Developing a bioassessment framework to inform tidal stream management along a hydrologically variable coast

Water body impairments related to coastal development threaten aquatic life and ecosystem services associated with estuaries. Tidal streams are transitional river-estuary systems that are both ecologically and economically important, but are at high risk for anthropogenic impairment due to their location in areas of rapid coastal development and within the receiving zone of upstream runoff. Although management action is needed to assess how these stressors affect faunal assemblages in tidal streams, natural spatiotemporal variability in tidal and salinity regimes poses a challenge to defining biotic community baseline conditions, and resource managers often lack standardized bioassessment protocols. The goal of this study was to develop multimetric indices of biotic integrity (IBIs) for nekton and benthic macroinfauna in tidal streams along the lower Texas coast, providing a practical bioassessment tool for resource management. Fifteen tidal stream sites were classified into degraded “test” or least-impaired “reference” conditions based on surrounding land use, historical water quality, and watershed population density. Sites were sampled twice per year in the spring and summer of 2020 and 2021 for nekton and benthic macroinfauna, water quality, and physical habitat characteristics. Metrics from historical IBI studies and from directly measured changes in nekton and benthic macroinfauna communities were evaluated. Ten univariate nekton metrics and 6 benthic macroinfauna metrics were selected to create each IBI, encompassing a range of attributes from taxon-level abundances, functional groups, and diversity measures. Although natural spatiotemporal variability and a continuum of degradation among sites made some individual metrics difficult to interpret, the IBIs were generally successful in differentiating test and reference conditions. Recommendations for future refinement of tidal stream IBIs include incorporation of long-term monitoring data, further regionalizing the IBIs based on major climatic regions, sampling multiple sites along the longitudinal salinity gradient, and refining scoring criteria based on stream characteristics. The resulting IBIs represent a significant first step in bioassessment development for Texas tidal streams and provide a useful tool to inform resource management decisions.