FISH ASSEMBLAGES IN MACROCYSTIS AND NEREOCYSTIS 

 KELP FORESTS OFF CENTRAL CALIFORNIA 



James Lee Bodkin 1 



ABSTRACT 



The abundance and species composition of conspicuous fishes were compared within two canopy forming 

 kelp forests (giant kelp, Macrocystis pyrifera, and bull kelp, Nereocystis luetkeana) in Central Califor- 

 nia. The primary investigative method was a subtidal belt transect, in which visual observation was used. 

 The species composition of fish assemblages in the two canopy types was similar. Densities of fish were 

 generally greater in Macrocystis than in Nereocystis forests. The major difference was the density of 

 midwater species of the genus Sebastes. The blue rockfish, Sebastes mystinus, was the numerically domi- 

 nant species in both canopy types. Estimates of the biomass of fish were about 2.4 times greater in 

 Macrocystis beds than in Nereocystis beds. 



Many species of fish exhibit an affinity for substrate 

 and cover within their habitat, such as rock or coral 

 reefs or kelp beds, as well as man-made objects such 

 as piers, jetties, and offshore oil platforms. This 

 structure may provide shelter, a base for foraging 

 activity, or nursery habitat for young fish. Within 

 the temperate nearshore marine environment, 

 macroalgae may provide a large portion of this 

 substrate and cover. Kelp forests are one of the 

 major features of the nearshore environment along 

 the west coast of North America. The two most con- 

 spicuous canopy-forming kelps are the giant kelp, 

 Macrocystis pyrifera, a perennial, and the bull kelp, 

 Nereocystis luetkeana, an annual (Abbott and 

 Hollenberg 1976). Besides the difference in peren- 

 nial versus annual growth pattern, Macrocystis and 

 Nereocystis differ markedly in physical structure 

 (Fig. 1) and seasonal patterns of abundance. Macro- 

 cystis plants typically have many stipes originating 

 from a single large holdfast, and large fronds at- 

 tached to each stipe throughout its length. Nereo- 

 cystis plants consist of a single stipe, with large 

 fronds only at the distal end. During periods of full 

 development (typically late summer), Macrocystis 

 can develop a completely closed canopy, whereas 

 Nereocystis typically has a broken canopy. Winter 

 storms usually remove large portions of the Macro- 

 cystis canopy, but many plants remain secured to 

 the substrate and provide structure within the water 

 column to varying depths throughout the year. 

 Nereocystis canopies are also typically removed dur- 



iU.S. Fish and Wildlife Service, P.O. Box 70, San Simeon, CA 

 93452. 



ing these storms, and, because Nereocystis is an 

 annual, it provides little or no structure from mid- 

 winter through late spring. 



Nereocystis may be more abundant than Macro- 

 cystis in the presence of severe and persistent 

 disturbances such as continued exposure to large 

 swells or heavy grazing pressure (Dayton et al. 

 1980). In the absence of this pressure, Macrocystis 

 may be competitively dominant, in that it forms a 

 dense and often complete surface canopy earlier in 

 the year, and thus may exclude or limit Nereocystis 

 which has light-sensitive germination requirements 

 (Dayton et al. 1980, 1984). 



This study was designed to test the hypothesis 

 that the fish component of the Macrocystis pyrifera 

 community differs from that of the Nereocystis luet- 

 keana community in Central California. 



METHODS 



Studies were conducted from 6 km south to 15 km 

 north of Point Piedras Blancas, San Luis Obispo 

 County, CA (lat. 35°40'N, long. 121°17'W) (Fig. 2). 

 Additional studies were also done near Big Creek, 

 Monterey County, CA Gat. 36°04'N, long. 121°36'W). 

 The surface canopies of kelp beds consist almost ex- 

 clusively of Nereocystis from Point Piedras Blancas 

 north to Ragged Point, an area about 13 km long, 

 but are dominated by Macrocystis south of Piedras 

 Blancas. I searched 74 transects in the Piedras 

 Blancas study area and 4 in the Big Creek area: 26 

 transects in Macrocystis forests and 14 in Nereo- 

 cystis in 1982 and 17 in Macrocystis and 21 in Nereo- 

 cystis in 1983. Field studies extended from June 



Manuscript accepted March 1986. 



FISHERY BULLETIN: VOL. 84, NO. 4, 1986. 



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