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

Body size is a basic animal feature that defines its functioning in multispecies assemblages. Polychaetes are numerically dominant components of marine macrobenthos, playing a key role in benthic productivity. They are also the most problematic group regarding body-size assessments due to common fragmentation of fragile bodies during sample processing that inhibits direct assessments of their size and biomass. Here, we present quantified 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-fitted regression equations (p < 0.001, r from 0.41 to 0.99) were selected for 28 polychaete families, six orders, two infraclasses, and one subclass based on the measurements on 3580 complete individuals collected in the North Atlantic (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, specific formula was proposed. The method has been applied to assess the size spectra of macrozoobenthos based on 18 van Veen grab samples collected at six stations in two Spitsbergen fjords. The percentage contribution of complete individuals in polychaete biomass and abundance in size classes varied between 0% and 43%, with the lowest percentages noted in two dominant families-Cirratulidae and Lumbrineridae. The presented method is likely to be widely applied in studies requiring polychaete individual size assessments (e.g., benthic biomass size spectra, population dynamics, and secondary production).