For estimation of biomass, quadrant method is reliable and convenient in the intertidal rocky surfaces.Depending upon the abundance of algae, use the size of the quadrant (25X25 CM or 50x50 CM ). If you want to estimate the biomass of only Gigartina acicularis, then use 25X25CM quadrant and again it subdivide into 5x5 CM blocks. Now you can collect the biomass of only above said sps from each block , after drying the material, measure the weight of the material.