The seagrasses Zostera marina and Zostera japonica coexist along a portion of a gradual intertidal gradient at Roberts Bank, British Columbia. Individual comparisons of 11 morphological and 2 population characters for Z. marina did not reveal consistently significant differences between the deeper water monospecific population and the population in mixed vegetation. Similar comparisons between the shallow-water monospecific Z. japonica and the mixed vegetation indicated a suppression of Z. japonica shoot production (density) under a canopy of Z. marina. Principal components analysis was used to summarize the original data into a new set of multivariate characters that were then compared using ANOVA and MANOVA. With these analyses, the subtle differences between Z. marina populations became significant at various times. Similar analyses for Z. japonica indicated that morphological differences between the monospecific and mixed populations persisted throughout the sample period. The multivariate characters provide summaries of populations that are useful in detecting subtle responses to varied environments. Key words: Zostera marina, Zostera japonica, seagrass morphology, multivariate analysis, MANOVA, intertidal zone.