When you think about grazing, you picture a big mammal with hooves eating a helpless plant – placidly chewing and digesting, right? Well, there’s another kind of grazing that is much more dynamic. Researchers at the University of Rhode Island have, for the first time known to science, discovered a plant that “runs away” to avoid being munched. The tiny Heterosigma akashiwo you see above on the right, not only makes tracks when predators like the Favella favella are after it (the big, mouthy guy on the left), but it will even avoid areas where there used to be predators, but no longer are. They are, in effect, fleeing the scent of danger.
Before you stand up and cheer for the little guy, you should know that this particular plant is one of the “red tide” phytoplankton that can cause major fish kills when it blooms. Dr. Susanne Menden-Deuer, an oceanography professor who studies the plankton at the University of Rhode Island, speculates that its ability to flee may be one of the mechanisms that allow Heterosigma to grow prolifically enough to kill fish. The plant, a type of algae, will take refuge in areas with lowered salinity – places where its predators cannot survive. As the algae move into these areas of refuge, they are free to reproduce with little to check their population explosion.
These harmful algal blooms can cause major devastation and millions of dollars in economic damage to fisheries – killing not only finfish like salmon and herring, but also harming oysters, copepods, and sea urchins.
Usually, though, Heterosigma are not harmful at all, blooming only occasionally in spring and fall. In fact, they provide many benefits to us – they are an important food source at the bottom of our productive ocean food chain. Not only that, but phytoplankton are responsible for giving us the oxygen in half the air we breathe.
Menden-Deuer plans to conduct further research to find out what the connections are between the fleeing behavior and harmful algal blooms, and if other plants might be up to this evasive behavior.
Photo credit: Elizabeth Harvey (URI-GSO). Digital enhancement by Cynthia
Beth Rubin (RISD).