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. 2014 Dec 3;9(12):e114067.
doi: 10.1371/journal.pone.0114067. eCollection 2014.

The Biogeochemical Role of Baleen Whales and Krill in Southern Ocean Nutrient Cycling

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The Biogeochemical Role of Baleen Whales and Krill in Southern Ocean Nutrient Cycling

Lavenia Ratnarajah et al. PLoS One. .
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The availability of micronutrients is a key factor that affects primary productivity in High Nutrient Low Chlorophyll (HNLC) regions of the Southern Ocean. Nutrient supply is governed by a range of physical, chemical and biological processes, and there are significant feedbacks within the ecosystem. It has been suggested that baleen whales form a crucial part of biogeochemical cycling processes through the consumption of nutrient-rich krill and subsequent defecation, but data on their contribution are scarce. We analysed the concentration of iron, cadmium, manganese, cobalt, copper, zinc, phosphorus and carbon in baleen whale faeces and muscle, and krill tissue using inductively coupled plasma mass spectrometry. Metal concentrations in krill tissue were between 20 thousand and 4.8 million times higher than typical Southern Ocean HNLC seawater concentrations, while whale faecal matter was between 276 thousand and 10 million times higher. These findings suggest that krill act as a mechanism for concentrating and retaining elements in the surface layer, which are subsequently released back into the ocean, once eaten by whales, through defecation. Trace metal to carbon ratios were also higher in whale faeces compared to whale muscle indicating that whales are concentrating carbon and actively defecating trace elements. Consequently, recovery of the great whales may facilitate the recycling of nutrients via defecation, which may affect productivity in HNLC areas.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.


Figure 1
Figure 1. Metal to carbon ratios in krill and whales (μmol mol−1).
Data points above the third quartile for whale faeces are 3 or more times higher than the interquartile range.
Figure 2
Figure 2. Carbon to phosphorus ratio in krill and whales (mol mol−1).
Data point above the third quartile for whale faeces is 3 or more times higher than the interquartile range.

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Grant support

This work was supported by the Australian Government's Cooperative Research Centres Programme through the Antarctic Climate and Ecosystem Cooperative Research Centre, by the Australian Antarctic Division and by the Australian Marine Mammal Centre. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.