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Expansion of the invasive dwarf eelgrass, Zostera japonica, in Yaquina Bay, Oregon
YOUNG, D. R., P. J. CLINTON, D. T. SPECHT, AND T. MOCHON COLLURA. Expansion of the invasive dwarf eelgrass, Zostera japonica, in Yaquina Bay, Oregon. Presented at Coastal and Estuarine Research Federation Biennial Conference, Daytona beach, FL, November 06 - 10, 2011.
The areal coverage of the non-indigenous dwarf eelgrass, Zostera japonica, is increasing in several estuaries on the US West Coast.
The areal coverage of the non-indigenous dwarf eelgrass, Zostera japonica, is increasing in several estuaries on the US West Coast. As a result, regulatory agencies in the states of California and Washington are considering methods of controlling its expansion. Factors relevant to this effort are specific zones of an estuary where Z. japonica gains a foothold and the rate at which it expands its range. Here we describe the results of a decade-long study of the spatial distribution of dwarf eelgrass in Yaquina Bay, USA. The method used was classification of digital orthophotographs obtained during aerial photography surveys with false color near-infrared film, conducted during daytime low tides in the spring and summer growing seasons. A comparison of classification and ground survey results for dwarf eelgrass cover vs. bare substrate yielded an overall accuracy of 83%. In Yaquina Bay this invasive eelgrass first appeared in the upper intertidal zone and gradually moved downslope over the years. Highest cover densities initially were found near small streams of freshwater runoff, suggesting that this source may be important to its establishment. Estimates of the rate of spread of dwarf eelgrass in lower Yaquina Bay are presented.