BODKIN: MACROCYSTIS AND NEREOCYSTIS KELP FORESTS 



of Macrocystis in water up to 4 m deeper than that 

 occupied by Nereocystis within the study area, the 

 mean water depth at which surveys were made dif- 

 fered between sites (Macrocystis mean depth =12.2 

 m; Nereocystis mean depth = 10. 5m, t = 2.73, P 

 = 0.008 (two sample £-test)). When the five transects 

 in Macrocystis which occurred at depths beyond the 

 maximum depth of Nereocystis transects (16 m) 

 were excluded from analysis, the difference in water 

 depths between sites became insignificant. Follow- 

 ing the removal of these deep transects, all species 

 of fish, both midwater and benthic, were reevalu- 

 ated. There were no changes in the results presented 

 above following this treatment. 



There was little correlation between densities of 

 fish and either of the bottom relief indices (r values, 

 0.025 to 0.482). Throughout the study, bottom relief 

 typically ranged from 1 to 4 m and relief <1 m was 

 not encountered. Mean values of the objective relief 

 index were 44.1 (SE = 2.8) for Macrocystis tran- 

 sects and 37.2 (SE = 2.2) for Nereocystis transects. 

 This difference resulted in a P value of 0.061 (two 

 sample £-test), which I considered significant. How- 

 ever, when all species of fish which demonstrated 

 significantly different densities between canopy 

 types were reevaluated, after excluding the six 

 Macrocystis transects with relief values more than 

 one standard deviation above the mean, no change 

 in results was observed for any species tested. 



The total number of species encountered on the 

 transects was 26 in Macrocystis and 23 in Nereo- 

 cystis. The two kelp forests had 22 species in com- 

 mon. Five species were found in only one of the two 

 canopy types, although none of these were present 

 in more than 21% of the transects within the canopy 

 in which it was found. The H' values calculated were 

 1.76 for Macrocystis transects and 1.58 for the 

 Nereocystis transects. Although the value of diver- 

 sity indices has been questioned (Goodman 1975), 

 such indices are widely used in ecological literature. 

 Neither measure of diversity used in the present 

 study indicated differences in the diversity of fish 

 assemblages between the two kelp forest types 

 investigated. 



DISCUSSION 



Several measures of comparison were considered 

 in the analysis of these two kelp communities: 

 species composition, species diversity, and abun- 

 dance of fishes. The data presented here demon- 

 strate very little difference in either composition or 

 diversity of fish assemblages (Table 1), while esti- 

 mates of biomass were markedly higher in giant kelp 

 compared with bull kelp (Table 4). 



The single most obvious difference between the 

 two kelp communities was in the abundance of the 

 blue rockfish: mean density of fish (no./lOO m 2 ) was 



Table 4.— Estimates of biomass of fish of Macrocystis and Nereocystis kelp forests. Species that were uncommon, (<20% 



of transects), or small are not included. 



'Mean weights from collections at Piedras Blancas Field Station, U.S. Fish and Wildlife Service, or estimated from mean total lengths. 



805 



