Table 3.6. Average density (number/m 2 ) and percent of total individuals (relative 

 abundance) for each of the most numerous species of sandy bottom communities at Mugu 

 Lagoon and Tijuana Estuary (modified from Peterson 1977). 



Species 



Cryptomya californica 

 Callianassa californiensis 

 Protothaca staminea 

 Sanguinolaria nuttalli 

 Dendraster excentricus 

 Tagelus californianus 



In 1980, Hosmer resampled several areas 

 that were included in his 1977 thesis work, 

 and Rehse (1981) compared the two data sets 

 on bivalves and callianassid shrimp. Flooding 

 caused mass mortalities of many species. 

 Absent from the 1980 collections were the 

 yellow clam (Florimentis obesa), egg cockle 

 (Laevicardium substriatum), bentnose clam, 

 white sand clam (Macoma secta), California 

 mactra (Mactra californica), Washington 

 clam (Saxidomus nuttalli), Carpenter's tellen 

 (Tellina carpenteri), and Callianassa gigas. 

 The dominant bivalve before the 1978-80 

 period was the purple clam, while the 

 dominant in 1980 was false mya. 



Juvenile recruitment was high after the 

 1980 floods, particularly for ghost shrimp, 

 whose density increased 72% while biomass 

 decreased 95%. Significant decreases in mean 

 size were also recorded for ghost shrimp, blue 

 mud crab, and purple clam, indicating that 

 mass mortality was followed by recruitment. 

 However, the mean sizes of two species (false 

 mya and littleneck clam) were not 

 significantly less than in 1977, which 

 suggested that both survived the stresses of 

 reduced salinity and altered substrate. 



These changes support the hypothesis that 

 benthic macrofauna are strongly associated 

 with sediment particle size. Dune washover 

 events and dredging activities also alter 



substrate type and add to our understanding of 

 substrate dependency. The dredging of Oneonta 

 Slough in 1987 removed some of the sand that 

 was deposited in 1983 but left behind a coarse 

 substrate. Sea storms in December 1986 and 

 December 1987 again added sand to the 

 channel along Seacoast Drive. Despite these 

 disturbances, bivalves continued to persist, 

 although in lower numbers than where 

 wastewater influence was not as severe 

 (Nordby and Zedler 1991). Lowered salinity 

 also contributes to compositional change, as 

 has been shown for both wastewater inflows 

 (cf. Chapter 5 and Nordby and Zedler 1991), 

 and river flooding (Zedler et al. 1984b, 

 Peterson 1975; Onuf 1987). 



During 1983, El Nifto conditions increased 

 sea levels an average of 15 cm (R. Flick, 

 Scripps Institution of Oceanography, pers. 

 comm.), which ameliorated the impact of 

 freshwater flooding. Unusual species were 

 noted in the estuary following the 1982-83 

 El Nifto. Swimming crabs (Portunis sp.) 

 were so abundant in 1984 that some people 

 collected them by the bucket for food 

 (Jorgensen, pers. comm.). Casual sampling of 

 the benthos during closure produced mainly 

 polychaete worms (Spionidae, Figure 3.21), 

 amphipods (Corophidae), and water boatmen 

 (Trichocorixia; K. Dyke, SDSL), pers. comm.). 

 The polychaetes and amphipods dominated 

 these collections, constituting 97% of the 



51 



