Methodological considerations on the coastal and transitional benthic indicators proposed for the Water Framework Directive

A large data set from the coastal environment of the Mediterranean across benthic enrichment gradients was used to test the performance of various indices as indicators of the seabed environmental conditions. Comparisons involved samples sieved through different mesh sizes, taken in different seasons and taken with different samplers. Most indices were found not to be affected by sieve mesh size, they showed some variations with sampling season and they varied considerably with sampler (sampling size) used, but also they were found to be significantly intercorrelated. Among the indicators tested, the Benthic Quality Index at the family level (BQI-family) was found to be the least sensitive in changes in the sampling configuration; it is highly correlated with all the other indicators and needs less time and taxonomic expertise. Our results indicate that there is a need for standardization of the methodology used during sampling for the Water Framework Directive, since the sampling configuration (and the indicator used) may to a large extend determine the results of the Ecological Status (ES) analysis.