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The Rebound Effect: Student Studies DEET’s Effect on Dinoflagellates

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Ryan studied dinoflagellates in near-complete darkness experimentation areas. Photo courtesy of Ryan.

Puerto Rico is one of the few places on Earth with bioluminescent bays. A favorite destination for tourists, these inlets glow at night when swimmers agitate the waters’ light-emitting dinoflagellates, or tiny photosynthetic microbes.

Seventeen-year-old Ryan wanted to understand whether the popular insect repellant DEET, worn by many tourists to ward off mosquitoes, had any effect on the dinoflagellates in these bays. His investigation, outlined in the essay The Effects of DEET on the Bioluminescent Dinoflagellate, Pyrocystis fusiformis, earned Ryan one of this year’s Young Naturalist Awards.

Ryan hypothesized that the presence of DEET in the water would adversely affect the dinoflagellates’ ability to luminesce. To test his prediction, Ryan used black garbage bags and duct tape to convert wooden shelves into near-complete darkness experimentation areas. He added several solutions with varying concentrations of DEET to flasks filled with dinoflagellates, also monitoring a control group that contained distilled water. After setting a timed lamp to mimic 12-hour cycles of daylight and darkness, Ryan agitated each culture with a swirl and measured their illuminance with a light sensor.

Upon recording the dinoflagellates’ maximum illuminance each day, Ryan realized his results did not support his hypothesis. While dinoflagellates exposed to the lower (.01 to .1 percent) concentrations of DEET emitted significantly less light than the control group on the first day of the trial, they rebounded on the second day and performed as well as the control throughout the rest of the experiment. The dinoflagellates that experienced the highest concentration of the repellant (1 percent) died, leading Ryan to conclude that these organisms may rebound from the stresses of DEET up to a certain threshold.

Ryan acknowledges the limits of his investigation and hopes he can conduct another one in the future that would take into account the amount of DEET that leaves a swimmer’s skin and enters the water. This information, he believes, “would aid scientists and conservationists in evaluating the policies regarding swimming in some bioluminescent bays.”

To learn more about bioluminescent bays and to see live dinoflagellates, visit the Museum’s exhibition Creatures of Light: Nature’s Bioluminescence, which will open on March 31, 2012.

The Young Naturalist Awards is a nationwide, science-based research contest for students in grades 7 through 12 presented by the Museum. To learn more and to submit your own project, visit The deadline for the 2012 contest is March 9, 2012.

The Young Naturalist Awards are proudly supported by Alcoa Foundation.