COVER: INVERTEBRATE ASSEMBLAGE WITH GIANT KELP 



from each replicate of each zone; for gammarid 

 amphipods, at least 50 individuals (comprising all 

 species) were measured from one randomly selected 

 replicate of each zone. Replicates were pooled and 

 size-frequency distributions were determined for 

 each taxon within each of the zones. The non- 

 parametric Kolmogorov-Smirnov (K-S) two-sample 

 test (one-tailed) was used to test whether the values 

 from one distribution were stochastically larger 

 than the values from another distribution (Siegel 

 1956). 



The mean weight of an individual within a major 

 taxon (shrimps, mysids, gammarids) was determined 

 from the mean length and the appropriate length- 

 weight formula. The mean weight then was mul- 

 tiplied by the mean monthly abundance of the taxon 

 to determine the taxon biomass. Quarterly length 

 measurements were applied to the month preceding 

 and following the measuring month (i.e., April 

 measurements were assigned to March and May) for 

 biomass measurements. Monthly abundance values 

 of the smaller taxa were multiplied by the assigned 

 weight to estimate the biomass. 



RESULTS 

 Kelp Density 



Macrocystis density at Habitat Reef was high (4.7 

 plants/m 2 ) from November 1975 through August 

 1976 (Table 2). In late September 1976, density and 

 canopy cover were reduced ( 1 .5/nr) and continued to 

 decline over the next 4 mo. 



TABLE 2. — Macrocystis density and the number of 

 fronds/plant (± width of 959? C.I./2) at Habitat 

 Reef. Sample size in parentheses. 



Date 



Density m- 



No. of fronds/plant 



General Taxonomic Composition of 

 the Invertebrate Assemblage 



The invertebrate assemblage associated with the 

 fronds of Macrocystis was composed primarily of 

 amphipods, copepods, mysids, and shrimps (Tables 

 3, 4). Mysids and shrimps were among the largest 



TABLE 4.— Mean abundance (no./kg kelp ± width of 95', C.I./2) for 

 the major invertebrate taxa within each zone. Parenthetical values 

 are the mean length and weight (mm, mg) of each taxon; an asterisk 

 indicates that a constant length and weight was used for all zones. All 

 values are averaged over the entire 19-mo study. 



Nov. 1975 

 Oct 1976 

 Dec. 1976 



4.7+2.3 (25) 

 1.5±0.7 (29) 

 0.7±0.3 (25) 



3.4±1.0(1 18) 

 6.7+1.6 (46) 

 4.7+2.6 (17) 



TABLE 3. — The mean (± width of 95' i C.I./2) monthly abundance (no. organisms/kg kelp) and 

 biomass (mg organisms/kg kelp) for each major invertebrate group associated with the giant 

 kelp. Data are averaged over the entire 19-mo study; proportions of total numbers or biomass (all 

 species) are presented in parentheses. 



57 



