INVASION OF NORTH AMERICA BY THE DIATOM DISCOSTELLA ASTEROCOSTATA: MORPHOMETRIC AND RELATIVE ABUNDANCE ANALYSES FROM LAKES IN INDIANA AND ARKANSAS

Until recently, the diatom Discostella asterocostata had been observed only from localities in eastern China, southern Russia, South Korea, and Japan. However, several new studies have reported modern observations of the species in lakes from North America, despite no observations of the species from aquatic environments between the United States and Asia. Prior morphometric analyses of these disjunct species have confirmed that modern populations observed in lakes from in Arkansas and Indiana are morphologically indistinguishable from Asian populations. Here we expand these studies and analyze the relative abundance and morphometry of Discostella asterocostata from fossil diatom assemblages collected from recent (approximately the last 100 years) lake sediment records to determine the timing of the invasion of North America. Preliminary results suggest that a clear point of introduction occurs in sediment cores from multiple lakes in the late 20th century, followed by a gradual rise is relative abundance. Discostella asterocostata now appears to be one of the dominant planktonic species observed in the most recent sediments of several lake systems in this region.