FOOD AND HABITAT OF THREE SWITCH-FEEDING FISHES IN 

 THE KELP FORESTS OFF SANTA BARBARA, CALIFORNIA 



Milton S. Love and Alfred W. Ebelinqi 



ABSTRACT 



Diets and habitat distributions were compared among the blue rockfish, Sebastes mystinus, kelp bass, 

 Paralabrax clathratus, and olive rockfish, Sebastes serranoides , all of which cooccur in areas of reef and 

 giant kelp off Santa Barbara, Calif The three species make up a feeding guild of large-mouthed 

 predatory fishes that commonly switch among planktonic prey, nektonic prey (fish and squid), and 

 substrate-oriented prey (invertebrates that live on or about reef and plant surfaces). At the semi- 

 isolated study site, blue rockfish, which are somewhat better adapted than the others to ingest and 

 retain small particles, ate relatively more plankton than did individuals of the other species, while 

 olive rockfish ate more fish. Kelp bass had both the broadest diet and habitat distribution. All three 

 species ate more plankton during winter-spring, yet had smaller dietary overlaps then. Olive rockfish 

 ate more fish and less plankton at the heavily foliaged study site than they did over a deeper kelpless 

 reef farther offshore. The three species tend toward deeper and calmer areas of the reef; kelp bass and 

 olive rockfish prefer clear-water areas of dense kelp; kelp bass often concentrate near the outer 

 kelp-bed margin; and both rockfishes prefer areas of high-relief rocky bottom. The morphologically 

 similar kelp bass and olive rockfish may segregate spatially, perhaps reducing mutual interference. As 

 inferred from other studies and our own, areal variation in feeding habits of the three species may 

 reflect their environmental tolerances, range limits, numbers of competitors, food supplies, habitat 

 structures, or predator densities. The closely related rockfishes show least dietary overlap between 

 themselves and most overlap with the more distantly related kelp bass. 



Kelp-bed fishes that have similar diets and habi- 

 tat requirements form feeding guilds. For exam- 

 ple, Bray and Ebeling (1975) described how three 

 species of small picker-type microcarnivorous 

 fishes share substrate-oriented prey and plankton 

 in the kelp forests off Santa Barbara, Calif. Also 

 occupying the midwater zone between kelp canopy 

 and reef bottom is a feeding guild of larger, pre- 

 datory fishes. These include two members of the 

 scorpaeniform family Scorpaenidae, the blue 

 rockfish, Sebastes mystinus, and olive rockfish, iS. 

 serranoides, and one member of the perciform fam- 

 ily Serranidae, the kelp bass, Paralabrax clath- 

 ratus. All have fusiform bodies, head spines re- 

 duced or absent, large flexible fins, large mouths, 

 and numerous well-developed and closely set gill 

 rakers. Blue rockfish are ovate with blue-gray 

 bodies stippled darkly above the flanks; olive 

 rockfish and kelp bass are more elongate with 

 brownish bodies and characteristic arrays of white 

 blotches along their backs. The three species are 

 similar enough in general appearance to be 



'Marine Science Institute and Department of Biological Sci- 

 ences, University of California, Santa Barbara, CA 93106. 



Manuscript accepted June 1977. 



FISHERY BULLETIN: VOL. 76, NO. 1, 1978. 



grouped by most Santa Barbara fishermen simply 

 as bass: blue, Johnny, and calico basses, respec- 

 tively. They form the nucleus of a shallow- water 

 sport fishery at the edges of the Santa Barbara 

 kelp forests. 



Our primary interest was how the three species 

 share food and space over a single, semi-isolated 

 area of reef and kelp (Naples Reef) near Santa 

 Barbara. We emphasized the most common size 

 range of fishes sighted, large juveniles to small 

 adults. Previous studies indicated that the species 

 are generalized carnivores, occurring throughout 

 the water column and eating a wide variety of 

 large and small prey of all major categories (Lim- 

 baugh 1955; Young 1963; Gotshall et al. 1965; 

 Quast 1968a-d; Turner et al. 1969). We wanted to 

 see if the three species can switch (change almost 

 entirely) from eating one prey type to another, and 

 under what circumstances they may do so. Using 

 data from other studies, we also investigated food 

 habits of olive rockfish from a deeper, offshore 

 population living in an environment quite unlike 

 that of the kelp bed, and we investigated the spa- 

 tial distributions of all three species at Naples 

 Reef and in an adjacent island environment. 



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