Size assessment in polychaete worms-application of morphometric correlations for common North Atlantic taxa.

Abstract

Body size is a basic animal feature that defines its functioning in multispecies assemblages. Polychaetes arenumerically dominant components of marine macrobenthos, playing a key role in benthic productivity. Theyare also the most problematic group regarding body-size assessments due to common fragmentation of fragilebodies during sample processing that inhibits direct assessments of their size and biomass. Here, we presentquantified relationships that allow an estimation of the total-body length based on morphometric features(widths of thoracic chaetigers) that remain intact after standard macrobenthic sample treatment. The best-fittedregression equations (p< 0.001,rfrom 0.41 to 0.99) were selected for 28 polychaete families, six orders, twoinfraclasses, and one subclass based on the measurements on 3580 complete individuals collected in the NorthAtlantic (Norwegian and Spitsbergen fjords and continental margin). In Capitellidae, Cirratulidae, Oweniidae,and Trichobranchidae, the shapes of the relationships differed among dominant species/genera, and so, specificformula was proposed. The method has been applied to assess the size spectra of macrozoobenthos based on18 van Veen grab samples collected at six stations in two Spitsbergen fjords. The percentage contribution ofcomplete individuals in polychaete biomass and abundance in size classes varied between 0% and 43%, withthe lowest percentages noted in two dominant families—Cirratulidae and Lumbrineridae. The presentedmethod is likely to be widely applied in studies requiring polychaete individual size assessments (e.g., benthicbiomass size spectra, population dynamics, and secondary production).