AN EVALUATION OF A RAPID VISUAL TECHNIQUE FOR ESTIMATING SEAGRASS BIOMASS

A visual census technique for estimating seagrass biomass has been adapted from a comparative pasture yield method. The above-ground biomass of seagrass within sampling quadrats was ranked with respect to a set of reference quadrats which were preselected to provide a scale of standing crop dry weights. At the end of each sampling period, sufficient quadrats were harvested to calibrate the scale. Using this method, monthly mean standing crops were estimated from May 1987 to April 1988 for a multispecific seagrass bed on Green Island, North Queensland. Values obtained ranged between 61.52 and 113.08 g dry weight m-2. The precision (SE/xBAR) of each monthly estimate ranged from 0.05 to 0.13, a satisfactory level for field programs. This method is more precise and time efficient, and is less destructive than some traditional harvesting methods.