Habitat Groups and Island-Mainland Distribution of Kelp-bed Fishes off Santa Barbara, CA

INTR()DUCTION The islands off southern California diversify the coastal environment by doubling the length uf shoreline and extending coastal habitats (Hom 1974). Geologically, and perhaps biologically. these islands may be classified into northern (bordering the Santa Barbara Channel) and southern groups (Hewatt 1946, Valentine and Lipps 1967. Weaver and Doerner 1967). Yet classification of the insular shore fish fauna is more complex. On a broad scale, distributions of shore fishes are influenced by water temperature and associated currents: the cool, southerly/lowing California Current offshore, and the warmer, inshore countercurrent and eddy (Hubbs 1967,1974, Neushul et al. 1967). Also, the specific assemblage of fishes in a given area will depend very strongly on the habitat structure there. And finally, isolation at islands may be hrought about either by differential transport of species having planktonic larvae (Kanter 1980, Seapy and Littler 1980) or by chance transport of species that have no planktonic dispersal stage (if. Haldorson 1980). Our study analyzes the effects of habitat on the composition of one element of the inshore fish fauna, the kelp-bed fishes, and applies this analysis to compare the kelp-bed fish assemblages at Santa Cruz Island with those from the adjacent Santa Barbara mainland. Some papers in this symposium dealt with large-scale biogeography of inshore organisms on Ihe Califomia Islands (Seapy and Littler 1980, Silva 1978). Even though we do not address this problem directly, we realize that interpretations of habitat effects must consider geographic affinities of the fauna. On the other hand, habitat effects may confound broad-scale geographic effects (cf. Kanter 1980, Littler 1980). Our objective, therefore, is to show how assemhlages of kelp-bed fishes may be classified into particular habitat groups, and how differences in siructural habitat affect the composition of fish assemblages making up such groups. We did our study off Santa Barbara, at the southern end of a transitional zone between a warm-temperate biota to the southeast and a cool-temperate biota at San Miguel Island and north of Point Conception (if. Hewatt 1946, Hubbs 1948, 1960, 1974, Neushul et (//. 1967. Quast 1968b, Ebelinget al. 1971). The mixed composition of the fauna rellects water temperalure and exposure to currents. The California Current carries cool water seaward past Point Conception, although a small branch of this current feeds a counterclockwise eddy in the Weslern part of the Santa Barbara Channel (Reid 1965, Kolpack 1971). This eddy meets warmer Currents from the southeast at the eastern end of the Channel, near Santa Barbara and Sanla Cruz Island (Kolpack 1971). Therefore, even though oceanographically complex. our sludy areas are warmer and more exposed to southern currents than is San Miguel Island al the \I'estern end of the channel.