passive organisms deposition (Butman 1986a; 1989), or spionid organismal growth (Hentschel 1999a; 1999b). 

 The third community state is related to the flood event that began 22 June 1 997. SaUnit)' dropped to %o by 02 

 July and had increased to only 2 %o by 01 August. The persistence of low salinity over a period of more than 

 one month probably led to declines in total abundance and biomass following the flood (Figs. 7 and 8). For 

 example, when salinity was reduced from 19.9 %o to 3.19 %o, S. benedict stzrvived up to 1 1.5 h, whereas P. 

 comuta expired within 7 hours, and Leptocheirus plumulosus remained active and normal (Sanders et al. 1965). 

 Differential salinity tolerance explains persistence and species changes, and is one component of temporality. 



The strong response of macroinfauna to temporally variable, ambient, environmental conditions rather than to 

 experimental manipulations indicates experimental effects were less important than temporal community 

 response to natural environmental fluctuations. This is almost certainly true for flow treatment manipulations 

 for which no significant effects on macrobenthos were found. Flow effects probably exist, but are barely 

 detectable due to environmental variation. Though significant distvirbance frequency effects were found, 

 community structure differences were masked by community composition similarities in all treatments within 

 collection dates. 



Temporality is the controlling feature of the Rincon Bayou benthic community, explaining most of the variance 

 in abundance and biomass (Table 2). Rincon Bayou is an extreme environment, ranging from hypersalinity in 

 droughts and freshwater in floods. From 1994 - 1997, salinity at station C ranged between and 160 %o. The 

 present study unintentionaDy captured a flood event that led to a sudden drop of salinity from 18 to %o, 

 which persisted for more than a month (Fig. 4). Such a salinity change exceeds the tolerances of most 

 euryhaline species (Sanders et al. 1965), and led to an increased populations of chironomid larvae and decreased 

 populations of Streblospio benedicti and Laeoneris culveri (Fig. 9). In Rincon Bayou, community change 

 occurring in response to physical disturbance appears to be limited by natural environmental variation through 

 time, which we call temporality. Temporality is simply the short-term analogy to longer-term seasonality. 



Summary 



Succession is controlled more by the natural tempo of environmental variation (e.g., availability of recruits, and 

 coincidence of rainfall) than by small-scale events (e.g., patch defaunation and water flow). How appears to be 

 a less important determinant of community structure for Rincon Bayou station C compared to natural variation 

 of background environmental characteristics (e.g., salinity), but appears to influence abundance, biomass, and 

 diversity. Rincon Bayou is generally a low-inflow, microtidal, shallow water habitat subject to broad salimty 

 fluctuations concomitant with periodic drought and flood events. During the period of the present study, 

 sample collection date was the most important factor in determining community structure indicating 

 experimental effects were overwhelmed by natural environmental variation arising from recruitment and flood 

 events. Within the context of natural temporal variation, significant differences were found among disturbance 

 frequency treatments. Community abundance, biomass, diversity, and evenness decreased with increasing 

 disturbance frequency indicating the importance of post-disturbance community persistence in determining 

 community structure and succession state, and possible tray effects. Disturbance in the form of flow alteration 

 or defaunated sediment increased community abundance and biomass, indicating disturbance may increase 

 production of early succession macrobenthic communities in estuaries. 



Acknowledgments 



Funding for research in Rincon Bayou was provided in part by the U.S. Bureau of Reclamation (Grant No. 4- 

 FG-60-G4370) and die Texas Water Development Board (Research and Plaiming Fund Contract No. 94-483- 

 046) to the University of Texas at Austin, Marine Sciences Institute. Partial support, via the Lund Fellowship, 

 was granted by the University of Texas Marine Science Institute. The authors also acknowledge Rick Kalke and 

 Robert Biurgess for assistance in the field, and Carol Simanek for data management. 



LITERATURE CITED 



Asmus RM, Jensen MH, Jensen KM, Kristensen E, Asmus H, Wille A (1998) The role of water movement and 

 spatial scaling for measurement of dissolved inorganic nitrogen fluxes in intertidal sediment. Estuar Coast 

 Shelf Sci 46:221-232 



Appendix F ♦ F-9 



