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IN THE LABORATORY
Juhl has designed special Couette flow chambers that allow him to grow dinoflagellates in the gap between the two cylinders. He studies and records this growth by periodically removing a sample of water and counting the cells it contains.
He exposes dinoflagellates to very low levels of shear for an hour or more each day. Other Couette flow chambers remain stationary to serve as experimental controls. Juhl finds that the population growth rate, the rate at which the dinoflagellates are increasing in number, is much reduced in the sheared chambers compared with those that remain still.
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Juhl has studied the local red tide dinoflagellate species Lingulo-dinium polyedrum extensively, and is now working with Alexandrium fundyense, a toxic dinoflagellate that causes paralytic shellfish poisoning in other areas of the world, including the East Coast and the Pacific Northwest.
"This species causes huge economic losses to fisheries, and can make people sick,"Juhl explains. "When you expose the dinoflagellates to shear, their toxin levels go way up. So there might be fewer cells because of their decreased growth rate, but they might be more toxic." This may be important because cell counts of toxic species might not represent the potential toxicity of the seawater and shellfish during turbulent conditions.
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