. Bulletin. Science; Natural history; Natural history. 134 SOUTHERN CALIFORXL-\ ACADEMY OF SCIENCES Creoidulo a 300 ZOO- IDG. LM a COTCpy ? Middle S Bottom _^ .i i^Jj J .J^ k 200- 100 r-l-u. ^J%h rfl r+^ ^ -f^ -J^ -J^ 200 100 .. J J J ,. J .^ ^iL 100- B-CoifofPico -r^ -r-m tfe_ 200 100 f*>T» E^ A. JJASONDJFMAMJJASOND 1975 1976 Fig. 2. Monthly abundances (x = 95°o ) of moUusks (all species) in each vertical zone. Each value represents the mean of 3 fJuly-September 19''5) or 5 (October 1975-December 1976) repHcate samples. Habitat Reef. The most important factor may be water m
. Bulletin. Science; Natural history; Natural history. 134 SOUTHERN CALIFORXL-\ ACADEMY OF SCIENCES Creoidulo a 300 ZOO- IDG. LM a COTCpy ? Middle S Bottom _^ .i i^Jj J .J^ k 200- 100 r-l-u. ^J%h rfl r+^ ^ -f^ -J^ -J^ 200 100 .. J J J ,. J .^ ^iL 100- B-CoifofPico -r^ -r-m tfe_ 200 100 f*>T» E^ A. JJASONDJFMAMJJASOND 1975 1976 Fig. 2. Monthly abundances (x = 95°o ) of moUusks (all species) in each vertical zone. Each value represents the mean of 3 fJuly-September 19''5) or 5 (October 1975-December 1976) repHcate samples. Habitat Reef. The most important factor may be water motion generated by storms and or tidal currents, which undoubted!}" dislodges many mollusks from the kelp fronds. As the degree of motion and removal probably is greatest in the canopy and as all dislodged mollusks must crawl back onto the kelp via the bottom zone, the obserA"ed patterns of vertical zonation could be explained most often by differential water motion dislodgement with subsequent concentration in the low- er zones. Other factors may be important, however, especially during extended periods of relatively calm conditions. For example, mollusks may avoid the canopy during calm summer months at Habitat Reef because of warmer surface temperatures and or greater light intensity. Additionally, predators may influence the vertical distribution of mollusks at Habitat Reef, although their effect is difficult to assess. Dense alga cover has been demonstrated to decrease the effectiveness of sea star predation fWatanabe 1984) as well as predation by fishes (Vince et al. 1976: Heck and Thoman 1981: Peterson 1982; Stoner 1982). Consequently, one could predict that most mollusks would be present in the bottom and canopy regions at Habitat Reef because kelp biomass consists of a dense and "bushy"" cluster of sporoph\ies in the bottom, a dense mass of interdigitating fronds and blades in the canopy, and a relatively sparse mass of fronds and blades in t
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