FISHERY BULLETIN: VOL. 72. NO. 3 



killed by increased scouring and sediment burial 

 in the absence of the large Macrocystis holdfast. 



The Kellet's v^f\\e\^, Kelletia kelletii, is usually 

 found on rocky substrata or in sand areas adja- 

 cent to more solid substratum. During August 

 1972 we observed a mean density of 0.62/m2 in 

 the combined samples (Table 5). On other occa- 

 sions the density along the transect ranged from 

 0.42 to 0.75/m2. Movement off Del Mar is appar- 

 ently not random, for individual snails were 

 often found in aggregated patterns of distribu- 

 tion. Such aggregations may reflect feeding and 

 reproductive behavior. For example, during the 

 height of the April-May spawning period (Rosen- 

 thal, 1970), mixed aggregations of both male and 

 female Kelletia were repeatedly encountered. A 

 few of these spawning aggregations contained 

 between 200 and 300 individuals; however, the 

 average spawning cluster was about 15 to 20 

 snails. 



Kelletia is basically a carnivorous scavenger; 

 however it does feed on live sedentary poly- 

 chaetes and solitary ascidians. It has been 

 observed eating 22 species of invertebrates and 3 

 species of dead or moribund fish in the subtidal 

 waters off San Diego County (Rosenthal, 1971). 



Predators of Kelletia include the asteroids 

 Pisaster giganteus, P. brevispinus, and Astrometis 

 sertulifera, and the cephalopod Octopz/s bimacula- 

 tus (Rosenthal, 1971). Few other predators are 

 known, although Limbaugh (1955) reported find- 

 ing juvenile Kelletia in the stomachs of pile 

 perch, Rhacochilus vacca. 



Parapholas californica , a bivalve clam, was the 

 most conspicuous terrigenous borer off Del Mar. 

 It primarily bores into sedimentary rocks con- 

 sisting of consolidated mudstones and siltstones. 

 Within the 12 fixed quadrats the Parapholas 

 population density was 0.54/m2. During the moni- 

 toring period there were two recruitments and 

 three mortalities recorded in these quadrats. 

 Pisaster giganteus and P. brevispinus occasionally 

 prey upon Parapholas in this location, as they 

 do in other nearshore areas off San Diego County 

 (Rosenthal, 1971). Predation by sea stars often 

 has the additional effect of breaking the sub- 

 stratum surrounding the clam. 



Paguristes ulreyi is a relatively large, pubescent 

 hermit crab. Almost all were found in discarded 

 Kelletia shells; however, a few crabs were also 

 seen in the shells of Bursa californica. Paguristes 

 was seen throughout the study area, although its 



most frequent habitat appeared to be the silt- 

 stone ledges and consolidated sedimentary 

 mounds located towards the seaward edge of the 

 bed. Each year large aggregations (to 220/m2) 

 of Paguristes were observed in this area from 

 August through October, the crabs often being 

 stacked several layers thick. Paguristes is a 

 scavenger (Pequegnat, 1964), a conclusion sup- 

 ported by our observations of it feeding upon 

 dead invertebrates and pieces of detached algae. 

 Octopus bimaculatus was the only known preda- 

 tor of Paguristes in this location. On two occa- 

 sions, O. bimaculatus was observed moving shells 

 inhabited by Paguristes and one individual was 

 encountered while feeding on a Paguristes. 



Muricea fruticosa is similar in appearance to 

 M. californica, but is usually bushier with a 

 rusty-brown coenenchymal layer and white 

 polyps. Both species of Muricea were observed 

 growing on similar or identical substrata. The 

 mean of 0.27 colonies/m^ in this area (Table 5) 

 is in agreement with the estimate of 0.25 colo- 

 nies/m^ of Grigg (1970). The M. fruticosa popula- 

 tion was almost balanced with respect to mor- 

 tality and recruitment. Fourteen M. fruticosa 

 were recorded in the fixed quadrats during Sep- 

 tember 1968, and 13 individual colonies were 

 found in these same quadrats during December 

 1972, but during this period 17 mortalities and 

 16 recruitments were noted. No predators of 

 M. fruticosa were observed in the study area, 

 and causes of mortality are believed to be similar 

 to those reported for M. californica. 



Tealia coriacea is a solitary, medium sized 

 (4 to 7 cm) sea anemone. It attaches to solid 

 substratum and usually the column is partially 

 buried or enclosed by sediment. Two mortalities 

 and three recruitments were recorded in the fixed 

 quadrats. One Tealia was eaten by a leather 

 star, Dermasterias imbricata, and the other died 

 from an unknown cause. Dermasterias has been 

 reported to eat Tealia spp. and other sea anemones 

 in the Pacific Northwest (Mauzey, Birkeland, 

 and Dayton, 1968), and may on occasion be an 

 important source of mortality in California kelp 

 beds. 



The largest and most conspicuous sea urchin 

 seen off Del Mar was Strongylocentrotus fran- 

 ciscanus. Individual test diameters ranged from 

 5.5 to 18.2 cm. Most of these animals inhabited 

 the sedimentary mounds and boulders located 

 towards the seaward edges of the kelp stand. 



680 



