Biotic indices for ecological status of transitional water ecosystems

1 - The biological elements, proposed by the WFD as quality elements for the classification of ecological status of the transitional waters are: composition, abundance and biomass of phytoplankton; composition and abundance of other aquatic flora (i.e. macroalgae and angiosperms); composition and abundance of benthic invertebrate fauna; composition and abundance of fish fauna. 2 - Although the directive proposed these biological elements, it doesn’t provide clear indication on the “biocriteria” to achieve. WFD suggested that ecosystem health should be defined by comparison to reference conditions. 3 - Recently, there has been a growing interest and need for sound and robust ecological indices to evaluate transitional ecosystem status and condition, mainly under the scope of the Water Framework Directive implementation. 4 - A good biotic index should reflect the biological integrity; respond to environmental stresses in monotonic way; be measurable with low error; be cost-effective; be not invasive (i.e. the measure methods do not significantly disturb or alter habitats and biota). 5 - Several indices have been developed for environmental quality assessment using macrobenthic assemblages, ranging from the comparison of a single metric to complex multivariate analyses. Some indices were developed for fish assemblages and for macrophytes, but only few indices were proposed considering the phytoplankton. 6 - In this report, we shown and compare several biotic indices used for evaluating ecological status of transitional water ecosystems using the five biological quality elements.