A method for measuring the size of early euphausiid larvae

Abstract

A simple method to measure early euphausiid larvae is tested on 35 specimens of Euphausia superba obtained in the Weddell-Scotia Confluence region (ranging from Calyptopes I to Furcilia III) against the measures obtained on the same specimens with a graduated eyepiece.The arrangement of the test includes two observers, four magnifications (from 7.59 to 62.59) whenever feasible and two replications of each measurement. A total of 953 measurements were analyzed in an incomplete random blocks ANOVA design not finding significant differencesbetween magnifications, methods, observers and their interactions. It was found that the relative differences between methods were of the same magnitude as the differences between replications (approximately 5%). The proposed method is less demanding on laboratory work, thus allowing the measurement of the large number of specimens needed to estimate size frequency distributions.