RAHarCalc: a geometric image-based software for morphology-based biomass estimation of harpacticoid copepods

Accurate estimation of individual biomass is fundamental for quantifying production, trophic transfer, and functional structure of meiofaunal communities. Harpacticoid copepods, among the most abundant metazoans in marine sediments, exhibit pronounced interspecific and functional variation in body shape that challenges traditional length–weight and simple biovolume models. We present RAHarCalc, a Python-based image-assisted geometric software that reconstructs organismal volume from multi-view microscopy outlines using analytically defined primitives (ellipsoids, frusta, and cones) and converts volume to wet biomass via density and correction factors. The method was evaluated using 120 adult and late copepodite harpacticoids from the continental shelf off Cochin (eastern Arabian Sea), representing six families and contrasting morphotypes. Validation against pilot CLSM reconstructions demonstrated a mean absolute error (MAE) of less than 3–5%, whereas conventional length-weight regressions (LWRs) showed errors of approximately 4–8%. Reproducibility between operators (coefficient of variation (CV) below 5%) and a two – to three-fold increase in processing speed relative to ImageJ workflows indicate that RAHarCalc provides a practical, non-destructive and morphologically explicit framework for harpacticoid biomass estimation in ecological studies.