FISHERY BULLETIN: VOL. 78, NO. 2 



then faunal zones should be shifted into deeper 

 waters by an increase in wave activity. The differ- 

 ence in wave energy arriving at the two sides of 

 the canyon allows a partial test of this hypothesis. 

 As predicted, the animal zones described on the 

 southern sandflat were wider and shifted toward 

 deeper water on the northern sandflat (Figures 7, 

 10). Density of crustaceans was highest in 18 m of 

 water, the transition zone was wider, and poly- 

 chaetes did not increase in number until 30 m 

 (Figure 10). Nevertheless, the shape of the curves 

 in Figures 7 and 10, and thus the gross zonal 

 patterns, were remarkably similar. The abundant 

 species were the same on both sides of the canyon, 

 but the rank orders of abundance were not identi- 

 cal (Oliver 1979). Abundance of the numerically 

 dominant crustaceans and the total number of 

 crustaceans was significantly higher along the 

 northern transect (Figures 7, 10). Presumably, 

 this increase was related to the extension of the 

 crustacean zone into deeper water. 



12500 



10000 



CM 



E 

 \ 



00 7500 



_J 

 < 

 Z) 

 Q 



>5000 

 Q 



2500 



NORTHERN TRANSECT 



— Polychaeta 



Crustacea 



Mollusca 







r 



I" 



..J. 



N-2 N-3 fsr-4 N-5 N-6 

 (9 m) (18 m) (24m) (30m) (40m) 

 n=l4 n=24 n=22 n=4 n=8 



STATION 



Figure lO. — Mean number of individuals per square meter and 

 95% confidence limits of major groups along northern transect in 

 Monterey Bay, Calif. N-5 and N-6 were only visited once. 



The predicted effect of increased wave activity 

 on the infaunal zonation was also observed on the 

 zonation of the sand dollar bed. During moderate 

 to heavy sea states, the outer edge of the bed was in 

 6 m on the southern and in 9 m of water on the 

 northern sandflat. In addition, the bed was more 

 than 30 m wider along the northern transect. 

 Therefore, the greater width and seaward depth 

 limits of the sand dollar bed were also associated 

 with stronger wave swell. 



CANYON RIDGE TRANSECT 



Faunal changes along the canyon ridge transect 

 provide further evidence for the relationship be- 

 tween benthic community zonation and substrate 

 motions. The ridge stations (A through D) 

 traversed a substrate movement or disturbance 

 gradient at a constant water depth of 14 m. There- 

 fore, a number of other environmental factors that 

 changed with water depth along the sandflats did 

 not vary along the ridge transect. These included 

 light, temperature, resuspension and settlement 

 of food particles, and the zonation of predatory 

 demersal fish (see Discussion). On the other hand, 

 there was a distinct gradient of substrate move- 

 ment along the sandflats as well as along the can- 

 yon ridge. The type of sediment movement, how- 

 ever, was rather different. The primary substrate 

 movements along the sandflats were caused by 

 wave-generated, oscillating bottom currents, 

 which became greater with decreasing water 

 depth. Water depth was constant along the ridge. 

 This substrate disturbance gradient was caused 

 by a unidirectional (down-canyon) creeping of sed- 

 iment which was greater at stations located 

 nearer to the terrace walls and channels (i.e., sta- 

 tions D and C) (see Environmental Setting). 



Despite these differences, benthic community 

 zonation was similar along the sandflat and can- 

 yon ridge transects. The similarity is partially 

 illustrated by the abundance of polychaetes and 

 crustaceans (Figure 11). The most striking paral- 

 lels, however, were in the distributions of indi- 

 vidual species (Oliver 1979). Species that were 

 highly characteristic of the shallowest sandflat 

 stations (e.g., Scoloplos armiger, Dispio uncinata, 

 Onuphus eremita, Olivella pycna, Euphilomedes 

 longiseta) were found at stations D and C along the 

 ridge (zone of sediment slumping). Species that 

 were most abundant at intermediate sandflat 

 depths were found at intermediate ridge stations, 

 C and B (e.g., juvenile Dendraster excentricus, 



448 



