Development of a new index for the assessment of hydromorphological alterations of the Mediterranean rocky shore

Abstract

The assessment of the status of coastal waters is required by the European Water Framework Directive. The aim of the present study was to test the response of benthic invertebrates to hydromorphological (HM) alterations and to develop a new index for the assessment of HM alterations of the rocky shore, based on benthic invertebrates. Fifty samples were collected, 10 from pre-classified HM classes 1, 3, 5; 15 from class 2, and 5 from class 4. Seven HM variables describing habitat conditions were used to test the benthic invertebrate response and to develop the HM stressor gradient: material, texture, structure, belt length, sedimentation, water retention and artificially induced mobility. Abundance, some diversity (Shannon–Wiener, Simpson's and Evenness) and richness (number of taxa) metrics showed low correlation values ( r < 0.5) against HM variables and HM stressor gradient, indicating that tested metrics have limited value in assessment of the HM degradation impact on coastal benthic invertebrates. On the other hand, significant differences in the structure of benthic invertebrate assemblages among HM classes were observed (One-way ANOSIM global test r = 0.53, P < 0.0001). In the partial canonical correspondence analyses each of seven HM variables statistically significantly ( P < 0.05) explained individual portion of the benthic invertebrate taxa variability. HM indicative values ranging from 1 to 9 were defined for each of 229 taxa, according to its distribution along the five HM classes. HM indicative weights ( WHM) between 1 and 5 were defined according to the valences distribution among HM classes. HM indicative values, WHM and log 5 abundance classes were combined in a new Benthic Index for Rocky Shore (BIRS), using the weighted average approach. The combination of all three parameters in the BIRS showed a statistically significant ( P < 0.05) response of the new developed index to HM stressor gradient, with a high Pearson correlation coefficient ( r = 0.97). Further work has to be done in order to develop a WFD compliant method with five classes’ boundary values. Nevertheless, the new developed index has a good potential to contribute to existing coastal assessment systems. Especially, as impact of hydromorphological alterations on coastal communities was almost neglected so far, despite being one of the main threats to coastal water integrity.