You are here:
NATURAL FACTORS CONTROLLING INTERTIDAL EELGRASS: IS T17THHIS AS HIGH AS WE CAN GET?
Citation:
Boese, B L. AND B. D. Robbins. NATURAL FACTORS CONTROLLING INTERTIDAL EELGRASS: IS T17THHIS AS HIGH AS WE CAN GET? Presented at 17th Biennial Estuarine Research Federation Conference, Seattle, WA, September 14-18, 2003.
Description:
Eelgrass (Zostera marina) in many open-coast Pacific Northwest estuaries is primarily intertidal, yet little research has been done on the natural factors which control its upper intertidal growth boundary. In Dec. 2002 a two year study was completed in Yaquina Bay (Newport, OR) to evaluate the effects of light, macroalgae, erosion, and aerial desiccation on Z. marina biomass, density and morphology. Study sites were located at six locations, three on steep and three on shallow bathymetric slopes, within the principal Yaquina Bay eelgrass meadows. At each site, triplicate plots (9m2) were placed at six tide heights which ranged from the middle of the permanent meadow (perennials) through the transition zone (annuals and perennials) to a high intertidal zone (annual shoots). These plots were sampled monthly for shoot location and type (vegetative, reproductive, seedling). Canopy height, algal biomass and exposed rhizomes were also noted. Light along the tide gradient was measured continuously at one of the sites. Six measurements of growth rate were made during the study. Results suggest that light is not limiting in the transition zone. Although erosion may be important in determining the lower limit of Z. marina at steeply sloped sites, it is probably not important in determining the upper limit. Algal biomass peaks in Sept/Oct, which corresponds to a period of decline in Z. marina shoot density, with a winter increase in shoot numbers observed immediately after algal volume decreases. Desiccation damage is greatest in high intertidal shoots resulting in broken blades which may be related to shorter canopy height.