%0 Journal Article
%T Getting to the Point: Accuracy of Point Count in Monitoring Ecosystem Change
%A Eric Pante
%A Phillip Dustan
%J Journal of Marine Biology
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/802875
%X Ecological monitoring programs depend on the robust estimation of descriptive parameters. Percent cover, gleaned from transects sampled with video imagery, is a popular benthic ecology descriptor often estimated using point counting, an image-based method for identifying substrate types beneath random points. We tested the hypothesis that the number of points needed to robustly estimate benthic cover in video imagery transects depends on cover itself, predicting that lower cover will require more points/frame to be accurately estimated. While this point may seem obvious to the statistically inclined, the justification of point density has been largely ignored in the literature. We examined the statistical behavior of point count estimates using computer-simulated 20£¿m-long transects patterned after data from a Bahamian reef. The minimum number of points necessary to insure accurate percent cover estimation, the Optimal Point Count (OPC), is a function of mean percent cover and spatial heterogeneity of the benthic community. More points are required to characterize reefs with lower cover and more homogeneously distributed coral colonies. These results show that careful consideration must be given to sampling design and data analysis prior to attempting to estimate benthic cover, especially in the context of long-term monitoring of degrading coral reef ecosystems. 1. Introduction A common problem while working in ecological characterization and monitoring programs is how to effectively test and optimize methods and experimental designs. Live percent cover is a widely used ecological descriptor in marine conservation biology and large-scale monitoring projects (e.g., [1¨C4]) and has been a key parameter in the quantification of coral reef degradation over large spatial scales (e.g., [5¨C7]). Using point count to analyze video transects and photoquadrats is an efficient way to estimate percent cover and monitor large areas, because it allows copious amounts of data to be collected while minimizing underwater time, and provides a permanent record of the benthic community [8, 9]. Substrate types underlying randomly assigned points are identified. Percent cover is then estimated as a ratio of the number of points overlaying a substrate type to the total number of points. The number of points to be used per unit area (point density and the unit area being an image frame from a video transect) is crucial to obtaining a robust estimate of percent cover, and initial statistical tests should be performed to establish the point density that will provide adequate
%U http://www.hindawi.com/journals/jmb/2012/802875/