chaiactensdc of an estuary may play an important role in determining macrobenthic community structure 

 (Pearson and Rosenberg 1987). At^'pical changes in flow dynamics, such as those occurring during storms, may 

 also be important determinants of benthic commumt}' structure (Renaud et al. 1996). 



Physical disturbances (e.g., dredging, trawling, or major storms) affect macrobenthic communities within the 

 context of the flow regime and ambient environmental conditions. ITie frequency of disturbance may be a 

 major determinant of community structure. Connell (1 978) h)'pothesi2ed that more frequent disturbances will 

 maintain a commumty at an earlier stage of succession, which is characterized by lower diversit)', abundance, 

 and biomass than reference communities of lower disturbance frequencies. Because flow dynamics can vary on 

 short temporal scales, it could be an important physical regulator of community change. 



The purpose of this study was to determine temporal effects of disturbance frequency and altered water flow 

 on macroinfauna early succession. Macrobenthic recruitment and community structure were expected to 

 change for each flow treatment (Rhoads and Young 1970). Increased flow was expected to promote 

 suspension feeder populations and growth rates (Hentschel 1999a; 1999b). Communities subjected to greater 

 frequencies of disturbance were expected to have lower diversity, abundance and biomass than those subjected 

 to less frequent disturbance as predicted by Connell (1978). Early succession was expected to be dynamic and 

 vary among flow treatments because the dominant organism at the study site, Streblosio benedicti . is an 

 opportunistic species (Grassle and Grassle 1974), can recruit in excess of 25,000 m ' a month (Levin 1984), and 

 can increase growth rates with flow speeds between 9 and 18 cm s' (Hentschel 1999b). 



METHODS 



Site Description 



Rincon Bayou is a tidal creek in the Nueces-Corpus Chnsti Bay estuarme ecosystem. Rincon Bayou lies west of 

 Nueces Bay and north of the Nueces River. It may have once been the primary channel of the Nueces River 

 but is now connected to the Nueces River via an overflow channel constructed in October 1 995 (Irlbeck and 

 Ergerl998). 



Rincon Bayou is a low-inflow environment, subject to hypersalinity during droughts and freshets during floods. 

 Monthly discharges from the Nueces River into Rincon Bayou ranged from -1200 to 300,000 m' between May 

 and December, 1996, but about 60 % of daily discharges were < ± 1200 m' (USGS unpublished data 1997). 

 Rincon Bayou receives little tidal influence (< 0.2 m) and water movement is predominandy wind driven (Salas 

 1994), or inflow driven during floods. 



The location within Rincon Bayou, station C (27° 53.927' N, 97° 36.250' W), was chosen because it lies 

 approximately along the axis of prevailing winds, which blow from the southeast and south (Port of Corpus 

 Christi Authority 1993). In addition, station C is part of a quarterly sampling program begun in 1994 from 

 which a historical context can be drawn. Surface sediment is approximately 86 % silt and clay, and contains 0.7 

 % total organic carbon. Sahnity averages 40 %o, but has ranged between 0.2 - 160 %o over a four-year 

 monitoring period (Montagna unpublished data). Dissolved oxygen averaged 7.36 mg 1 ', but has ranged 

 between 1.01 - 15.32 mg 1 ' over the same period. Six macrobenthic taxa were commonly found at station C: 

 the polychaetes Streblospio benedicti Webster and Laeoneris culven (Webster), the crustaceans Ostrocoda and 

 Hemicyclops sp., and insect larvae of Ceratopogonidae and Chironomidae. 



Experimental Design 



The goal of the present study was to determine the effects of flow alteration and disturbance frequency on 

 short-term changes of macrofauna (Fig. 1). Three flow treatment levels were used: increased flow, decreased 

 flow, and control. Increased flow was effected through the use of weirs parallel to currents. Weirs are used to 

 increase water pressure, and hence flow, over a specific area (Fig. 2a). Decreased flow was effected through the 

 use of nets perpendicular to currents. Nets are commonly used to reduce wave energ)' by slowing water 

 velocity. Control flow was areas perpendicular, but away from structures and represents the natural flow 

 conditions of the Bayou (Fig. 2b). 



F-2 V Effects ofTemporality, Disturbance Frequency and Water Flow 

 on an Upper Estuarine Macroinfauna Community 



