Long-term Trends in Lavaca-Colorado and Guadalupe Estuaries

Principal Investigator

A 20-year study from 1988 to 2008 in the Lavaca-Matagorda Estuary (i.e., Lavaca and Matagorda Bays) demonstrated that benthic abundance, biomass, and diversity were declining at log-scale rates.1 This raises serious environmental questions concerning the middle Texas coast: 1) Will the trend continue? 2) What are the ecosystem consequences, and will fish run out of forage food? 3) Why is this happening at all? 4) Is this a natural trend occurring elsewhere in Texas?

The potential disappearance of benthos is of great concern. They are excellent bioindicators of sediment quality and estuarine health because they are relatively long-lived, fixed in place, integrate variations in the overlying water column over time, and are forage for commercial and recreational fish species.

The initial report1 suggested that the benthic decline could be due to alterations in freshwater inflow patterns due to climate change. Freshwater inflow drives water quality in Texas bays as indicated by changes in nutrient and chlorophyll concentrations.2 Past studies in Lavaca and Matagorda Bays have demonstrated that long-term hydrological cycles (which are driven by long-term climate cycles and other changes) affect freshwater inflow and water quality, and in turn regulate sediment quality as indicated by benthic productivity and diversity.3 However, there are many emerging environmental stressors developing over time such as increased temperatures and more frequent occurrence of low dissolved oxygen,4 and increased water diversion and pollution. Individually, these stressors alone would not cause harm, but when acting in concert with one another, could prove harmful.

Long-term research is important because most ecological questions cannot be answered with short-term studies alone. This is particularly true for questions about sublethal effects and consequences of multiple stressors; or the effects of freshwater inflow because of large year-to-year variability in climate and weather, which leads to periods of floods and droughts. Biodiversity and community structure are powerful assessment metrics because sensitive species are reduced or die, while tolerant species survive or thrive during prolonged unfavorable conditions. Hence, analysis of biological diversity data has been used to assess ecosystem health everywhere on Earth.

Led by Dr. Paul Montagna, HRI Chair for HydroEcology, the goal of this project is to complete a 31-year time series in two ecosystems — the Lavaca-Colorado Estuary and Guadalupe Estuary (i.e., San Antonio Bay) — to determine if benthic decline is still occurring, if it is regional in scale, and what might be causing it (if it is still occurring).


Project Objectives:

  1. Determine if the benthic decline between 1988-2008 in the Lavaca-Colorado Estuary continued from 2009-2019 by completing analyses of archived benthic samples.
  2. Determine the ecosystem consequences of declining benthos on epibenthic and nektonic populations by comparing benthic data with existing Coastal Fisheries Monitoring data.
  3. Determine the cause of the decline by comparing results in the Lavaca-Colorado Estuary with results from the Guadalupe Estuary and by examining existing water and sediment quality data.


This project runs March 2021 through December 2022.



1 Pollack, J.B., T.A. Palmer, and P.A. Montagna. 2011. Long-term trends in the response of benthic macrofauna to climate variability in the Lavaca-Colorado Estuary, Texas. Marine Ecology Progress Series 436: 67–80.

2 Montagna, P.A., X. Hu, T. A. Palmer, and M. Wetz. 2018. Effect of hydrological variability on the biogeochemistry of estuaries across a regional climatic gradient. Limnology and Oceanography 63:2465-2478.

3 Kim, H.-C. and P.A. Montagna. 2012. Effects of climate-driven freshwater inflow variability on macrobenthic secondary production in Texas lagoonal estuaries: A modeling study. Ecological Modelling 235-236: 67-80.

Montagna, P.A. and R.D. Kalke. 1995. Ecology of infaunal Mollusca in south Texas estuaries. American Malacological Bulletin 11:163-175.

Palmer, T.A., P.A. Montagna, J.B. Pollack, R.D. Kalke and H.R. DeYoe. 2011. The role of freshwater inflow in lagoons, rivers, and bays. Hydrobiologia 667: 49-67.

4 Montagna, P.A., J. Brenner, J. Gibeaut, and S. Morehead. 2011. Coastal Impacts. In: Schmandt, J., G.R. North, and J. Clarkson (eds.), The Impact of Global Warming on Texas, 2nd edition. University of Texas Press, Austin, Texas, pp. 96-123.