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The bathymetric distribution of intertidal eelgrass Zostera marina L. in three coastal estuaries of Oregon
Citation:
YOUNG, D. R., P. J. CLINTON, D. T. SPECHT, T. MOCHON COLLURA, H. LEE, AND J. O. LAMBERSON. The bathymetric distribution of intertidal eelgrass Zostera marina L. in three coastal estuaries of Oregon. Presented at Pacific Estuarine Research Society annual meeting, Bellingham, WA, April 02 - 05, 2009.
Impact/Purpose:
Distributions of native eelgrass Zostera marina L. within the intertidal and shallow subtidal zones of three Oregon coastal estuaries (Tillamook, Yaquina, and Alsea) were determined by digital classification of aerial color infrared (CIR) orthophotographs.
Description:
Distributions of native eelgrass Zostera marina L. within the intertidal and shallow subtidal zones of three Oregon coastal estuaries (Tillamook, Yaquina, and Alsea) were determined by digital classification of aerial color infrared (CIR) orthophotographs. Stratified random surveys were conducted in the intertidal zones of these estuaries to aid in training the image analyst and to assess the accuracies of the resultant eelgrass and bare substrate classifications. Overall accuracies ranged from 84 to 100 percent. Substrate depth distribution data were used to produce bathymetric models for the estuaries and corresponding bathymetric distributions of the intertidal and shallow subtidal components of the eelgrass populations. The aerial photography mapping technique described here detected the shallow subtidal eelgrass to a depth of about - 1.8 m (- 6 ft) relative to the Mean Lower Low Water datum. Over 90 percent of the surface-visible eelgrass in the three modeled estuaries occurred within the depth interval - 0.9 m (- 3 ft) to + 0.9 m (+ 3 ft). Our findings, in conjunction with those of other studies, indicate that the average – 1.8 m (- 6 ft) detection limit depth for CIR aerial mapping in Oregon’s turbid coastal estuaries probably includes approximately 90 percent of the total eelgrass (intertidal and subtidal) distribution typically found in such coastal ecosytems. These results support the use of CIR aerial orthophotography in determining, and monitoring changes in, the distribution of native eelgrass with coastal development, sea level rise, and other stresses on coastal estuaries of Oregon.