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Invasion of the Jellyfish

Photo: Nemopsis bachei by Genelle Harrison

Few people would be willing to wake up in the wee hours of the morning to drive hours away to collect samples of hydromedusae—a nearly transparent, minuscule type of jellyfish—in five-foot swells. But this early morning ritual has become routine for Genelle Harrison, a graduate student finishing her master's degree in biology at American University.

Harrison works with her two advisors, environmental science professor Kiho Kim and Allen Collins from the National Systematic Laboratory of the National Oceanic and Atmospheric Administration (NOAA), comparing the DNA of hydromedusae to infer invasive patterns between the populations of different regions. Her work is funded by the Smithsonian Institution and a Hemlinge Award.

Dividing her time between the Smithsonian's Laboratory of Analytical Biology and Kim's lab, Harrison compares the DNA of her samples from one geographic region to samples from other geographic regions, with samples being used from North and South American coasts. Harrison hypothesizes that populations of jellyfish that move between estuaries will have higher genetic variation because they are interbreeding with one another, while isolated populations will be more genetically similar because there is less biodiversity.

Three mitochondrial genes and two nuclear genes are targeted in Harrison's study. Mitochondrial genes tend to evolve faster than nuclear genes, which is vital to the progress of her research. The first record of hydromedusae in the Americas dates back to the late 1800s. Since 100 years is a very short period of time in evolutionary history, Harrison must use genes that evolved quickly to find genetic changes between hydromedusae in different geographic regions. This will ultimately show whether or not the populations are isolated or freely moving between regions.

While it is generally assumed that the hydromedusae samples are invasive, Harrison hopes her research will provide information on monitoring the movements of the cnidarians. It is important to know where the organisms are being introduced, where they are spreading to, and their degree of genetic diversity. When these results are documented, management protocols can be created to protect local zooplankton populations upon which these organisms feed.

Adapted from "Invasion of the Cnidaria: Understanding the Patterns of Distribution of Hydrozoan Jellyfish," in the spring 2010 issue of Catalyst.