Marine Phytoplankton Interesting Facts

BOTTOMS UP: How Whale poop helps feed the ocean

Large areas of the Southern Ocean are known as high-nutrient, low-chlorophyll (HNLC) waters. This is where Marine Phytoplankton abundance is very low despite high concentrations of major nutrients such as nitrate, phosphate and silicate.

Marine Phytoplankton is crucial in marine ecosystems as the main food source that supports all marine life. It also plays a key role in removing carbon dioxide from the atmosphere through photosynthesis.

Uneaten Phytoplankton eventually die and sink from the euphotic zone – the top 200-300m where light can penetrate – transferring the carbon to the deep sea.

One factor that limits the production of Marine Phytoplankton in high-nutrient, low-chlorophyll (HNLC) waters has been the availability of iron. Iron is an important nutrient that acts as an electron carrier and a catalyst during photosynthesis.

When iron is in short supply, Marine Phytoplankton can’t grow, leading to less carbon dioxide removed from the atmosphere.


During the short summer feeding season in the Southern Ocean, adult blue whales consume approximately two tonnes of krill per day. As they are accumulating blubber instead of building muscle to last them through the subsequent calving period, most of the iron consumed is excreted in their faeces.

The concentration of iron in whale faeces was found to be more than 10 million times higher than seawater concentrations. So whale poop acts as a fertiliser that increases Marine Phytoplankton growth leading to a more productive ecosystem and enhanced atmospheric carbon dioxide removal.

If whale populations had not been hunted to near-extinction, whales would have recycled more iron because of their abundant numbers.

In the Southern Ocean, iron defecation by the 12,000-strong population of sperm whales removes approximately 200,000 tonnes of carbon per year from the atmosphere!

Marine Phytoplankton Interesting Facts

Centre for Whale Research
Western Australia