Oceanic turbulence affects marine food web

Numerical simulations have shown for the first time that the movement of seawater can directly affect the ability of marine bacteria to absorb organic material, such as that produced by phytoplankton. Bacteria are consumed by large organisms and therefore the organic material contributes to the functioning of the marine food web.  The study looks at the relationship between the natural movement of water within the ocean and the ability of marine bacteria to act as recyclers.

Computer models of different scenarios suggested that a delicate balance exists between the degree of oceanic turbulence and the recycling activity of bacteria – with high and low levels of turbulence associated with lower recycling rates.

The study showed that organic matter enters the water in bursts, after which natural ocean turbulence causes a stirring action, dispersing it.

“When you pour cream into coffee and stir it carefully, you get swirls of cream. Something similar happens – on a tiny scale- when bursts of organic matter enter gently moving water. The swirls of organic matter are easily accessed by swimming bacteria which surround and absorb it. If you mix cream into your coffee vigorously, it quickly becomes dispersed. When this happens in an area of the ocean, the swimming bacteria have less to gain in seeking out the thinly-dispersed organic matter,” explained Dr John Taylor from the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge.

The research, published in Science, also investigated the way in which the physical environment of the ocean might select bacteria with specific adaptations. Some bacteria have the ability to swim which gives them advantages over less motile species when foraging for food.  Additionally, some bacteria can detect and respond to chemicals dissolved in surrounding water, a trait known as chemotaxis.

“Our research suggests that the optimum environment for chemotaxis is one of the intermediate turbulence intensity – when the bursts or organic matter as stirred into thin filaments which can be exploited by large numbers of bacteria. The best environment for motile bacteria is one in which the organic matter is lightly stressed into the water rather than vigorously mixed,” said Dr Taylor.

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