FISHKRY BULLETIN: VOL. 82, NO. 1 



MATERIALS AND METHODS 

 Zonation and Kelp Density 



The kelp forest at Habitat Reef was divided into 

 three vertical zones: Canopy (C), middle (M), and 

 bottom (B). The canopy extended from the water sur- 

 face to a depth of 1 m, the bottom ranged from just 

 above the kelp holdfasts to 2 m above the substrate, 

 and the middle included the area between the canopy 

 and the bottom. Holdfasts were not examined. Kelp 

 density was measured by randomly establishing 25 

 circular 1 m : plots within the study area during 

 November 1975 and October and December 1976. 

 The number of enclosed plants and the number of 

 fronds/plant were determined. 



Sampling Procedure 



Samples were collected monthly from plants in the 

 central portion of the kelp forest (7-9 m depth) during 

 tidal heights ranging from +1.0 to +1.3 m mean 

 lower low water. From June through September 



1975, three replicate samples were collected from 

 each zone; from October 1975 through December 



1976, five replicates were collected. Only one sample 

 was collected from any plant, and this sample con- 

 sisted of the entire plant portion within the desired 

 zone. The middle and bottom zones were collected 

 by carefully severing the upper portions and allow- 

 ing them to drift away. Disturbance to the lower 

 zones during this procedure was negligible. Similar 

 amounts of kelp were collected from each zone 

 throughout the study (n = 19; kg = 2.5[C] 2.1[M], 

 2.3 [B]). 



The kelp-associated invertebrates were collected 

 by scuba divers maneuvering a plankton net (1 m 

 diameter, 3 m long, 0.33 mm mesh) over the desired 

 portion of the plant. This procedure captured most 

 motile invertebrates on the kelp, as well as within the 

 surrounding water column (1 m diameter). The 

 enclosed sample was placed in a large container filled 

 with warm freshwater (providing a thermal and 

 salinity shock), vigorously agitated, and removed. 

 The remaining water was filtered through a 0.25 mm 

 sieve and the residue preserved. Thus, the term "in- 

 vertebrate" in this investigation refers to all motile 

 individuals larger than 0.33 mm (excluding pro- 

 tozoans, cnidarians, and nematodes). 



The efficiency of the agitation-freshwater method 

 was tested by placing the processed kelp into another 

 container of warm freshwater and allowing it to stand 

 for 4 h. Subsequent agitation and filtering indicated 

 that 96% of all motile invertebrates in each zone were 



removed by the initial agitation-freshwater treat- 

 ment. 



Organisms were identified to species (except for 

 some juveniles). The wet weight of kelp from each 

 sample was measured, and abundances of all taxa 

 were expressed as the number of individuals per 

 kilogram (wet weight) of kelp. The somewhat uncon- 

 ventional normalization of species abundance to unit 

 biomass was selected for three reasons. First, struc- 

 tural complexity within the kelp forest habitat is 

 created by interdigitating kelp blades and stipes and 

 is a function (in part) of both kelp surface area and 

 biomass. Many kelp-associated species, particularly 

 the swarming mysids, may respond primarily to 

 structural complexity of the habitat when seeking 

 shelter and/or food. Secondly, biomass is much 

 easier and faster to measure than is surface area (con- 

 version ratios of kelp wet weight to surface area [both 

 sides of blades + stipes] and kelp dry weight to wet 

 weight are presented in Table 1). Thirdly, unit 

 biomass will facilitate comparisons with invertebrate 

 associations of other species of marine algae for 

 which it is difficult to compute a unit area (i.e., bushy 

 reds and browns). 



TABLE 1. — Ratios of kelp wet weight (kg) to kelp surface 

 area (rrr) and dry weight (kg) to wet weight (kg). 



Determination of Invertebrate 

 Lengths and Biomass 



Growth series within the principal taxa were 

 established. Individuals (n = 30-94) were measured 

 to the nearest 0.04 mm, using a dissecting micro- 

 scope and occular micrometer, blotted dry, and 

 weighed using an analytical balance to determine 

 length-weight relationships. Smaller and/or minor 

 taxa (copepods, ostracods, caprellids, molluscs, etc.) 

 were assigned constant weights based on the mean 

 weight of 20 individuals. 



Vertical patterns of size-stratification were ex- 

 amined by measuring the lengths of principal taxa 

 within each zone for each quarter from January 

 1975 through October 1976. Single samples were 

 collected in January and April 1975; subsequent 

 samples were replicated (3 or 5). For shrimps and 

 mysids, all (January through July 1975) or up to 75 

 individuals of each major species were measured 



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