Estimating the abundance of benthic invertebrates:a comparison of procedures and variability between observers

Different procedures for underwater sampling of epifaunal organisms were compared for their robustness to bias due to observers and precision using multifactonal sampling designs. Variability among 3 observers was tested in relation to: (1) the method employed to estimate the percent cover of organisms (visual vs point-intercept technique); (2) the size of quadrats (50 X 50 vs 20 X 20 cm);