APPENDIX F 



Effects of Temporality, Disturbance 

 Frequency and Water Flow on an 

 Upper Estuarine Macroinfauna 

 Community 



Christine Ritter Texas Water Development Board, Austin 



Paul A. Montagna University of Texas at Austin, Marine Science Institute (corresponding author) 



Submitted for publication to Marine Ecology Progress Series (draft date: January 14, 2000) 



ABSTRACT: The effects of disturbance frequency and altered flow on estuarine macrobenthic community 

 structure and colonization were studied ia Rincon Bayou, a low-inflow, microtidal, shallow habitat in the upper 

 Nueces Delta, Texas. Three flow treatments were used: increased flow (within a weir), natural flow (control), 

 and decreased flow (between nets). Four disturbance frequency treatments were used: undisturbed, biweekly, 

 monthly, and bimonthly disturbance. Disturbance was imitated by placement and replacement of 6.5-cm 

 diameter trays filled with defaunated sediment. Significant flow velocity differences were found among flow 

 treatments, but turbidity, abimdance, biomass, and diversity were not different. Significant differences among 

 disturbance frequencies were found. Abundance and biomass decreased with increasing disturbance frequency 

 indicating post-disturbance community persistence is important in regulating commimity structure. In the flow 

 experiment, structvire and tray effects were evident because abundance and biomass were higher near structures 

 and in trays than in controls. The higher abundance and biomass in defaunated sediments relative to 

 background sediments indicates disturbance plays an important role in community production of early 

 succession commimities. Collection date was the most important determinant of community structure, thus 

 natural variability overwhelmed effects of both experimental manipulations. The temporal changes were driven 

 by a Streblospio benedicti recruitment event (resulting in densities as high as 1.3 10*^ m^ captured 20 June 1997, 

 and a flood event that began 22 June 1997. After the flood, S. benedicti density declined rapidly and freshwater 

 species invaded, leading to three distinct community states over the 14-week period of the study. The 

 overwhelming significance of "temporality" (i.e., short-term temporal change in commvinity structure) is the 

 unexplained temporal component of community variation in experimental manipulations. Temporality is 

 simply a smaller temporal scale than seasonality. 



KEY WORDS: benthos, disturbance, estuary, flow, macrofauna, Streblospio benedicti 



INTRODUCTION 



Flow dynamics in estuaries result from complex interactions among tidal cycles, estuarine circulation, 

 hydrology, cUmatological forcing, and rate of freshwater inflow. Flow dynamics may vary over the coiu:se of a 

 day, month, season, or on climatological scales. Characteristic flow patterns of an estuary depend on its size, 

 shape, and location. Numerous mechanisms exist by which an estuary's flow regime may affect macrobenthic 

 populations. Changes in flow velocity can affect the sediment flux of ammonium (Asmus et al. 1998), depth of 

 oxygen penetration (Beminger and Huettel 1997), and benthic aerobic respiration and chemical oxygen demand 

 (Boynton et al. 1981). Flow velocit)' also plays an important role in larval dispersal and settlement (Butman 

 1986a, 1986b, 1987, 1989), food availability (Smaal and Haas 1997), and suspension feeder growth rates 

 (Eckman and Duggins 1993, Hentschell 1999a, 1999b). The pattern of flow dynamics (or frequency of change) 



Appendix F ♦ F-1 



