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The potential effects of global climate change on the distribution of native and introduced Zostera seagrasses on the Pacific Coast of North America
Citation:
Shafer, D. AND Jim Kaldy. The potential effects of global climate change on the distribution of native and introduced Zostera seagrasses on the Pacific Coast of North America. Presented at Environmental Adaptation and Speciation of Plants and Fungi, October 07 - 08, 2012.
Impact/Purpose:
At least two seagrass species in the genus Zostera occur on the Pacific coast of North America: the native species Zostera marina L., and an introduced species, Z. japonica Ascher. & Graeb. Z. marina occurs along the entire Pacific coast of the United States and Canada. Through collaborative research we have conducted experiments to evaluate the physiological response of these seagrasses to variations in temperature and light. Our data suggests that both species may respond to future environmental conditions and that the non-native species is likely to continue to expand its distribution. The ecological consequences of these ecosystem alterations are poorly understood.
Description:
At least two seagrass species in the genus Zostera occur on the Pacific coast of North America: the native species Zostera marina L., and an introduced species, Z. japonica Ascher. & Graeb. Z. marina occurs along the entire Pacific coast of the United States and Canada. Zostera japonica was first reported along the Pacific Coast of North America in 1957 and is thought to have been introduced along with oyster seed stock imported from Japan. For more than fifty years, distribution of Z. japonica was limited to southern Oregon and Washington, USA, and southern British Columbia, Canada. Within the last decade, Z. japonica has expanded its latitudinal range both northward and southward. Where these two Zostera species co-occurr, they typically occupy separate zones, with Z. marina occupying the lower intertidal and shallow subtidal zones, and Z. japonica occupying the mid- to upper intertidal. Although competitive interactions with Z. marina play a role in determining the boundary between the lower limit of Z. japonica and the upper limit of Z. marina where both species co-exist, Z. japonica remains limited to the upper and mid-intertidal zones even in the absence of Z. marina at its lower boundary, suggesting that interspecific competition does not control the lower limit of Z. japonica zonation. The mid- to upper intertidal zonation of Z. japonica can not be explained by a higher desiccation tolerance. Preliminary data (unpublished) also suggest that Z. japonica should be physiologically capable of growing at depths similar to that of Z. marina; therefore light limitation is unlikely to control the lower limits of Z. japonica zonation. Since zonation patterns can not be explained by interspecific competition, differences in desiccation tolerances, or light requirements, differences in their thermal optima may be responsible for the observed zonation patterns of these two species in the intertidal and shallow subtidal zones. The optimum growth temperatur