The Operational Land Imager on Landsat 8 captured this view of a phytoplankton bloom near Alaska’s Pribilof Islands in the Bering Sea on Sept. 22, 2014. The water’s milky green and light blue shading indicates the presence of vast populations of microscopic phytoplankton.
Blooms in the Bering Sea increase significantly in springtime, after winter ice cover retreats and nutrients and freshened water are abundant near the ocean surface. Phytoplankton populations plummet in summertime as the water warms; surface nutrients are depleted by blooms; and the plant-like organisms are depleted by grazing fish, zooplankton and other marine life. By autumn, storms can stir nutrients back to the surface, and cooler waters make better bloom conditions.
Mike Behrenfeld, a phytoplankton ecologist at Oregon State University, has been researching the “dance of the plankton,” revealing that it’s more complicated than previously suspected. Together with colleagues at four institutions, Behrenfeld has developed a “disturbance-recovery hypothesis” in which blooms tend to be started by any process that disturbs the natural balance between phytoplankton and their predators.
“Phytoplankton are rubberbanded to their predators,” says Behrenfeld. “As long as phytoplankton are accelerating in their division rate, they’ll stay ahead. As soon as they slow down, the predators that have been increasing along with the phytoplankton will quickly catch up, stop the bloom by consuming the phytoplankton, and then begin decreasing the numbers of phytoplankton.”
Earth observation data from NASA’s Moderate Resolution Imaging Spectrometer have provided valuable input to this research. The mix and bloom cycle research is important, suggesting that with the oceans warming, a decrease in ocean mixing will occur that will significantly decrease phytoplankton stocks.