FISHERY BULLETIN: VOL. 69, NO. 3 



partially underneath or even crawling over the 

 sea star attempting- to get to the food item, and 

 at times a feeding sea star would also be grasping 

 from one to four K. kelletii. A few of these 

 interspecific feedings were quite distinct in ap- 

 pearance, especially when both species were 

 scavenging larger prey such as dead fishes. 

 Three P. gigante.us and 28 K. kelletii were ob- 

 served feeding simultaneously on a dead barra- 

 cuda, Sphyraena argoitea, off Quast Rock on 

 December 31, 1968. However, most of the feed- 

 ing convergences observed were not as obvious 

 as this; usually they involved only a single sea 

 star and two or three whelks. Convergent 

 feeding behavior has been noted 65 times in 

 these four locations over a 2-year period. On 

 one occasion, five separate convergent groups 

 were observed within a 400 m- area off" Point 

 Loma. 



Direct competition for food was most evident 

 when both species were scavenging carrion or 

 moribund organisms. However, in situations 

 where P. gigantens had captured or killed live 

 prey, K. kelletii was rarely observed with its 

 proboscis extended into the prey. It is probable 

 that feeding by the whelk usually takes place 

 on a secondary basis after the sea star has de- 

 parted. The percentage of prey that is left un- 

 eaten by P. giganteus following a feeding is 

 unknown. 



These convergent feeding groups were not 

 limited to K. kelletii and P. giganteiis. K. kelletii 

 has been observed feeding interspecifically with 

 two other sea stars, Dennasterias imbricata and 

 Pisastei- brevispimis. Other scavenging or car- 

 nivorous types of epibenthic invertebrates which 

 have been found in these sea star-whelk feeding 

 groups include the gastropod Mitra idae and the 

 hermit crab Pagvristes ulreyi. 



PREDATION ON Kelletia kelletii 



There have been few natural predators of 

 K. kelletii rejiorted in the literature. The moon 

 snail, Polinices leivisii, was observed by Mac- 

 Ginitie and MacGinitie (1949) to have drilled 

 and eaten a live K. kelletii in a laboratory tank. 

 Juvenile K. kelletii were found in the stomachs 



of young pile perch, Rhacochilus vacca, by Lim- 

 baugh (1955) . Three predators of K. kelletii ob- 

 served during diurnal hours in these subtidal lo- 

 cations were Pisaster brevispinus, P. giganteics, 

 and the cephalopod Octopus bimaculatus. How- 

 ever, only predation by P. giganteus is considered 

 at this time. 



P. giganteus is a major predator of K. kelletii 

 on the nearshore reefs that I studied. During 

 the 214-year study i^eriod, 42 separate feedings 

 were observed in which, the sea star was in the 

 act of digesting a whelk; and 53 other times, 

 P. giganteus were found attacking K. kelletii. 

 Five separate attacks by P. giganteiis on K. 

 kelletii were observed in a single dive off middle 

 Coronado Island, Baja California (lat 32°25' N, 

 long 117°16' W) on December 3, 1969. 



The sea star usually fed by attaching tube feet 

 to the substratum and the shell and the oper- 

 culum of the K. kelletii. P. gigaiiteus was usually 

 observed in a humped or arched position while 

 attacking and feeding on the whelk. In this 

 feeding position, a sea star can bring into play 

 a greater number of tube feet and exert max- 

 imum pull on the operculum and shell of the 

 whelk while still remaining attached to the sub- 

 stratum (Feder and Christensen, 1966). K. kel- 

 letii were not swallowed or ingested whole by 

 P. giganteus; instead, digestion appeared to take 

 place extraorally as is the case with other food 

 items. The whelk's operculum was either torn 

 away or pulled out of the shell opening by the 

 tube feet, and the sea star's stomach was inserted 

 into the shell. Bullock (1953) suggested that 

 predation on the intertidal snail Acanthina spi- 

 rata by carnivorous asteroids was slight, and that 

 possibly po.ssession of a heavy operculum ac- 

 counted for the nonresponsive behavior the snail 

 displayed in the presence of predatory sea stars. 

 The operculum of K. kelletii does not eliminate 

 sea star predation; however, the structure ap- 

 parently does increase the time necessary for an 

 asteroid to complete the feeding process. 



The A', kelletii which were attacked by P. 

 giganteus ranged between 18 and 120 mm in 

 shell length (siphonal canal to the apex) ; how- 

 ever, approximately lO'i of these feedings in- 

 volved K. kelletii greater than 60 mm in length. 

 This size class, greater than 60 mm, was com- 



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