ABUNDANCE AND VERTICAL DISTRIBUTION OF FISHES IN 



A COBBLE-BOTTOM KELP FOREST OFF 



SAN ONOFRE, CALIFORNIA 



Ralph J. Larson 1 and Edward E. DeMartini 2 



ABSTRACT 



Using visual belt transects on the bottom and vertically stratified belt transects taken with movie cameras in 

 the water column, we assessed the species composition, vertical distribution, and standing stock of fishes in a 

 forest of giant kelp and a nearby kelp-depauperate area off San Onofre, California. The volume of water- 

 column "cinetransects" was calibrated for water clarity. Species such as garibaldi, blacksmith, and various 

 rockfishes, which depend on high-relief rocky substrates, were rare or absent in these low-relief, cobble- 

 bottom habitats. The species present in the kelp forest apparently did not depend on high-relief rock, at least 

 in the presence of kelp. These species fell into three groups, based upon their vertical distributions: "canopy" 

 species (kelp perch, giant kelpfish, and halfmoon), which occurred mainly in the upper water column; "cos- 

 mopolites" (kelp bass, white seaperch, and senorita) .which occurred throughout the water column; and "bot- 

 tom" species (California sheephead and various seaperches), which occurred mainly near the bottom. 

 Despite the absence of reef-dependent species, estimated standing stocks of 388-653 kg/ha in the San 

 Onofre kelp forest were as large or larger than estimates made by others in kelp forests located on higher 

 relief bottoms. The kelp-forest areas at San Onofre also supported a larger standing stock of fishes (other 

 than barred sand bass) than the adjacent area with little kelp. The relatively large standing stock of fishes in 

 the kelp forest can be attributed to the presence of kelp and to the depth of the kelp forest. Located in 

 relatively deep water (15m), this kelp forest possessed an extensive midwater zone. The attraction of fish in 

 moderate densities to the midwater zone of this kelp forest contributed substantially to overall biomass. We 

 conclude that kelp per se can enhance the standing stock of fishes on a temperate reef, at least in areas of low 

 bottom relief. 



Rocky reef and giant kelp, Macrocystis pyrifera, 

 habitats off the coast of southern California support a 

 diverse and abundant assemblage of fishes (Lim- 

 baugh 1955; Quast 1968 a, b; Feder et al. 1974; Ebel- 

 ing et al. 1980 a, b). Much of the richness of this 

 ichthyofauna has been attributed to the rocky sub- 

 strate; areas with a rugose, rocky bottom and little 

 kelp seem to support more fish than areas with a flat 

 bottom and dense kelp (Quast 1968 a, b, Ebeling et 

 al. 1980a). However, kelp itself also provides a uni- 

 que habitat for some fishes (Coyer 1979; Ebeling et 

 al. 1980a) and a point of orientation in the water 

 column for others (Quast 1968 a, b; Bray 1981). The 

 kelp canopy may also serve as a nursery area for some 

 species of fish (Miller and Geibel 1973; Feder et al. 

 1974; M. Carr 3 Unpubl. data). 



Several approaches have been used to assess the 

 influence of habitat on the abundance and composi- 



1 Marine Science Institute, University of California, Santa Barbara, 

 Calif.; present address: Department of Biological Sciences, San 

 Francisco State University, San Francisco, CA 94132. 



-Marine Science Institute, University of California, Santa Barbara, 

 Calif.; present address: Marine Review Committee Research Cen- 

 ter, 531 Encinitas Boulevard, Encinitas, CA 92024. 



3 M. Carr, Moss Landing Marine Laboratories, Moss Landing, 

 CA 95039. 



tion of fish assemblages in nearshore kelp and rock 

 habitats off California. Perhaps the best analytical 

 approach is experimental, as employed by Miller and 

 Geibel (1973), Bray (1981), and Carr (footnote 3) ; 

 however, the comparative approach of Limbaugh 

 (1955; also reported in Feder et al. 1974), Quast 

 (1968 a, b), and Ebeling et al. (1980a) is also of value. 

 Based on observations in a variety of areas, Lim- 

 baugh described the habits and habitats of many 

 nearshore fishes. Quast and Ebeling et al. employed 

 broad-scale quantitative sampling of fish assem- 

 blages in different areas. Quast's interpretation of 

 data extended Limbaugh's natural history approach, 

 and added to it the actual comparison of abundances 

 in different habitats. Ebeling etal. (1980a) employed 

 a multivariate analysis of habitat characteristics and 

 relative abundances of species to define subassem- 

 blages of fishes, and also compared abundances in 

 areas of different habitat characteristics. 



In this paper we examine the abundance, vertical 

 distribution, and species composition of noncryptic 

 fishes in a forest of giant kelp near San Onofre, Calif. 

 We also report the abundance and species composi- 

 tion of fishes in a nearby area with little kelp. This 

 study, undertaken initially to predict the effects of a 



Manuscript accepted June 1983. 



FISHERY BULLETIN: VOL. 82, NO. 1, 1984. 



37 



