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Abstract: Length–mass relationships are potentially useful tools to estimate individual biomass, assuming a relative invariance within and among populations and, sometimes, among species pertaining to a same family or order. Here, we present a field test of these assumptions in guilds of benthic macroinvertebrates colonising transitional water ecosystems. To this aim, we are analysing length–mass relationships of benthic macroinvertebrates of transitional water ecosystems and assessing their variability among populations of a same species and among species of a same family and/or order. Data are from synoptic studies carried out at four oligohaline transitional water ecosystems, from the Southern Italy and the Danube delta ecoregions; they refer to 40 macroinvertebrate taxa selected from the overall species pool according to absolute and relative density requirements. Species composition differed widely among ecoregions while length–mass relationships of the species occurring in both ecoregions did not; the variability of length–mass parameters of these species among ecosystems was lower than 10%. Length–mass regressions were relatively conservative also with respect to taxonomic resolution; significant differences were observed among species within 5 out of the 7 orders tested but differences in slopes and intercepts were on average lower than 15%. Therefore, our results, representing one of the first efforts to catalogue length–mass relationships for benthic macroinvertebrates in transitional waters, support the assumption of relative invariance of length–mass relationships and their use in studies where gross estimates of population biomasses are required. [Copyright &y& Elsevier]

Benthic macrophyte communities of different substratum types (soft, hard) were studied in eleven differently impacted sites belonging in two different water typologies (transitional waters: Lesina Lagoon, Varna Lake; coastal waters: Varna Bay) and two ecoregions (Mediterranean Sea, Black Sea). Species lists were compiled for each study site, 20 taxa were found at Lesina and Varna Lake and Bay, and the abundance of each taxon was determined at each site. The relationship between nine metrics related to community structure [species richness, % of total coverage, dry biomass (g/m), and cluster and multi-dimensional scaling plot of Bray-Curtis similarity] and function [Ecological Status Group I % coverage, ESG II % coverage, Ecological Evaluation Index (EEI-c) and Ecological Index (EI)] and key abiotic factors and an anthropogenic stress index (EnII) were studied. A strong relationship (Spearman rank correlation coefficient ρ ≤ −0.89; R ≥ 0.89) between anthropogenic stress and functional indices, EEI-c and EI, was found. The structural index 'species richness' correlated negatively with EnII and positively with salinity, demonstrating a freshwater and confinement influence on species diversity. EEI-c and EI indices classified the studied sites and locations in different Ecological Status Classes in accordance with the anthropogenic stress gradient. [ABSTRACT FROM AUTHOR]

Abstract: Size spectra show common patterns of variation among ecosystem types, functional guilds and taxonomic groups, as well as predictable responses to pressures. Here, we extend the size spectra approach to macroinvertebrate ecological status assessment in transitional waters, by developing, testing and validating a multi-metric index of size spectra sensitivity (ISS), which integrates size structure metrics with metrics describing the sensitivity of size classes to anthropogenic disturbance and species richness measures. The ability of different theoretical models of size spectra sensitivity to discriminate between undisturbed and disturbed ecosystems and levels of environmental stress was evaluated. We have used data on benthic macroinvertebrates within 12 Mediterranean and Black Sea transitional water bodies (i.e. coastal lagoons) from Italy, Albania, Greece, Bulgaria and Romania and compared the models’ efficiency through their pressure-impact response along organic load and enrichment gradients. Data from a thirteenth Mediterranean lagoon was used for validation purposes. Asymmetric models of size class sensitivity, assuming higher sensitivity of larger body size classes, were found to be more effective than symmetric models, with higher sensitivity of less common size classes, in distinguishing undisturbed from disturbed lagoons and lagoon stations. The ISS based on the asymmetric sensitivity model that was most efficient in identifying the anthropogenic impacts also showed significant dose–response relationships along environmental parameters describing the organic load and enrichment gradients. A scheme for the classification of Ecological Quality Status based on the macroinvertebrate ISS is proposed and validated. The validation procedure found that ISS is an effective and sensitive monitoring tool, easy to apply and to inter-calibrate among laboratories. Moreover, the tests performed here over a very large ecoregional area have proved the spatial robustness of the new index. [Copyright &y& Elsevier]