Southern Ocean iron fertilization by baleen whales and Antarctic krill

• Published in: Fish and Fisheries
• Main Authors: Nicol, S, Bowie, AR, Jarman, S, Lannuzel, D, Meiners, K, van der Merwe, P
• Format: Article in Journal/Newspaper
• Language: English
• Published: Blackwell Publishing Ltd 2010
• Subjects: Earth Sciences; Oceanography; Biological oceanography; Antarctic; Southern Ocean; The Antarctic; Antarc*; Antarctic Krill; baleen whale; baleen whales; Euphausia superba
• Online Access: http://onlinelibrary.wiley.com/doi/10.1111/j.1467-2979.2010.00356.x/abstract; https://doi.org/10.1111/j.1467-2979.2010.00356.x; http://ecite.utas.edu.au/67556

Iron is the limiting micronutrient in the Southern Ocean and experiments havedemonstrated that addition of soluble iron to surface waters results in phytoplanktonblooms, particularly by large diatoms. Antarctic krill (Euphausia superba) eat diatomsand recycle iron in surface waters when feeding. Baleen whales eat krill, and,historically, defecation by baleen whales could have been a major mechanism forrecycling iron, if whale faeces contain significant quantities of iron. We analysed theiron content in 27 samples of faeces from four species of baleen whale. Faecal ironcontent (145.9 +- 133.7 mg kg)1) is approximately ten million times that ofAntarctic seawater, suggesting that it could act as a fertilizer. Furthermore, weanalysed the iron content of seven krill species and of muscle tissue of two species ofbaleen whales; all samples had high iron levels. Using these figures, together withrecent estimates of the range and biomass of krill, we calculate that the Antarctic krillpopulation contains 24% of the total iron in the surface waters in its range. Thus,krill can act as a long-term reservoir of iron in Antarctic surface waters, by storingthe iron in their body tissue. Pre-exploitation populations of whales and krill musthave stored larger quantities of iron and would have also recycled more iron insurface waters, enhancing overall ocean productivity through a positive feedbackloop. Thus, allowing the great whales to recover might actually increase SouthernOcean productivity through enhancing iron levels in the surface layer.