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World - Massive plankton blooms with very different ecosystem impacts

"The big mystery about plankton is what controls its distribution and abundance, and what conditions lead to big plankton blooms," according to the author of a new study. Researchers explore this question and provide examples of conditions that lead to massive plankton blooms with vastly different potential impacts on the ecosystem.

Two new papers explore this question and provide examples of conditions that lead to massive plankton blooms with vastly different potential impacts on the ecosystem, according to McGillicuddy, co-author of both papers. Both papers also point to the importance of using advanced technology -- including Video Plankton Recorders, autonomous underwater vehicles, and the Ocean Observatories Initiative's Coastal Pioneer Array -- to find and monitor these blooms.

In one paper, Diatom Hotspots Driven by Western Boundary Current Instability, published in Geophysical Research Letters (GRL), scientists found unexpectedly productive subsurface hotspot blooms of diatom phytoplankton.

In the GRL paper, researchers investigated the dynamics controlling primary productivity in a region of the Mid-Atlantic Bight (MAB), one of the world's most productive marine ecosystems. In 2019, they observed unexpected diatom hotspots in the slope region of the bight's euphotic zone, the ocean layer that receives enough light for photosynthesis to occur. Phytoplankton are photosynthetic microorganisms that are the foundation of the aquatic food web.

It was surprising to the researchers that the hotspots occurred in high-salinity water intruding from the Gulf Stream. "While these intrusions of low?nutrient Gulf Stream water have been thought to potentially diminish biological productivity, we present evidence of an unexpectedly productive subsurface diatom bloom resulting from the direct intrusion of a Gulf Stream meander towards the continental shelf," the authors note. They hypothesize that the hotspots were not fueled by Gulf Stream surface water, which is typically low in nutrients and chlorophyll, but rather that the hotspots were fueled by nutrients upwelled into the sunlight zone from deeper Gulf Stream water.

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