A recent study performed by Elizabeth Harvey and Susanne Menden-Deuer at the University of Rhode Island provides evidence that microscopic aquatic plants called phytoplankton can both sense and move away from predators. In a lab-based experiment, the researchers put a specific type of phytoplankton (Heterosigma akashiwo, toxic algae that can cause red tide) in a tank. When they added members of a predator zooplankton species, the algae successfully moved away from their invaders. In another experiment, the phytoplankton moved away from water that previously contained predators, suggesting that there is a chemical cue that the algae use to sense their predators’ presence. Before this study, researchers knew that phytoplankton could move in response to light and to find nutrients, but this is the first report of algae sensing and escaping from predators.
These findings are especially important for toxic algae species like the one used in this study because they explain one reason for how large algae blooms begin. Some phytoplankton, like H. akashiwo, can survive in less salty water than many of their predators. This means H. akashiwo can swim to such waters to escape predators. Once they find themselves in safety, they are free to reproduce in massive quantities. Toxic algae blooms like red tide can decimate fish and other species. In 2006, a bloom of H. akashiwo wiped out $2 million dollars worth of farmed salmon in Puget Sound.
Another reason to study the movement of microscopic plants: phytoplankton make up the backbone of the ocean’s many food chains. A striking example of the importance of phytoplankton is this riveting story about algae which produced a potent neurotoxin that worked its way up an entire food chain and poisoned several humpback whales.
Phytoplankton also play a key role in removing carbon dioxide from the atmosphere and converting it to the oxygen we all love (and breathe). Thus learning more about what motivates these organisms to move across the ocean informs our knowledge of other ocean forces.
P.S. Another cool thing I learned while researching this post: NASA monitors red tides from space.