NAMBER: A biotic index for assessing the ecological quality of mesophotic biogenic reefs in the northern Adriatic Sea

Abstract

1. The aim of the present study was to propose a biotic index (North Adriatic Mesophotic BiogEnic Reefs, NAMBER) suitable for assessing the ecological quality of the mesophotic biogenic reefs of the northern Adriatic continental shelf based on photographic sampling. 2.At each of the 20 study sites, the degree of bioconstruction (expressed as percentage cover of crustose coralline algae), the α-diversity (expressed as the mean number of taxa), and the degree of sensitivity to human disturbance and climate change (based on literature data and expert judgement) of the benthic assemblages were selected as descriptors and combined in the NAMBER index, using the best values that the three metrics can currently achieve in the studied region as a reference.3. The study highlighted that there was large spatial heterogeneity among reefs and high variability in the ecological quality values obtained by NAMBER, ranging from bad to high. The index indicates that reefs lying furthest from the coast, under substantially lower anthropogenic pressure, have a generally higher status of environmental quality. However, a clear geographical pattern did not emerge, as reefs close together often had different ecological qualities. 4. The NAMBER index, which combines three ecological descriptors, in accordance with the requirements of the European Marine Strategy Framework Directive, represents a specific adaptation to the northern Adriatic Sea of a multimetric index previously developed for the north-western Mediterranean Sea, capitalizing on previous knowledge and research efforts. 5. This multimetric biotic index provides an effective standardized tool for monitoring programmes and environmental impact assessments in the northern Adriatic mesophotic biogenic reefs and lays the foundation for ecosystem-based management and conservation in this basin.

Review of the indexes to assess the ecological quality of coralligenous reefs: towards a unified approach

“…The NAMBER Index (North Adriatic Mesophotic BiogEnic Reefs, Piazzi et al, 2023), draws inspiration from the STAR and ESCA-TA indices, by selecting the metrics and adapting the interpretation scales to the ecological and operational conditions encountered when investigating the mesophotic coralligenous banks in the northern Adriatic Sea. Starting with a close-up photographic sampling strategy, the degree of bioconstruction (expressed as percentage cover of crustose coralline algae), a diversity (expressed as the mean number of taxa), and the degree of sensitivity to human disturbances and climate changes (based on literature data and expert judgement) of the benthic assemblages are combined in the index, in terms of ecological quality ratios (sensu WFD) using as a reference the best values that the three metrics can currently achieve in the studied region.…”