A Computer Model Study of Zooplankton Patchiness and Its Effects on Sampling Error1

A computer model using estimates of patch structure parameters determined from an ocean study was developed to study the effects of spatial structure on the error of replicate net tows. The precision of nine replicate tows increases with increasing patch size, regardless of the position of the patch centers, and the largest net provides the most precise estimates. Lengthening the tow also results in significant increases in precision (up to a factor of 2), not related directly to increases in the volume of water filtered, but apparently to the increase in the probability of sampling the “right” number of patches. When spatial structure is homogeneous, increasing tow length results in a larger reduction of sampling error than does a corresponding increase in net diameter. In general, better estimates of species proportions are obtained when the numbers of individuals per species are inequitably distributed and the degree of patch overlap is the greatest.