The proportion of life history phases in red seaweeds is an important descriptor of population structure. This paper describes the relative abundance of gametophytes and tetrasporophytes of Mazzaella oregona (Rhodophyta: Gigartinales; formerly M. heterocarpa), focusing particularly on the effects of wave exposure on the proportion of both life history phases. In two different rocky points in Barkley Sound (Pacific Canada), gametophytes were, in proportion to tetrasporophytes, relatively more abundant under low wave exposure than under high wave exposure in July 2002, during the period of highest abundance for this species. The inverse relationship between the G:T ratio and the degree of wave exposure also occurs for local M. splendens, but not for local M. parksii. Differences in frond size and population density between these three sympatric species are related to the effects of wave exposure on their G:T ratio.