A RAPID METHOD FOR ESTIMATING BIOMASS SIZE SPECTRA OF BENTHIC METAZOAN COMMUNITIES

The construction of biomass size spectra in aquatic environments suffe rs from two main problems: (i) it is a labour-intensive process, and ( ii) there is a lack of conformity in methodologies. This study evaluat es a technique that produces biomass spectra for benthic metazoans fro m subsamples stratified using a geometric series of nested sieves. The technique was applied to metazoan communities from three sites, two f reshwater and one brackish water, on a small rivet in southern Britain . Random subsamples of animals from each sieve size were measured usin g image analysis and showed significant differences in body size, as e quivalent spherical diameter (ESD), among all but two sieves. There wa s no significant difference in ESD among sites. Despite the propensity for long thin animals to pass lengthwise through meshes, sieves conta ined a consistent range of individual body sizes. Mean individual body size and abundance data for each sieve were used to calculate total b iomass. These size spectra were consistent with those from previous st udies, and it is hoped that this method will encourage the wider appli cation and more rigorous measurement of biomass size spectra in aquati c ecology.