ON REPLICATES FOR COMPARING SPECIES DENSITIES IN SPACE AND TIME

Because benthic foraminifera exhibit spatial heterogeneity, a number of replicates or multiple biological samples are necessary to estimate precisely population densities. In this study, we examine the efficacy of taking 4 or fewer replicates to differentiate among mean densities in space and time. For space, 4 stations along a traverse with 4 replicates per station were compared with ANOVA within Mission Bay, Texas using the 4 most abundant species. Four replicates per station resulted in a significant difference in mean densities among stations for 3 of 4 taxa, 3 replicates distinguished 2 of 4, and neither 2 or 1 detected differences. For time, a single station was sampled in the Indian River Lagoon, Florida seasonally for 4 years. Either 4 or 3 replicates were found to separate mean densities among the 4 years for 3 of 4 taxa, whereas 2 or 1 replicate could not detect any difference in mean densities among the 4 years. Based on these and previous results we recommend at least 4 replicates per station for environmental monitoring. However, for larger ecological entities such as biofacies, 1 sample at each station along a single traverse containing 4 stations in each bay could delineate Mission, Copano and Mesquite Bays in Texas.