Estimation of sample zooplankton abundance from Folsom splitter sub-samples

Procedures are described for estimating the abundance of eachzooplanklon species in a sample after counting at least twosub-samples from a Folsom splitter. A multinomiai model is assumedfor the splitting process. The method may be summarized as follows:two sub-samples, balanced with respect to the left — rightsplits, are counted. The counts for each species are testedfor homogeneity using a x² test. If the counts are homogeneous,an estimator is given which permits the estimation of the numberof animals in the sample, and the variance of this estimate.If the subsample counts are heterogeneous, it is assumed thatclumping has occurred. A procedure is described in which additionalsub-samples are counted to locate the clump, and estimatorsof abundance (and variance estimators) are derived. If the splitterbias is <5%, bias of the abundance estimator is negligiblecompared to the binomial sampling error. Comparisons of speciesabundance between plankton samples is made more rigorous usingthe estimates of mean abundance, and the variance of this mean,provided by the methods described here. ^*Present address: Dunoon Road, Dorroughby, NSW 2480, Australia.