The performance of biomass-based AMBI in lagoonal ecosystems

• The performance of biomass-based AMBI was assessed in transitional ecosystems.
• Data transformation was used to down-weight the importance of dominant taxa.
• The relative importance of ecological groups changed when using abundance or biomass.
• Good agreement was found between all AMBI-based indices and disturbance.
• Severity of transformation had a role on correlation with environmental factors.

We studied the performance of the AZTI Marine Biotic Index AMBI manipulating input data collected from lagoonal ecosystems. Our data set consisted of macrofaunal abundance and biomass counts gathered at a variety of sites at which the disturbance status was known. Input data were also manipulated using a set of transformations of increasing severity. Biotic indices were calculated using raw and transformed abundance, biomass and production. Among the three categories of AMBI-based indices, medium transformation of data gave the highest correlation with pressures. However, increasing the severity of transformation generally resulted in a decrease of the correlation with environmental factors. The relative importance of ecological groups changed when using abundance or biomass, sometimes leading to an improved ecological status classification. Being biomass and production more ecologically relevant than abundance, using them to derive AMBI-based new indices seems intriguing, at least in lagoonal waters, where the community is naturally disturbed and dominated by opportunists.