PAUL A. MONTAGNA 



Manne Science Institate 

 University of Texas, Austin 



RICHARD D. KALKE 



Marine Science Institute 

 University of Texas, Austin 



CHRISTINE RITTER 



Texas Water Development Board, Austin 



"The bottom of an estuary regulates or modifies 

 most physical, chemical, geological, and 

 biological processes throughout the entire 

 estuarine ecosystem via what could be called a 

 benthic effect." 



*>Y:>3Yetal. (1989) 



CHAPTER FIVE 



Benthic 

 Communities 



INTRODUCTION 



The three major habitats in estuarine marshes are the 

 vegetated tidal marshes, the water column and the 

 sediments. The sediments are both tidal (ranging 

 between the tides) and subtidal (below the tidal 

 elevation range). Benthos (bottom dwelling organisms) 

 live in association with sediments. Benthic 

 invertebrates live either in (infauna) or on (epifauna) 

 the sediments. Estuarine benthic infauna are 

 particularly susceptible to major changes in salinity 

 regimes in the environment because of limited mobility 

 (Kalke and Montagna 1991; Montagna and Kalke 1992; 

 1995; Mannino and Montagna 1997). Freshwater 

 species, which tolerate salinity concentrations, ranging 

 from to 0.5 parts-per-thousand (ppt), are typically 

 found where rivers meet marshes. OUgohahne species 

 live in the upper reaches of estuaries where salinity 

 ranges from 0.5 to 5 ppt. Brackish or estuarine species 

 can accommodate large variations in salinity ranging 

 from 5 to 25 ppt. Marine species generally can not 

 accommodate salinity values lower than 25 to 30 ppt 

 and are limited to the more saline portions of the 

 estuary. Salinity is temporally dynamic at any given 

 location, changing with floods and droughts. Thus, 

 locations of salinity preference zones for various 

 organizations change within an estuary throughout the 

 year. The interaction between dynamic hydrography 

 and salinity preference means the spatial and temporal 

 dynamics of benthic infaunal populations are sensitive 

 indicators of freshwater inflow effects (Montagna and 

 Kalke 1992; 1995). 



Abundance and biomass of infauna may increase if 

 nutrient loading from river input is transformed into 

 food for benthic animals (Montagna and Yoon 1991). 



Chapter Five ♦ 5-1 



