Comparison of ecosystem structure and function of created and natural seagrass habitats in Laguna Madre, Texas : final report

There is increasing demand to mitigate the loss of submerged wetland habitats. This project is designed to identify the criteria for a successful mitigation project, and the time for a created seagrass bed to become a functional habitat. Two approaches are taken. The first is a synoptic study of mitigated sites of different ages, the second is monitoring of a recent mitigation site for one year. Ecosystem structure and function is assessed by measuring select variables. Community metabolism and nutrient regeneration are key variables, which indicate the functioning of an ecosystem. Benthic community structure is a key variable that indicates the habitat utilization of an ecosystem. The mitigation sites are compared to three natural reference sites. Aboveground, the mitigation sites resembled natural sites in terms of biogeochemical function, but there were large differences below-ground. The mitigation sites lack sufficient organic material in the sediment for the environment to be fully functional. Benthic community structure at the mitigation sites resembled disturbed environments with high number, diversity, and low evenness. There was also a discernible trend among sites of different ages, that suggest it may take longer than 14-17 years to fully recover. Since this is such a long time, monitoring for one year did not reveal these differences. Future projects to transplant seagrasses for mitigation should consider adding organic matter to the soil to speed the time it takes for the habitat to become fully functional.