Citation:

YOUNG, D. R., P. J. CLINTON, D. T. SPECHT, AND H. LEE, II. DOCUMENTING THE INTERTIDAL COMPONENT OF EELGRASS DISTRIBUTIONS IN PACIFIC NORTHWEST ESTUARIES USING COLOR INFRARED AERIAL PHOTOGRAPHY. Presented at 2007 Georgia Basin Puget Sound Research Conference, Vancouver, BC, CANADA, March 26 - 29, 2007.

Description:

The objective of this study was to develop and test a rapid, cost-effective method of mapping the intertidal (and surface-visible subtidal) distribution of eelgrass (Zostera marina L.) meadows and patches in the turbid coastal estuaries of the Pacific Northwest (PNW). Initial comparisons between true color and false-color near-infrared (color infrared, CIR) film indicated the clear advantage of CIR film in aerial photomapping surveys of this region. The photosurveys must be conducted in clear (or uniform high overcast) weather during daylight low tides, when substantial portions of eelgrass distributions in coastal estuaries are tidally exposed. The most reliable surveys are obtained in late spring before the summer blooms of benthic macroalgae that can interfere with accurate classification of intertidal eelgrass and bare substrate habitats. The technique reported here incorporates a hybrid approach toward digital classification of CIR photomap images, with a minimum mapping unit of 2.5 m x 2.5 m. Comparison of results with those from ground surveys in four Oregon estuaries yielded overall accuracies ranging from 83 to 100 percent. Best results were obtained when training surveys included GPS ground mapping of the upper margin of selected eelgrass meadows. Application of this technique should assist in the delineation and assessment of intertidal eelgrass distributions in the PNW, and factors that may stress this important estuarine habitat.

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