Phytoplankton waiting game perhaps key to their success in ocean deserts

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File:Survival Technique.JPGIn survival situations people often talk about the rule of three. It is said that humans can only survive for 3 minutes without air, 3 hours without heat, 3 days without water and 3 weeks without food. Not wanting to be left out, it seems that some phytoplankton also obey a rule of 3 according to a new study: they can survive for 3 weeks without key nutrients such as nitrogen and phosphorus.

The phytoplankton in question are a species of dinoflagellate called Neoceratium, and this ability to go for long periods of time without nutrients probably gives them a big advantage in parts of the ocean where nutrients are in incredibly low concentrations, such as in the subtropical gyres (often called, ocean deserts). Here, there are very few inputs of nutrients into surface waters as the subtropical gyres are located far from the land, and year-round high temperatures prevent surface waters mixing with nutrient-loaded deeper waters. Most phytoplankton in this environment are very small, which helps them survive, as they can take-up nutrients at low concentrations. Neoceratium are large though, so their presence in the gyres is a little bit puzzling. But this new study helps shed some light on this mystery.

An image of Neoceratium

In the study Neoceratium were exposed to ever increasing lengths of time without nutrients. Then nutrients were added to see if cells could still grow. Beyond 10 days without nutrients, cells started to show signs of stress, but at least some cells kept recovering all the way up to 26 days.  The authors suggest that this is a useful adaptation to life in subtropical gyres, allowing cells to access nutrients sources periodically. These nutrient sources may include at least one of the following:

1)      Periodic events where eddies (ocean storms) mix nutrients into the surface waters

2)      Transport of cells from sunlit surface waters to nutrient-rich deeper waters

3)      Occasional feeding on other organisms to obtain nutrients

Original paper:

Growth and survival of Neoceratium hexacanthum and Neoceratium candelabrum under simulated nutrient-depleted conditions

 

David Aldridge has a PhD in Marine Science from The National Oceanography Centre, Southampton. He is now planning his escape from academia. He is the founder and editor of Words in mOcean.

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