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ESTIMATING DENSITIES OF ESTUARINE EELGRASS AND BENTHIC MACROALGAE VIA AERIAL PHOTOGRAPHY
Citation:
Young, D R., D T. Specht, AND P J. Clinton. ESTIMATING DENSITIES OF ESTUARINE EELGRASS AND BENTHIC MACROALGAE VIA AERIAL PHOTOGRAPHY. Presented at Estuarine Research Federation meeting, Seattle, WA, September 14-18, 2003.
Description:
The goal of this research was to distinguish meadows of native eelgrass (Zostera marina L.) from adjacent beds of benthic green macroalgae in the exposed intertidal zone of Pacific Northwest estuaries, using false-color near-infrared aerial photography. Aerial photographs of Yaquina Bay estuary, Oregon, were taken during a minus tide at a photo scale of 1:7200 and digitally orthorectified with a ground pixel resolution of 20 cm. to provided photomaps of the aquatic vegetation. Using 1 m2 quadrats, more than 200 ground stations were surveyed within one week of the photography to obtain percent cover measurements of Z. marina, green macroalgae (principally Enteromorpha spp. and Ulva spp.), or bare substrate. Stations were DGPS positioned with an rmse accuracy of +/- 60 cm. A digital image classification method was developed synthesizing the techniques of band-ratio vegetation indices, unsupervised classification and on-screen photo-interpretation to classify vegetation at the pixel scale. Classified pixel percentages for 5 m2 samples at each of the ground stations were compared to the percent cover values measured by the ground survey. On average, the cover densities calculated from the digital classification were about 25 percent lower for both eelgrass and green macroalgae than those of the ground survey.