Dataset: Eelgrass shoot density measurements taken during ecological field surveys along the eastern Pacific coast in June through August of 2019, 2020, and 2021.

Field surveys of eelgrass meadow sites were conducted at mid-summer low tides at field sites along the west coast of North America in the U.S. and Canada.  Samples and data were collected within the intertidal area of 32 eelgrass meadows distributed in six regions (Alaska, British Columbia, Washington, Oregon, California -Bodega Bay, and California -San Diego). Surveys were conducted between late June and early August in 2019, 2020, and 2021 by teams from six institutions.

For each site, three 20 meter transects were laid parallel to the shore at the shoreward (upper edge) of continuous eelgrass, and three lower (intertidal) 20 meter transects were laid at least 4 meters closer to the water.  Shoot density and canopy cover were measured at meters 4, 8, 12, and 16.  At each meter, a PVC quadrat was placed on the upper (landward) side of the transect tape, aligning the lower left corner of the quadrat with the meter mark.  The percent cover within the quadrat area was recorded for seagrass, bare sediment, and other (macroalgae unless noted otherwise).  Shoot densities, categorized by the number of vegetative and flowering shoots, were then counted.  Only shoots rooted in the quadrat were included in the density counts.  Quadrats for shoot density range in size from 0.0625 to 0.36 square meters.  Quadrats for cover ranged in size from 0.09 to 1 square meter.  Quadrat size was determined by expert judgment of the practitioners at each field site.  

Transect locations were recorded using a hand-held GPS (exact model varied between field locations). Salinity was measured at the time of sampling using a refractometer. Temperature loggers (HOBO MX 2201 and UA-001-64, Onset, Bourne, MA) were deployed at each eelgrass meadow site to provide a continuous record of in situ temperature.  For HOBO data, see https://www.bco-dmo.org/dataset/877355 and Related Datasets section below.

~ For methodology details, see Aoki et al. (2022)
~ Additional details for the field surveys are available in the Eelgrass Disease Project Handbook.
~ For 16S rRNA amplicon sequencing of eelgrass associated bacteria, refer to NCBI BioProject PRJNA802566 in the Related Datasets section below.