Algae discovery may shed light on red tide outbreaks

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Scientists know that phytoplankton – microscopic algae that serve as the base of the ocean’s food chain - often appear in thin, but immensely dense, sheets in the ocean that can extend for more than a mile.

These plant-rich regions serve as feeding hotspots for fish and other organisms – but also can harbor harmful blooms known as red tide that can wreak economic havoc on shellfish industries, including those in New England.  Now, research by MIT phD student William Durham and colleagues being published today in the journal Science is giving new insight into the mechanism of how these sheets form – and how different species of phytoplankton can get trapped, layer-cake like, in ocean currents. The findings could help researchers better understand how and where phytoplankton accumulates in the ocean and possibly address problems from fishery declines to red tide.

Ocean water layers flowing past each other can flip the strong phytoplankton swimmers and trap billions of them between water layers until a shift in wind or tide alters the currents and sets them free. Different species of phytoplankton, depending on their swimming ability and make-up, could get trapped in different ocean layers.

These layers form in the top 50 meters of the ocean and can be anywhere from a few centimeters to a couple of meters thick, span more than a mile horizontally and last hours, days or weeks, according to Durham, MIT Professor Roman Stocker and University of Arizona physics Professor John Kessler.

“Our research pinpoints a mechanism for the formation of these thin layers of phytoplankton, which are analogous to watering holes in a savanna — localized areas of concentrated resources that draw a wide range of organisms and thus play a disproportionate role in the ecological landscape,” said Stocker, the Doherty Assistant Professor of Ocean Utilization at MIT.