| The nonindigenous seagrass Zostera japonica is found along the eastern Pacific coast from southern British Columbia, Canada, to Humboldt Bay, California. Within this range, variation in life history strategy, flowering frequency and intensity, and allocation of plant resources along a latitudinal gradient from north to south is evidence of a climate effect. Although climate is known to have a strong influence on the distribution of plants, this study is the first to investigate the potential role of climate in the distribution of an introduced marine plant. This research focuses on a comparison of the physiological responses of two populations of Z. japonica, located near the current northern and southern range limits in North America, to two particular aspects of climate, water availability (i.e. desiccation) and temperature.; Photosynthesis and growth of populations near the limits of the species' range exhibited different temperature responses. The southern population was better adapted to high temperatures, making further expansion of Z. japonica along the California coast likely. Both physical (e.g., tides and currents) and biological (e.g., migratory waterfowl) transport processes may be involved. Due to changes in climate, expanding populations will be exposed to both increased temperatures and desiccation potential. As a result, the position of Z. japonica within the intertidal zone may be shifted lower to escape the combined effects of increased temperature and desiccation during periods of emergence. This could lead to increasing overlap and competition with the native eelgrass, Z. marina.; At the present time, conflicting management approaches to the presence of this species suggests there is little consensus among resource managers regarding the status of this species. While introduced species are generally thought to have a negative effect on native ecosystems, this species does provide a positive habitat benefit for migratory waterfowl populations. Our understanding of the effects of this species on other nearshore ecosystem functions is limited. Additional data would contribute to the development of appropriate management strategies. |
