Efficiency Estimates for Various Quadrat Sizes Used in Benthic Sampling

Abstract

A review of some of the marine littoral ecological literature revealed that area sampling is frequently used to assess biomass and both species densities and associations. The 3 most common sample unit configurations were the quadrat, circle and rectangle; their popularity was 66.7, 19.0 and 14.3%, respectively. The percentage of researchers using areas of < 0.25, 0.25, 1.0 and > 1.0 m2 was 42.9, 23.8, 28.6 and 4.8%, respectively; their reasons for using these areas were not stated. This sampling study was designed to determine the efficiency of 6 sample unit sizes (0.25, 1.0, 1.56, 2.25, 2.99 and 4.0 m2) when assessing macrophyte biomass. The cost in time to harvest a fixed sample of 20 m2 varied markedly with sample unit size, as did sampling precision. The rates of harvest 1 m2 with the 2.25 and 0.25 m2 quadrats were 9.1 and 34.8 min, respectively; the respective sampling precisions (CV [coefficient of variation]) were 0.176 and 0.075. The formula n = [S/(.hivin.X .cntdot. CV)]2 was used to determine sample unit number for a given precision of the estimate (CV''s = 0.075, 0.10 and 0.15). The cost in time to attain a sampling precision of 0.10 for the 0.25 and 2.25 m2 sampling units was estimated at 393.2 and 569.9 min, respectively. A large number of small sample units (0.25 m2) was more efficient than a smaller number of large sample units (4.0 m2). Sampling efficiency should be determined prior to the initiation of an area sampling program.