Regional indices of biotic integrity outperform salinity-based and coastwide indices for tidal streams

Human activities have degraded tidal streams by changing the surrounding land, altering freshwater inflows, and reducing water quality. This degradation has affected the faunal communities inhabiting tidal streams. Indices of biotic integrity (IBIs) integrate biological information into water body assessments, but previously developed coastwide IBIs for Texas streams performed poorly in distinguishing degraded from reference sites. The Texas coast exhibits distinct regional differences in climate, inflow, and salinity that likely limit the effectiveness of coastwide approaches. We developed and tested new nekton and benthic IBIs structured by both regional and salinity-based classifications and evaluated their performance with collected and independent (acquired) datasets. Collected data was based on consistent sampling methodologies, whereas acquired data was based on several different methodologies. IBIs of all classification systems exceeded 50% efficacy when used with collected data, but only the regional benthic IBIs maintained >50% efficacy when used with acquired data. Regional refinement within Texas' climate gradient improved performance more consistently than salinity-based refinement, and both outperformed coastwide IBIs. Regional IBIs reached ≥66% efficacy for three out of four data types (collected nekton, collected benthos, acquired benthos), whereas the best salinity system (Modified Venice System) reached ≥66% efficacy for only two of four data types (collected nekton, collected benthos). Our findings demonstrate the value of regionally refined IBIs as an effective framework for tidal stream management in Texas and along other environmentally variable coastlines. • Salinity-based and regional IBIs outperformed coastwide IBIs. • Regional IBIs were the best-performing classification system. • IBIs performed better with data collected using standardized methods.