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Phytoplankton flee to avoid predators

Phytoplankton not only flee when in the presence of the predatory zooplankton, but they also flee when in water that had previously contained the predators, US scientists demonstrate
Credit:  
Heterosigma akashiwo is a swimming marine alga that episodically forms toxic surface aggregations known as harmful algal bloom
Scientists at the University of Rhode Island's Graduate School of Oceanography have made the first observation of a predator avoidance behavior by a species of phytoplankton.
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The phytoplankton can clearly sense the predator is there. They flee even from the chemical scent of the predator but are most agitated when sensing a feeding predator

— Susanne Menden-Deuer, associate professor of oceanography

Predation of phytoplankton effectively removes more than 50% of daily phytoplankton production in the ocean and influences global primary production and biochemical cycling rates.

However the effects of movement behaviors of either predator or prey on predation pressure, and particularly fleeing behaviors in phytoplankton are thus far unknown.

In a series of laboratory experiments, where researchers Menden-Deuer and Harvey tracked predator-prey interactions in three dimensions they noted that the phytoplankton Heterosigma akashiwo swam differently in the presence of predators, and groups of them shifted their distribution away from the predators.

They also found that the phytoplankton also flee when in water that had previously contained the predators. They found only a minimal effect when the phytoplankton were exposed to predators that do not feed on phytoplankton.

When the scientists provided the phytoplankton with a refuge to avoid the predator – an area of low salinity water that the predators cannot tolerate – the phytoplankton moved to the refuge. The important question these observations raise, according to Menden-Deuer, is how these interactions affect the survival of the prey species.

escape means survival
Measuring survival in the same experiments, the researchers found that fleeing helps the alga survive. Given a chance, the predators will eat all of the phytoplankton in one day if the algae have no safe place in which to escape, but they double every 48 hours if they have a refuge available to flee from predators. Fleeing makes the difference between life and death for this species, said Menden-Deuer.

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