Distribution, abundance, and richness of amphibian and reptile species in the Lower Cypress Tract of Big Thicket National Preserve in relation to salinity and habitat

Waddle, Hardin; Glorioso, Brad

Coastal wetlands are potentially vulnerable to increased salinization due to coastal wetland loss, global sea level rise, and from storm surge associated with tropical storms and hurricanes. The response of coastal ecosystems to increased salinization is difficult to predict, but an understanding of which components of the system are most vulnerable will aid managers in efforts to preserve and mange for resilience in the system. The Lower Cypress tract of Big Thicket National Preserve is a low-lying forested wetland along the Neches River. It is subject to fluctuations in water level from tides and vulnerable to salinity inputs from storm surge. In addition, there arc management concerns related to the dredging of the shipping channel a few kilometers downstream. The Lower Cypress Tract is below the Neches River saltwater barrier, so it is also potentially threatened by management actions that could be taken to maintain freshwater upstream. All of these factors make it important to understand the distribution of animals under current conditions to determine how they might be affected by future management concerns. Anuran amphibians (frogs and toads) are one important part of coastal ecosystems that may be particularly vulnerable to increased salinity. Anurans have water-permeable skin that makes osmotic regulation of body water difficult as ions in water increase. Adult anurans may be able to move out of water that temporarily exceeds their physiological tolerances for salinity, but larvae (tadpoles) are unable to leave the water and will experience increased mortality risk. These effects have consequences to both the distribution and abundance of anurans along the gradient of salinity in coastal environments. Reptiles may also be affected by salinity, but often they have a higher tolerance than amphibians for pulses of salinity that might be expected from storm surges. Most studies of the effect of salinity on anurans have focused at the organismal level to determine how individuals respond to salinity either physiologically or behaviorally, but recently more attention is being paid to the distribution of species in relation to salinity in the environment. The objective of this study is to use site occupancy analysis to model the effect of salinity and habitat on the distribution and abundance of reptile and amphibian species at Lower Cypress Tract. By sampling along a gradient of salinity, and by measuring salinity at each sample of each site, we will be able to use salinity as a covariate for estimates of probability of occurrence of species. This modeling technique will allow us to determine how each species responds to salinity and habitat on the landscape. Ideally this would provide information on how increased salinization in this unit might affect reptiles and amphibians as well as the species that rely on them.