ROSENTHAL and CHESS: PREDATOR-PREY RELATIONSHIP 



table contained circulating seawater approxi- 

 mately 0.3 m in depth. Bricks were scattered 

 around the bottom of the tank to provide the 

 urchins additional substratum and cover. The 

 concentration of leather stars to purple urchins 

 was considerably higher than normally found in 

 the field; however, we felt that the increased 

 number of leather stars might increase our 

 chances to observe predation in the laboratory. 



FEEDING BEHAVIOR OF 



Dermasterias imbricata 



The widespread distribution of D. imbricata 

 along the Pacific coast of North America is par- 

 tially reflected in its feeding behavior. Dermas- 

 terias imbricata is an active predator that feeds 

 primarily on benthic invertebrates, although it 

 has been observed feeding on algal and detrital 

 material. In areas containing abundant prey, 

 both motile and sessile in habit, the leather star 

 seems to exhibit a "preference" for the sessile 

 forms, in that sessile species are eaten more often 

 than the motile forms. Asteroid feeding be- 

 havior experiments by Landenberger (1968) and 

 Mauzey et al. (1968), showed that the sea star 

 Pisaster ochraceus exhibited preferences for 

 sedentary mussels to alternative food items of- 

 fered them. Paine (1969) suggested that few 

 additional prey species are consumed as long as 

 mussels are available to P. ochraceus. Landen- 

 berger (1968) also found that Pisaster gigaydeus 

 preferred mussels to four gastropod species 

 which were offered to the asteroids as alterna- 

 tive prey. Additional observations by Rosenthal 

 (1971) indicated that, in nature, P. giganteits 

 displayed a preference for prey which was either 

 immobilized or sedentary in habit. 



Feder (1959) felt that differences in the diet 

 of P. ochraceus were largely dependent on chang- 

 es in prey availability within each intertidal lo- 

 cation. A similar situation appears to exist with 

 D. imbricata, at least in those regions where 

 feeding observations have been made. Mauzey 

 et al. (1968) found D. imbricata to be a major 

 predator of actinians along the rocky outer coast 

 of Washington; yet, in the protected San Juan 

 Islands, its diet was composed primarily of holo- 

 thurians. At Waddah and Tatoosh Islands off 



Washington, they observed D. imbricata feeding 

 on encrusting sponges, colonial tunicates, hy- 

 droids, and calcareous ectoprocts. Other local- 

 ities indicate still additional diets. Feder (per- 

 sonal communication) observed leather stars 

 with stomachs everted on eel grass, Zostera ma- 

 rina, in the intertidal regions of Prince William 

 Sound, Alaska. 



Off Pt. Loma, California we have observed 

 D. imbricata feeding on Strongylocentrotus pur- 

 puratus (sea urchin), Strongylocentrotus frayh- 

 ciscanus (sea urchin), Astrometis sertulifera 

 (sea star) , Pisaster giganteus (sea star) , Tethya 

 aurmitia (sponge), Leucilla nuttingi (sponge), 

 Membranipora membranacea (bryozoan), Epi- 

 actis prolifera (sea anemone), Corynactis cali- 

 fornica (sea anemone), Astrangia lajollaensis 

 (coral), Muricea californica (gorgonian), Kel- 

 letia kelletii (gastropod) egg capsules, unidenti- 

 fied sponges, holothurians, and detritus. Stron- 

 gylocentroti's pxirpuratus made up 47% of the 

 feeding observations; L. nuttingi, 13%; A. ser- 

 tulifera, A'}f ; detritus, 27% ; and all other items 

 combined, 9''r, out of a total of 437 feeding 

 leather stars (Figure 1). Over a one-year per- 

 iod, 927 D. imbricata were examined for food 

 items; however, some of these observations were 

 repetitive in that the same leather star was re- 

 examined on a different day of observation. 



Feeding was accomplished by either ingesting 

 the prey whole or by everting the stomach and 







50 100 150 200 



NUMBER of OBSERVED FEEDINGS 



250 



Figure 1. — Leather star feeding observations (N = 437) 

 ofiF Pt. Loma, California from November, 1969 through 

 November, 1970. 



207 



