FISHERY BULLETIN: VOL. 70, NO. 1 



digesting the prey outside of the mouth. Most 

 of the feeding we observed was extraoral in that 

 the leather star's stomach was partially everted 

 out of the mouth (Figure 2) . However, the dis- 

 tinction between the two types of asteroid di- 

 gestion cannot always be determined, since "some 

 species may digest prey partly inside and partly 

 outside the mouth opening at the same time," 

 (Feder and Christensen, 1966, p. 96). In con- 

 trast to our observations off Pt. Loma, Mauzey 

 et al. (1968) found that D. imbricata usually 

 ingested its prey whole. Again, digestion and 

 method of feeding appears to be dependent on 

 the size and form of the prey species. Often 

 leather stars were observed with their stomachs 

 extended into depressions or everted onto the 

 substrata. In this situation we usually could 

 not identify the food item; however, if the 

 leather star's stomach was everted and there was 

 no prey visible, we assumed that it was feeding 

 on detritus. When feeding observations from 

 the various regions are examined in total, the 

 leather star appears to have a highly variable 

 diet; however, when each location is considered 

 separately the diet becomes much more spe- 

 .cialized or restricted. 



PREDATION ON 



Strongylocentrotus purpuratus 



Our data indicate that the leather star is a 

 major predator of S. purpuratus off Pt. Loma. 

 Of the 437 D. imhricata observed feeding, 204 

 or Al^/r were preying on S. purpuratus (Figure 

 1). However, this feeding behavior may be an 

 areal phenomenon or even specific to Pt. Loma, 

 since purple urchin predation by leather stars 

 has not been reported from other regions along 

 the Pacific Coast. Mauzey et al. (1968) did not 

 find urchins included in the diets of D. imhricata 

 off the coast of Washington, despite the presence 

 of S. purpuratus, S. franciscanus, and S. dro- 

 bachiensis. All three of these echinoid species 

 appeared to be available to the D. imbricata that 

 inhabited these subtidal areas (Dayton, personal 

 communication). One explanation for the ex- 

 clusion of urchins in the diets of leather stars 

 off Washington might be the availability of al- 

 ternate or "preferred" prey species. The seden- 



H" ^ii?""^^ 





Figure 2. — Dermasterias imbricata feeding on a purple 

 urchin 15 m underwater off Pt. Loma. Note the S. pur- 

 puratus pedicellariae attached to the leather star's 

 epidermis. 



tary or sessile invertebrates which Mauzey et al. 

 (1968) found in the diets of D. imbricata off 

 Washington did not appear to be important nu- 

 merical constituents of the epibenthic community 

 off the Pt. Loma study site. However, the sea 

 urchin population had increased to a point where 

 Leighton, Jones, and North (1966) suggested 

 that perhaps an ecological imbalance had devel- 

 oped within these stands of giant kelp. Further, 

 North and Pearse (1970) reported that an ap- 

 parent population "explosion" of herbivorous sea 

 urchins had occurred along the coast of Southern 

 California. 



In addition to the high percentage of leather 

 stars observed eating purple urchins, we found 

 that 51% of all D. imbricata examined off Pt. 

 Loma had S. purpuratus globiferous pedicel- 

 lariae attached to their epidermis (Figures 2 

 and 3). A laboratory experiment was per- 

 formed to determine the maximum length of 

 time that globiferous pedicellariae remain at- 

 tached to the leather star following contact with 

 a purple urchin. We found that following at- 

 tachment, 3 to 4 days elapsed before the pedi- 

 cellariae detached from the leather stars. A 

 D. imbricata with purple urchin pedicellariae 

 attached to it provided us with indirect evidence 

 that the leather star had either eaten, or had con- 

 tact with, one or more purple urchins within the 

 last 3 to 4 days. In either case, the number of 



208 



