Reproduction and adaptation in eastern Pacific eelgrass populations

Zostera marina meadows frequently overlap tidal habitats in which different environmental conditions are found. The amount of clonal or sexual reproduction may reflect the level of disturbance found in the habitat. Also, timing of anthesis or stigma receptivity by intertidal eelgrass to coincide with low tides may increase pollination efficiency. How is reproduction in Z. marina influenced by tidal activity? This thesis addresses this question from three different perspectives: the effect of physical habitat on intra-population structure; the effect of tidal flux on intertidal pollination dynamics; and evidence of varying reproductive strategies among local intertidal and subtidal habitats. Chapter one investigates the population genetics of eelgrass in a habitat with dissected physical structure. Findings indicate that little structure exists between discrete beds, and genetic diversity is not consistent with widespread clonality. This suggests efficient gene flow across channels, likely by many genets. Chapter two examines the influence of tides on the presentation and dispersal of eelgrass pollen. Results suggest that timing of pollination is not coordinated with bi-monthly tidal events, and that a strategy relying on pollen-concentrating low tide would interfere with pollination. Chapter three investigates reproductive strategies of Zostera marina in nine populations. Results suggest that Z. marina reproductive strategy does not differ between habitats. Evidence of reproduction through sex and clonal growth were both found to be scarce. These studies can aid the management of eelgrass populations by discouraging the assumptions of low genetic diversity and little sexual reproduction. Intertidal habitats do not appear to closely follow many of the hypotheses generally applied to them.