Response of Benthic Organisms to External Conditions in Matagorda Bay

The Lavaca-Colorado Estuary is a major estuarine system along the Texas coast that provides a major economic benefit to the region by supporting a variety of agricultural, residential, industrial, and recreational functions. The Matagorda Bay Health Evaluation (MBHE) component of the LCRA/SAWS Water Project (LSWP) Study Plan was created to assess the environmental effects that could result from further changes to inflow patterns in the Matagorda Bay system. Benthic analysis is one of several measures outlined in the MBHE framework to determine bay health. This study examined how benthic macrofaunal community structure has varied over space and time in response to changes in inflow in both the Lavaca and Matagorda Bay systems. In general, the Matagorda stations E, F and D exhibit healthier ecosystem function than the Lavaca Bay stations. The investigation also found direct relationships between inflow and salinity on benthic communities. While there were few significant relationships found between univariate macrofaunal community measures and salinity or wet/dry periods, there were nevertheless distinct station differences in community structure along salinity gradients. Also, there were three indicator species of freshwater inflow effects. The polychaete Streblospio benedicti declined continuously from freshwater stations to marine stations D. The bivalves Macoma mitchelli and Mulinia lateralis exhibited strong declines along the salinity gradient from freshwater to marine. This implies that reduced flows will cause the upstream communities to take on characteristics of downstream communities. Over the next year, more analyses will be performed to assess if trophic levels are as important as species-level data, and if rare species play a significant role in ecosystem function. Neither of these factors were analyzed in the current preliminary report. Thus, further analysis of existing data, as well as possibly more field studies, is needed to more thoroughly assess the relationship between inflow and community structure in the Lavaca-Colorado estuary