CHAPTER 3 



ECOLOGICAL COMMUNITIES 

 AT TIJUANA ESTUARY 



The diversity of habitats at Tijuana 

 Estuary results from the variability in 

 topography, tidal influence, and streamflow 

 inputs. This chapter describes the major 

 communities of organisms at the estuary; 

 additional information on their relationships 

 to other wetlands in southern California is 

 provided in Zedler (1982b). 



3 . 1 PHYSIOGRAPHIC DIVERSITY 



Tijuana Estuary includes eight major 

 natural habitats that we have named: 

 transition from upland to wetland, riparian, 

 salt marsh, salt panne, brackish marsh, 

 estuarine channels and tidal creeks, intertidal 

 flats, and dunes and beach (Table 3.1). Of 

 the wetland habitats, the three that cover the 

 largest area are salt marsh, channels and tidal 

 creeks, and dunes and beach (Table 3.1). 

 Most of the estuarine research has focused on 

 the salt marsh habitat. Regional comparisons 

 of salt marshes appeared in Zedler (1982b). 

 In this chapter, we characterize the dominant 

 species of plants and animals for each habitat 

 and highlight species of special concern. 



Small variations in hydrology and 

 elevation are responsible for the 

 physiographic diversity of Tijuana Estuary 

 (Figure 1.3). Even though the estuary has 

 been substantially altered by catastrophic 

 events and human disturbances, most of the 

 habitats present today probably represent 

 variations on what existed at the turn of the 

 century. One likely exception is the brackish 

 marsh habitat, which appears to be directly 

 dependent on urban runoff. Another is the 

 transition zone, which has borne the brunt of 

 urban and agricultural encroachment. Just 

 how closely it resembles the natural condition 



Table 3.1. Habitat types and areas within the 

 National Estuarine Research Reserve, as 

 determined from the 1986 aerial photo, the 

 1988 vegetation mapping effort, and the 

 geographic information system (Entrix et al. 

 1991). 



will never be known, because there are no 

 remnant areas where undisturbed coastal 

 scrub grades into undisturbed coastal wetland. 



With or without human disturbance, none 

 of the estuarine communities is viewed as 

 static in either species composition or 

 population sizes. Our knowledge of community 

 change is limited by the lack of consistent 

 sampling of most habitats. However, for the 

 most extensive community, the salt marsh, 

 there is now a 10-year record that allows 

 discussion of vegetation dynamics (Chapter 

 5). This data base and the record of variable 

 climatic conditions and streamflow regimes 

 make it clear that Tijuana Estuary is 

 continually subject to environmental 



25 



