Application of an Objective Method for Detecting Changes in Fish Communities: Samar Sea, Philippines

Abstract

Changes in ecological communities are often measured by the use of diversity or indices. Although many indices are available, their statistical properties are usually unknown and significance cannot be assigned to the value of a similarity index or to the difference between two values of a diversity index. FAUNSIM is a nonparametric method for determining the statistical significance of differences between two species assemblages for which no replicate samples are available. It makes use of Monte Carlo simulation and knowledge of the pool of species that may be found in the general region of interest. It generates an approximate probability distribution for the number-of species expected to be common to the two 888emblages of interest. This method was applied to trawl survey data from Samar Sea, the Philippines. Using FAUNSIM, significant differences in the assemblages of demersal fish were found in both time and space. Deep and shallow stations were occupied by distinct assemblages. Assemblages at some stations changed significantly froml979 to 1980. Visual inspection of changes in assemblages and standard diversity indices were not as effective as FAUNSIM in assessing the significance of observed changes in ecological communities.