Ecosystem iron retention and recycling in the pelagic phase via top predators

Iron availability is the main limiting factor on the primary production in the Antarctic marine ecosystem. The “whale pump” hypothesis argues that marine mega-fauna, such as whales, indirectly boost primary production by increasing the amount of accessible iron in the pelagic phase via “recycling” (e.g., defecation and mortalities). This “whale pump” posits a positive feed-back loop, not only between whales and primary producers, but with ripple effect to higher trophic levels in the ecosystem, including commercial fish species. If this hypothesis is correct, expanding whale populations to their historic, pre-whaling levels could have far-reaching, ecosystem-wide effects; such as increasing the overall carrying capacity of the ecosystem, as well as buffering the negative effects of global warming by increasing carbon sequestration in the ocean. The plausibility of this hypothesis, and its potential effects on a changing environment, can be assessed by back-casting whale, fish, krill and zooplankton population dynamics after the Last Glacial Maximum (LGM, 15 – 20,000 years ago (kya)). Genome-level data and habitat availability changes from ecological niche modelling can be employed to assess the relative changes in habitat and species abundances as the oceans warmed. A positive feed-back loop (i.e., a whale pump) would have resulted in higher rates of change abundances than rates predicted from increased habitat availability only. This approach, by combining genomics and ecological modelling, could not only confirm the “whale pump” hypothesis but also provide fundamental, key insights into the ecosystem dynamics in the Antarctic and its likely future in response to the current global warming.