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 three 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. My sampling study was designed to determine the efficiency of six 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 to 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) were 0.176 and 0.075. The formula [Formula: see text] 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). I recommend that sampling efficiency be determined prior to the initiation of an area sampling program.