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  • Uncertainty of phytoplankton indicators with respect to sample-size: a case study on a large transitional water dataset (WISER)
    Cozzoli, Francesco ...
    Phytoplankton is a key element for the assessment of ecological and environmental status of aquatic ecosystems. The methods used to sample phytoplankton communities are based on cell counts, ... determining a trade-off between the number of cells counted and the number of phytoplankton samples in a monitoring plan, whenever the financial budget, the available personnel or the response time are limited. We investigated the optimal sample size effort, intended as number of phytoplankton cells counted per sampling station, of many commonly used metrics. To this aim, precision and uncertainty of the metrics as a function of sample size have been addressed using a case study carried out in the Lesina lagoon (Apulia, Italy), where 12000 cells have been counted per sample within five sampling stations. Overall, we show that some of the commonly used indices/metrics for the description of phytoplankton communities are strongly dependent upon the sampling effort (as number of counted cells per sample), while other metrics are relatively independent. Metrics based on the number of taxa only (e.g. Taxonomic richness) or on the ratio between number of taxa and number of individuals (e.g. Margalef's diversity index) or on the species evenness (e.g. Pielou's evenness index) strongly depend on the sample size and their uncertainty (in term of sampling variance), which is usually large on small samples. Some other metrics [metrics of taxonomic diversity accounting for the proportional abundance of each taxa (e.g. Shannon-Wiener's diversity index); metrics accounting for the dominance of the most abundant taxa (e.g. Hulburt dominance index); metrics derived from the individual size distribution (e.g. Inter-decile range, ISS Phyto)] are able to achieve high precision and low uncertainty at small sample sizes (virtually less than 50 counted cells) and thus they maximize the ratio between allocated effort and gained information. The investigated relationships can be used as a guideline to interpret the response of different datasets and provide recommendations about the optimal effort per sample to be allocated in phytoplankton monitoring plans.
    Vir: Abstract book [Elektronski vir] (Str. 128)
    Vrsta gradiva - prispevek na konferenci
    Leto - 2017
    Jezik - angleški
    COBISS.SI-ID - 4451151

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