Table 5.8. Relative abundance (%) and total 

 numbers of invertebrates collected at Tijuana 

 Estuary between 1986 and 1989 (from 

 Nordby and Zedler 1991). X = no data. 



nuttallii no longer occurs at Tijuana Estuary 

 and the littleneck clams are half as large. 



Second, the station that is farthest from 

 the river (E-W Channel) sustained the most 

 species and higher densities. The E-W 

 Channel acted as a refuge for Tagelus 

 californianus, Protothaca staminea, and 

 Macoma nasuta. The latter two species had a 

 strong preference for this site. 



Third, the dominant polychaetes were 

 species that are tolerant of wastewater. In 

 Los Angeles Harbor, Crippen and Reisch 

 (1969) found that Capitella spp. and Polydora 



cornuta were most abundant in polluted to 

 very polluted areas. 



Furthermore, a comparative study at Los 

 Pefiasquitos Lagoon, showed that freshwater 

 inflows led to fish kills in 1987 and again in 

 1988. Both floods occurred when that lagoon 

 was closed to tidal flushing; hence the fresh 

 water accumulated and had a major, negative 

 impact on the channel biota (Nordby and 

 Zedler 1991). While the fish kills at Los 

 Pefiasquitos Lagoon were more obvious than 

 the sewage impacts at Tijuana Estuary, the 

 fact that both freshwater disturbances reduced 

 species diversity and abundances lends 

 credence to the argument that freshwater 

 inflows are stressful. 



Recent experimental work with several 

 species of fishes and bivalves (Nordby, 

 Baczkowski, and Zedler, unpubl. data) further 

 demonstrated the effect of salinity dilution. In 

 outdoor mesocosms, bivalve mortality 

 increased with salinity dilution (comparing 

 water of 34, 17, and 8 ppt). Fishes survived 

 reduced salinity more readily than bivalves. 

 Although California halibut had fairly high 

 survival in brackish water, Baczkowski (M.S. 

 thesis, in prep.) found reduced growth rates 

 in diluted sea water, with greater effects 

 among the smallest halibut. 



5.8.5 Summary 



(from Nordby and Zedler 1991) 



In response to sewage inflows, the fish 

 community has become dominated by species 

 that mature rapidly and have an extended 

 spawning season. The bivalve population 

 structure shifted to mostly young individuals. 

 The polychaete fauna became dominated by 

 species that are associated with pollution; 

 they mature early and have prolonged 

 spawning seasons. The cause-effect relation- 

 ship is supported by spatial comparisons 

 within the estuary. The sampling station 

 farthest from the sewage inflows sustained the 

 highest densities of bivalves, while the 

 sampling station in the path of the river 

 supported the fewest species of fish. 



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