A statistical analysis of the performance of the folsom plankton sample splitter, based upon test observations

Abstract

Summary. The device for splitting a plankton sample into two approximately equal parts consists of a hollow cylindrical drum mounted to turn on a horizontal axis, and a vertical semi-circular septum cemented into place midway between the end walls of the drum. About a quart wilt fill the drum up to the axis. After rotating the drum until the septum is above, the sample is poured in. Then the drum is rotated until the septum splits the sample. Lifting the drum ahd rotating a little more, the two separated samples are drained into containers of convenient shape for emptying and filling. Smaller samples are obtained by emptying one container into the drum. Thus aliquot portions o F approximately 1/2 , 5/4, 1/s , etc. of the original are obtained, and the process is continued until the sample is small enough for counting. In general the sample consists of a number of different kinds of plankters each of which is counted separately. Multiplying each count in the ruth fraction by 2m gives an estimate of the number in the original sample. Each step in the splitting process is subject to random errors and possibly biased errors. Studies of these errors are based upon a series of test runs involving both volume measurements and plankton counts. The samples split were specially chosen to represent different types of plankton communities.The several types tested proved not to influence the results materially.Statistical tests involving distribution of Z 2 and departure from the mean, of left and right portions gave convincing evidence that the errors .were random.Thus, averaging separate counts would be expected to reduce the error. Researches on the magnitude of the error were based upon the law of propagation of errors of a product. Furthermore a study of the difference between the left and right samples as well as other investigations on the different sources of error have been made.

Distribution and life cycle of Calanus chilensis and Centropages brachiatus (Copepoda) in Chilean coastal waters:a GIS approach

“…Males, females and copepodites stage V, were counted using either the whole sample or a fraction of it. The Folsom splitter was used for subsampling (McEwen et al 1954). For the purposes of this paper, we have concentrated our analysis in the adult portion of the populations.…”

Mesopelagic faunal transition across the Subtropical Convergence east of New Zealand

“…Some catches contained up to 2 litres of euphausiids. These were subsampled until numbers were reduced to about 100 specimens using a Folsom Splitter (McEwen et al 1954). Two subsamples from each haul were examined and the relative proportions of each species calculated.…”

Barnacle larvae in ice: Survival, reproduction, and time to postsettlement metamorphosis

“…This ability was tested in three experiments by keeping individuals in frozen seawater for periods ranging from 0.5 to 14 d and then monitoring the settlement and metamorphosis of the thawed samples of larvae. Larvae were collected as above, and the sample was split with a Folsom plankton splitter (McEwen et al 1954) as many times as needed to have at least three replicates per treatment. Each split fraction was randomly assigned to a treatment.…”