Uncertainty of macroinvertebrate body-sizes derived by length per weight relationships, taxonomic sufficiency and influence on the ISS ecological indicator: a study case in Lesina lagoon (Mediterranean Ecoregion, Italy)

Indicators based on body-size metrics have been recently developed and applied. Despite of the implication of body-size in ecological status assessment, the determination individual biomass of benthic macroinvertebrates (BM) is a complicate, time-consuming, time-lag, and expensive procedure. They are the greater limitation in the application of body-size based indicators, specifically for the new multi-metric Index of Size Spectra (ISS). The aim of the research was to test simplifying procedures for a more user-friendly application of body-size based indicators in transitional waters. The research was performed in the Lesina lagoon (Mediterranean ecoregion, Italy). We evaluated the uncertainty of estimating the individual biomass (IB) of BM applying the length per weight relationships (LWRs), obtained at species and order level. Than we compared the ISS using: 1. direct measures of IB of site/sampled BM; 2. indirect measures of IB obtained by LWRs at species and order taxonomic levels; 3. indirect measures of IB obtained by LWRs of a previous dataset realized in Lesina; 4. indirect measures of IB obtained by LWRs at species and order levels of a previous dataset realized in different sites. The accuracy of body-size spectra and ISS achieved with the different direct and indirect measures of individual biomass will be described and compared in the light of developing simple, rapid and accurate biomonitoring tools for the ecological assessment of transitional waters.