The way by which living organisms in our planet are intricately connected is beautiful beyond comprehension. Like pieces in a puzzle they all fit together with the activities of each organism however trivial it may appear to be, affecting the existance of others. We will never fully understand this marvel, but a noteworthy example is the elegant finding by Lavery et al published in the Proceedings of the Royal Society (Biological Sciences)- Iron defecation by sperm whales stimulates carbon export in the Southern Oceanhttp://rspb.royalsocietypublishing.org/content/early/2010/06/14/rspb.2010.0863.full
The authors provide compelling evidence on the role that sperm whales (Physeter macrocephalus) in the Southern ocean play in promoting nutrient cycling and their function as carbon sinks. Lavery et al show that the whales consume prey at the depths of the ocean but expel the waste about 50 tonnes of iron iron-rich liquid buoyant faecal matter each year into the photic zone near ocean surface. The researchers estimate that if three quarters of this iron persisted there, 36 tonnes of iron to the photic zone per year are contributed by the activities of the Southern Ocean sperm whale alone. Iron is a nutrient essential for the growth of phytoplanton which live in the photic zone. Consequentially, iron enrichment causes phytoplankton blooms resulting in carbon export during photosythesis. Additionally, phytoplankton are consumed by zooplankton. The zooplankton are consumed by squids that form the food of the whales, thereby creating a positive feedback loop. Thus this toilette behaviour of the whale benefits it as well! The researchers estimate that sperm whales stimulated the export of 4 × 105 tonnes of carbon per year to the deep ocean whilst respiring 2 × 105 tonnes of carbon per year thereby mopping up carbon. This paper also highlights the issue as to how industrial whaling leading to large scale depletion of sperm whales might have impeded the ability of the Southern Ocean to act as a carbon sink.
Lavery, T., Roudnew, B., Gill, P., Seymour, J., Seuront, L., Johnson, G., Mitchell, J., & Smetacek, V. (2010). Iron defecation by sperm whales stimulates carbon export in the Southern Ocean Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2010.0863
At the end of the day there are very few ways yo get deep sea iron to the surface, and as the authors say, whales tend to congregate in the most productive areas so it is efficiently delivered. Whales - the worms of the ocean.
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