Macroinvertebrate Community Dynamics in a Recovering, Hypersaline Estuary Gulf and Caribbean Research

The Bahia Grande is a 6,500-acre tidal basin located at the southernmost tip of Texas. Tidal flow into this coastal estuary was cut off in the 1930s, causing the basin to dry up for ~70 y. A pilot channel connecting the Bahia Grande to tidal waters was constructed in 2005, allowing flooding of the basin to occur. Throughout the period reported herein (2005-2019), the system remained characterized by persistent spatial and temporal episodes of extreme hypersalinity (>70)-a critical factor influencing estuarine community composition and driving key ecological processes. With additional rehabilitation actions forthcoming, characterization of the estuary is essential to evaluate the effectiveness of future restoration efforts. In this study, we analyzed macroinvertebrate data collected from 2005-2019 to evaluate community turnover as well as spatial variation driven by salinity gradients (ranging from 36 to 178). We found 5 distinct ecological groups throughout the study period: 1) early colonizers, 2) high salinity, 3) early stabilization, 4) middle stabilization, and 5) late stabilization. In addition, we found that less saline areas of the basin support different macroinvertebrate assemblages than more saline areas, suggesting that full ecological recovery of the Bahia Grande has yet to be achieved. These findings provide unique insight into the ecological progression of a reflooded, hypersaline estuary (sequence of community turnover, persistence of salinity-driven assemblages, limited recovery of sensitive taxa) while also offering an assessment of the estuary's current rehabilitation status and critical baseline data to inform and evaluate the outcomes of future restoration efforts. Grant no. NA11SEC4810001 Grant no. NA16SEC4810009 Grant no. NA21SEC4810004