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Distribution of intertidal eelgrass (Zostera marina L.) with bathymetry in three Pacific Northwest estuaries
Citation:
YOUNG, D. R., P. J. CLINTON, D. T. SPECHT, T. MOCHON COLLURA, AND H. LEE, II. Distribution of intertidal eelgrass (Zostera marina L.) with bathymetry in three Pacific Northwest estuaries. Presented at Biennial Conference of the Coastal and Estuarine Research Foundation, Portland, OR, November 01 - 05, 2009.
Impact/Purpose:
Distributions of native intertidal eelgrass (Zostera marina L.) and non-vegetated substrates in three coastal estuaries of the Pacific Northwest (PNW) were determined using color infrared (CIR) aerial orthophotography during daylight low tides.
Description:
Distributions of native intertidal eelgrass (Zostera marina L.) and non-vegetated substrates in three coastal estuaries of the Pacific Northwest (PNW) were determined using color infrared (CIR) aerial orthophotography during daylight low tides. Comparison of the digital classifications with results of stratified random surveys in Tillamook, Yaquina and Alsea estuaries yielded overall accuracies of 84%-100%. Bathymetric survey data (relative to MLLW datum) were used to produce bathymetric models for the estuaries and corresponding bathymetric distributions of the intertidal and shallow subtidal components of the eelgrass populations. These models indicated that eelgrass growing to a depth of about – 1.8 m (- 6 ft) is detectable using this technique. More than 90% of the classified eelgrass habitat occurred within the depth interval – 0.9 m to + 0.9 m (- 3 ft to + 3 ft) in all three estuaries. Extrapolation of the bathymetric distributions to the maximum depths of eelgrass occurrence measured from ground surveys suggested that this technique captures more than 90% of the total eelgrass distributions. Average bathymetric distributions between – 1.8 m and + 1.8 m within 100 m along-channel segments were determined and compared. Measurable eelgrass occurred at upstream locations corresponding to average winter salinities as low as ~ 5 psu. These results show the utility of CIR aerial orthophotography and high-resolution bathymetry in characterizing estuarine benthic habitats, and monitoring changes in the distribution of native eelgrass with coastal zone development, sea level rise, and other stresses on PNW turbid coastal estuaries.