FISHERY BULLETIN: VOL. 84, NO. 4 



15.0 in Macrocystis and 3.9 in Nereocystis. Blue 

 rockfish probably are the largest contributor to the 

 total biomass of kelp forest fish communities in Cen- 

 tral California. Miller and Geibel (1973) estimated 

 blue rockfish densities at 6.66 fish/100 m 2 in 1969 

 and 8.35 in 1970 in Macrocystis beds at Hopkins 

 Marine Life Refuge, Monterey County, CA. They 

 suggested that this represents about 50% of the ac- 

 tual biomass because their survey method under- 

 represented midwater species. Considering this ad- 

 justment, my data for blue rockfish in Macrocystis 

 forests agree well with theirs. Near Pt. Piedras 

 Blancas, blue rockfish made up 33% and 18% of the 

 mean number of fish within the Macrocystis and 

 Nereocystis forests, respectively. Assuming an aver- 

 age weight of 440 g (Table 4), blue rockfish con- 

 tributed about 70% of the total biomass of the 

 Macrocystis fish assemblage and about 50% of 

 Nereocystis (species weighing a few ounces or less 

 were not included in this analysis). The importance 

 of juvenile blue rockfish as forage for large car- 

 nivorous kelp forest fishes (primarily Sebastes sp.) 

 has been well documented (Miller and Geibel 1973; 

 Burge and Schultz 1973; Hallacher and Roberts 

 1985). Tagging studies have suggested that the 

 home range of blue rockfish is relatively small (Miller 

 and Geibel 1973). The evidence given here illustrates 

 the important role that blue rockfish play in the kelp 

 forest communities of central California. 



My estimate of the biomass of fish within each of 

 the two canopy types (Table 4) included only species 

 that were relatively common and of sufficient size 

 to contribute significantly to the total. For exam- 

 ple, although the estimated mean weight of Oxyjulis 

 californica was only 24 g, its abundance made its 

 total contribution rather large. 



My data showed that in this study area off Cen- 

 tral California Macrocystis supported a larger stand- 

 ing crop of fish, primarily midwater species of the 

 genus Sebastes, than did forests of Nereocystis 

 (Table 4). The following explanations are offered for 

 the observed differences. These explanations are not 

 mutually exclusive; several or all of the proposed ex- 

 planations may have contributed to the observed 

 patterns. 



1) The amount of algae consumed by blue rock- 

 fish fluctuates seasonally. Hallacher and Roberts 

 (1985) showed that blue rockfish may use algae as 

 a major source of energy during the non-upwelling 

 period (September through March), which partly 

 coincides with the period of minimum development 

 in Nereocystis forests. During this period blue rock- 

 fish may rely on Macrocystis directly as a food 



source, or indirectly as a substrate from which in- 

 vertebrates are taken. The resulting increased 

 biomass of blue rockfish in Macrocystis may help 

 support larger numbers of other carnivorous fish. 

 Four of the seven species that were densest in 

 Macrocystis (Table 5) forests are known to rely 

 heavily on juvenile rockfish for food (Hallacher and 

 Roberts 1985). Although juvenile rockfish densities 

 were not statistically greater in the Macrocystis 

 forest (Table 2) because of large variations in den- 

 sities (occurring on transects in either very large or 

 very small schools), they were generally more avail- 

 able in Macrocystis forests. Subsequent field obser- 

 vations of juvenile rockfish in central California kelp 

 forests have indicated that kelp forest rockfish 

 recruitment may have been poor during the course 

 of this study. 



Table 5. — Summary of species for which densities in the two kelp 

 types differed significantly. 



Species 



Canopy type which presented 

 significantly higher density 



Midwater 

 Sebastes mystinus 



Blue rockfish 

 Sebastes serranoides 



Olive rockfish 

 Sebastes atrovirens 



Kelp rockfish 

 Sebastes melanops 



Black rockfish 

 Benthic 

 Sebastes carnatus 



Gopher rockfish 

 Embiotoca lateralis 



Striped seaperch 

 Oxylebius pictus 



Painted greenling 

 Sebastes atrovirens 



Kelp rockfish 



Macrocystis 



Macrocystis 



Macrocystis 



Observed on Macrocystis mid- 

 water transects only 



Macrocystis 



Macrocystis 



Macrocystis 



Macrocystis (considered primarily 

 as a midwater species) 



2) The perennial nature of Macrocystis forests 

 compared with the annual nature of Nereocystis 

 forests may contribute to increased fish densities 

 in Macrocystis forests. Macrocystis forests provide 

 some structure throughout the year with new 

 growth providing both vertical and canopy structure 

 1 to 3 mo earlier than Nereocystis. This temporal 

 stability may afford necessary habitat structure 

 within the water column permiting relatively higher 

 densities of fish. 



3) Differences in abiotic factors such as the 

 physical orientation of the reef systems to oceanic 

 swells and the resultant surge and scour effects may 

 play a role in determining habitat suitability for 

 some species of fish. The effects of sediment trans- 

 port and scouring, caused by water movement, 



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