Critical indirect effects of climate change on sub‐ Antarctic ecosystem functioning

• Published in: Ecology and Evolution
• Main Authors: Louise Allan, E., William Froneman, P., Durgadoo, Jonathan V., McQuaid, Christopher D., Ansorge, Isabelle J., Richoux, Nicole B.
• Other Authors: South African Department of Environmental Affairs and Tourism, National Research Foundation, Rhodes University, Deutscher Akademischer Austausch Dienst, Andrew Mellon Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2013
• Subjects: Antarctic; Antarc*
• Online Access: http://dx.doi.org/10.1002/ece3.678; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fece3.678; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ece3.678

Abstract Sub‐ A ntarctic islands represent critical breeding habitats for land‐based top predators that dominate S outhern O cean food webs. Reproduction and molting incur high energetic demands that are sustained at the sub‐ A ntarctic P rince E dward I slands ( PEI s) by both inshore (phytoplankton blooms; “island mass effect”; autochthonous) and offshore (allochthonous) productivity. As the relative contributions of these sustenance pathways are, in turn, affected by oceanographic conditions around the PEI s, we address the consequences of climatically driven changes in the physical environment on this island ecosystem. We show that there has been a measurable long‐term shift in the carbon isotope signatures of the benthos inhabiting the shallow shelf region of the PEI s, most likely reflecting a long‐term decline in enhanced phytoplankton productivity at the islands in response to a climate‐driven shift in the position of the sub‐ A ntarctic F ront. Our results indicate that regional climate change has affected the balance between allochthonous and autochthonous productivity at the PEI s. Over the last three decades, inshore‐feeding top predators at the islands have shown a marked decrease in their population sizes. Conversely, population sizes of offshore‐feeding predators that forage over great distances from the islands have remained stable or increased, with one exception. Population decline of predators that rely heavily on organisms inhabiting the inshore region strongly suggest changes in prey availability, which are likely driven by factors such as fisheries impacts on some prey populations and shifts in competitive interactions among predators. In addition to these local factors, our analysis indicates that changes in prey availability may also result indirectly through regional climate change effects on the islands' marine ecosystem. Most importantly, our results indicate that a fundamental shift in the balance between allochthonous and autochthonous trophic pathways within this island ecosystem ...