Researchers generally use only one type of plant or animal to study a particular marsh. Consequently, it has been impossible to directly compare zonations obtained using different groups between sites. To facilitate such comparison, cluster analysis of foraminiferal, diatom, and macrophyte data collected in transects from a tidal marsh at Zeballos, northwestern Vancouver Island, British Columbia, was carried out. These analyses yielded three, six, and four mostly elevation-controlled assemblage zones, respectively. Physical parameters such as salinity and oxygen concentration affect the various taxa differently, resulting in significantly different assemblage boundaries between groups. A composite analysis of all groups yielded an assemblage zonation very similar to that obtained with the macrophytes alone. Although fewer assemblage zones were resolved with the composite analysis than with the diatom data alone, fewer sample misclassifications resulted in more precise elevation determinations. A second composite analysis using only foraminiferal and diatom data, which is more useful to paleo-sea level researchers, also gave four elevation controlled assemblage zones, although assemblage zone elevational boundaries differed slightly from those obtained with data from all groups. Our results will permit researchers working on diatoms, foraminifera or macrophytes to calibrate their zonations thus making it easier for workers in different fields to compare their results.