Blue waves made quite a splash along the coast off southern California earlier this year, but it’s not an unusual phenomenon and it’s not unique to the area (though it was the biggest there in a decade).
Every few years, a bloom of microscopic organisms called dinoflagellates transforms coasts around the world in a similar way – and now an international team led by the University of Cambridge, UK, says it has identified the underlying physics that makes it happen.
Raymond E Goldstein and colleagues developed tools based on micromanipulation and high-speed imaging to visualise light production on the single-cell level.
They showed how a single-celled organism of the species Pyrocystis lunula produces a flash of light when its cell wall is deformed by mechanical forces, and that the brightness of the flash depends both on the depth of the deformation and the rate at which it is imposed.
Known as a “viscoelastic” response, this behaviour is found in many complex materials such as fluids with suspended polymers. In the case of dinoflagellates, the researchers say, it is most likely related to ion channels – specialised proteins distributed on the cell membrane.
When the membrane is stressed, these channels open up, allowing calcium to move between compartments in the cell, triggering a biochemical cascade that produces light.
“Our findings reveal the physical mechanism by which the fluid flow triggers light production and show how elegant decision-making can be on a single-cell level,” says Maziyar Jalaal, first author of a paper in the journal Physical Review Letters.
The study shows that when the deformation of the cell wall is small, the light intensity is small no matter how rapidly the indentation is made, and it is also small when the indentation is large but applied slowly. Only when both the amplitude and rate are large is the light intensity maximised.
The group’s mathematical model was able to explain these observations quantitatively, and they suggest that this behaviour can act as a filter to avoid spurious light flashes from being triggered.
In the meantime, the researchers plan to analyse more quantitatively the distribution of forces over the entire cells in the fluid flow, a step towards understanding the light prediction in a marine context.
The work brought together scientists from Cambridge, the Max-Planck Institute for Dynamics and Self-Organisation in Germany, and France’s Ècole Polytechnique and Institut de Physique de Nice.
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