A subset of at least 5 images (out of 10 to 30) was selected for analysis from each site during each year. These images were included based on focus quality, as barnacles outside the focal plane could not be identified. Because of variation in the flatness of the underlying rock, the size of the available space in focus in each image varied; the countable area ranged from 5 to 155 cm2 , with a mean quadrat size of 32.4 cm2 . Images were imported into the open-source software ImageJ (Abramoff et al. 2004) for subsequent analysis. Semibalanus balanoides individuals were identified based on plate number and shape as described by Southward & Crisp (1963). Differentiation of S. balanoides from other common intertidal species in the region, including Chthmalus stellatus, C. montagui, and Elminus modestus, is relatively straightforward, as S. balanoides has a diamond shaped operculum and 2 of its 6 shell plates are much narrower than the others (Southward 1976). Individuals were assigned to 3 age classes: young of the year (YOY) 1-year olds and older adults. YOY are readily recognized by having white plates that are well defined, whereas adults are more stained and brown in color and typically have significant fusion and weathering of the plates. The metric tape in each of the photographic quadrats was used to calibrate the ImageJ measurement tool, which was subsequently used to calculate the average density of S. balanoides individuals of each age class at each site.
BCO-DMO Processing:
- added conventional header with dataset name, PI name, version date, reference information
- renamed parameters to BCO-DMO standard
- reformatted date from d-Mon-yy to yyyy-mm-dd
- longitude-180 calculated from lon-360
- replaced blank cells with 'nd'
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