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Effects of microtopographic variation and macroalgal cover on morphometrics and survival of the annual form of eelgrass (Zostera marina)
Citation:
Nelson, Walt AND G. Sullivan. Effects of microtopographic variation and macroalgal cover on morphometrics and survival of the annual form of eelgrass (Zostera marina). AQUATIC BOTANY. Elsevier Science Ltd, New York, NY, 145:37-44, (2018).
Impact/Purpose:
Eelgrass provides important food, shelter, and nursery habitat for many important estuarine species. In the face of large-scale losses of seagrass from human activity around the globe, study of the conditions leading to success of eelgrass restoration, including intertidal populations, has become increasingly important. Emeritus Scientist Walt Nelson and National Research Council post-doctoral associate Gary Sullivan of EPA-WED conducted a study of recruitment and survival of seedlings of eelgrass on an intertidal sand flat in Yaquina Bay, Or, and found that survival, growth and seed output was significantly lower in areas that were only several centimeters higher that the surrounding sand flat. Blooms of green macroalgae also tended to accumulate more densely and more rapidly on the same elevated areas. Through shading and production of potentially toxic hydrogen sulfide from decomposition, macroalgal mats were closely correlated with the impacts to seagrass observed. The study concluded that while difference in desiccation stress may have played some role in determining the influence of small scale elevation differences on eelgrass seedling success, macroalgal effects appear to be predominant. The results point to approaches to achieve better success in eelgrass restoration efforts in the Pacific Northwest region.
Description:
A disjunct population of the annual form of the seagrass Zostera marina that occurred in the upper intertidal zone of Yaquina Bay, Oregon was sampled to determine whether there were differences in recruitment, growth, survivorship and morphology associated with microtopographic location on the sand flat. Population responses of seagrass found in areas differing by only a few cm in vertical elevation were compared. There was higher abundance, greater survivorship, and higher number of shoots per plant in microtopographic low areas. Plants in lower areas also had significantly longer shoots, greater total above ground biomass, greater biomass per shoot, and greater biomass of reproductive spathes than plants growing in immediately adjacent microtopographic high areas. Green macroalgal cover was higher and accumulated more rapidly in microtopographic high areas as compared to low areas, and both spatially and temporally was correlated with decreased recruitment and increased mortality in these slightly elevated areas. While impacts of desiccation may have played some role in determining the influence of microtopographic variation on the annual Z. marina population, macroalgal effects appear to be predominant.
