In the spring of 2020, those lucky enough to be on the beaches of Southern California witnessed a phenomenon that left both scientists and the public in shock: a 'red tide' illuminated the water with stunning displays of reddish light. But behind this amazing and slightly disturbing spectacle lies a complex biological story. We used ChatGPT to explain what caused what is sometimes referred to in the media as a "blood stroke":
The breathtaking phenomenon was caused by the spread of Lingulodinium polyedra, a type of plankton known for its ability to emit a neon-blue glow. During the daytime, it makes the water appear red-brown, as if it has rust, and at night, every movement in the water causes it to emit blue light, so that it looks as if the waves and dolphins swimming in the water are surrounded by watery lightning.
However, the red tide also caused toxins and a drop in oxygen levels, which posed a threat to marine life and even led to mass fish deaths and severe ecological consequences.
A pioneering study led by researchers from the Scripps Institution of Oceanography at the University of California, San Diego and Jacobs School of Engineering has revealed the secret behind the extraordinary density of this plankton species during the red tide event. The discovery lies in the vertical swimming abilities of dinoflagellates, a group to which polyadra lingolodinium belongs. This unique feature has provided them with a competitive advantage over other phytoplankton species, and massive reproduction.
Oceanographer Drew Lucas, senior author of the study, said: "The idea that vertical swimming gives a competitive advantage to dinoflagellates actually goes back more than half a century, but only now do we have the technology to definitively prove it."
The vertical migration of dinoflagellates, a behavior that involves swimming upwards during the day for photosynthesis and downward at night to access nutrients, was carefully studied during the 2020 Red Tide event. The researchers deployed advanced instrumentation to collect an unprecedented amount of data, confirming the validity of a hypothesis first presented by Richard "Dick" Epley of Scripps Oceanography more than fifty years ago.
These microscopic organisms, equipped with whip-like external organs called flagella, exhibited extraordinary mobility. Their swimming speed, about 10 body lengths per second for nearly 24 hours, allowed them to dive to cold depths to extract nutrients. This unique feature, dubbed "fast burst swimming", played a major role in the intense spread of the red tide.
The research also harnessed new technologies, such as an autonomous profile analysis system and a robotic microscope. These instruments revealed the plankton's nocturnal journey into the depths, where they absorbed nutrients before resurrecting to bask in sunlight.
This important study confirms the hypothesis that Epley and colleagues assumed decades ago, and draws a direct link between dinoflagellate migration and harmful algal blooms. The study highlights the complex interplay of environmental conditions, biological behaviors, and ecological implications, and offers a clearer understanding of how these blooms occur and how they affect marine ecosystems.
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