A PREDATOR-PREY RELATIONSHIP 



BETWEEN THE LEATHER STAR, Dermasterias imbrkata, 



AND THE PURPLE URCHIN, Strongylocentrotus purpuratus 



Richard J. Rosenthal^ and James R. Chess" 



ABSTRACT 



During 1969 and 1970, we spent more than 150 hr underwater observing interaction between the leather 

 star, D. imbricata and the purple sea urchin, S. purpuratus. The majority of the observations were made 

 in shallow (13-15 m) nearshore waters off Pt. Loma, Calif. 



The defensive responses exhibited by the purple sea urchin when contacted by the leather star indicated 

 the presence of a well-developed predator-prey relationship. The responses included retraction of sea 

 urchin podia, depression of spines, gaping and erection of globiferous pedicellariae, and usually move- 

 ment away from the asteroid. 



Within the study area off Pt. Loma, 437 feeding leather stars were encountered underwater, and of 

 these, 204 or 47% were eating S. purpuratus. In contrast, previously published observations by Mauzey, 

 Birkcland, and Dayton (1968) on the feeding behavior of asteroids off the state of Washington indicated 

 that echinoids were excluded from the diet of D. imbricata. We suggest that (1) prey density and avail- 

 ability, (2) search time, (3) taste or gustatory preferences of the sea star, and (4) some form of asso- 

 ciative learning by the leather star may be responsible for the variation in the feeding behavior of D. 

 imbricata in different areas. 



Early laboratory studies by Prouho (1890) and 

 Jennings (1907) described the behavioral re- 

 sponses of sea urchins when encountered by 

 predatory sea stars. More recently, Jensen 

 (1966) recorded the responses of two sea urchin 

 species, Strongylocentrotus drohachiensis and 

 Psammechimis milinris, in the presence of the 

 sea star Marthasterias glacialis. Since field ob- 

 servations on the feeding behavior of sublittoral 

 sea stars were rarely made, the laboratory stud- 

 ies only provided the basis for speculation about 

 natural predator-prey interactions between as- 

 teroids and echinoids. 



Sea urchins might appear to be somewhat im- 

 mune from predatory attacks by other inverte- 

 brate species because they possess such formid- 

 able looking armature. However, Mauzey, Birke- 

 land, and Dayton (1968) observed the sea star 



^ Westinghouse Ocean Research Laboratory, San 

 Diego, CA ; present address, Scripps Institution of 

 Oceanography, University of California, San Diego, 

 La Jolla, CA 92037. 



- Westinghouse Ocean Research Laboratory, San Di- 

 ego, CA; present address. National Marine Fisheries 

 Service, Tiburon Fisheries Laboratory, Tiburon, CA 

 94920. 



Pycnopodia helianthoides feeding on sea urchins 

 both intertidally and subtidally along the shores 

 of Washington state. Leigh ton (1971) reported 

 that two species of sea stars, P. helianthoides 

 and Astwmetis sertulifeiu, feed heavily on ju- 

 venile sea urchins. Also, Rosenthal and Chess 

 (1970) identified the leather star, Deimasterias 

 imbricata (Grube) as a predator of the purple 

 urchin, Strongylocentrotus purpuratus (Stimp- 

 son) off San Diego, California. 



This paper examines in detail the predator- 

 prey interactions observed between the leather 

 star D. imbricata and the purple urchin S. pur- 

 puratus in both laboratory and field situations. 

 Dermasterias imbricata is reported from Prince 

 William Sound, Alaska, to Baja California (Fish- 

 er, 1930; Feder, personal communication) , while 

 S. purpuratus ranges along the Pacific coast of 

 North America from Alaska to Cedros Island, 

 Baja California (Ricketts and Calvin, 1962). 

 Both species occur in intertidal and subtidal sit- 

 uations in cooler temperate climates of the East- 

 ern Pacific; however, south of Santa Barbara, 

 California, the leather star is common only in 

 the sublittoral zone. 



Manuscript accepted October 1971. 

 FISHERY BULLETIN: VOL. 70, NO. 1, 



1972. 



205 



