchanges. The food web is more complex, including significant contributions by microzooplankton and the microbial loop. Using both inverse model results and network indices, it appears that in the northern WAP the food web is dominated by the microbial food web, with a temporal trend toward its increasing importance. The dominant pathway for the southern WAP food web varies from year to year, with no detectable temporal trend toward dominance of microzooplankton versus krill. In addition, sensitivity analyses indicated that the northern colony of Adelie penguins, whose population size has been declining over the past 35 yr, appears to have sufficient krill during summer to sustain its basic metabolic needs and rear chicks, suggesting the importance of other processes in regulating the Adelie population decline.
Highlights
Antarctic coastal waters exhibit high rates of primary production during a limited growing season of about 150 to 180 d (Smith et al 1996, 1998, Smith & Gordon 1997, Arrigo et al 1998, Vernet et al 2008)
The questions that we focused on through this study were (1) What are the differences between the northern and southern food webs? (2) What is the evolution and state of the system through the 12 yr period? (3) What is the importance of krill versus microbial processes? (4) Is the decline of the northern Adélie penguin colony explained by a decline in krill biomass or is the decline linked to other causes?
Our inverse model results indicated that the western Antarctic Peninsula (WAP) system is not dominated by the diatom−krill−apex predator food chain, primarily because microzooplankton ingested double the amount ingested by krill, and carbon flow through bacteria is equivalent to ~75% of the carbon ingested by krill
Summary
Antarctic coastal waters exhibit high rates of primary production (over 2 g C m−2 d−1 and 100 to 200 g C m−2 yr−1) during a limited growing season of about 150 to 180 d (Smith et al 1996, 1998, Smith & Gordon 1997, Arrigo et al 1998, Vernet et al 2008). Steinberg unpubl. data), and in some locations, a decline in populations of a top predator, the Adélie penguin Pygoscelis adeliae (Ducklow et al 2007, 2012)
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