(1973), we could find no published data on 

 the biomass of mobile invertebrates, even 

 though these animals can be quite abundant 

 and trophically important (see below). As 

 Table 4 shows, Macrocystis biomass can 

 vary by more than an order of magnitude. 

 This variation is probably the result of 

 differences in sampling methods and sample 

 size (few samples in a patchy 

 environment), differences in sampling 

 times, and real differences within and 

 among kelp forests. Gerard's (1976) data 

 are most representative of a single site 

 as she sampled over 2.5 years in the same 

 area, and found that giant kelp biomass 

 varied from 0.7 to 6.3 wet kg/m 2 (mean = 

 3.5). This large within-forest variation 

 for Macrocystis (and, when determined, 

 other groups of organisms as well; see 

 below) clearly indicates that one sampling 

 cannot characterize biomass in these 

 spatially and temporally variable 

 communities. 



The values for Macrocystis can be 

 compared with other temperate nearshore 

 kelp communities. Kain's (1979) review of 

 Laminaria spp. suggests the "typical" 

 biomass of this genus in Laminaria beds is 

 -v. 10 wet kg/m 2 (range 2.5-20). Similar 

 values have been found for mixed 

 Ecklonia - Laminaria beds in South Africa 

 (Vel imirov et al. 1977; see review in Mann 

 1982). 



The biomass of understory vegetation 

 also varies considerably (Table 4). For 

 these plants, the data of Breda (1982) 

 from two sites in central California are 

 most indicative of possible seasonal 

 variation at a single site: an order of 

 magnitude in one year. However, these 

 relatively long-term studies by Gerard 

 (1976) and Breda (1982) were done in cen- 

 tral California where, as discussed in 

 Section 3.5, storm-related variability 

 appears to be greater than in southern 

 California. As for percentage cover (see 

 Section 2.4), understory algal biomass is 

 usually lower beneath than away from a 

 giant kelp canopy (North 1971b, Aleem 

 1973) and, in the absence of a canopy, 

 generally decreases with depth (Aleem 

 1973). 



Few estimates of the biomass of 

 sessile benthic invertebrates or fish have 

 been made (Table 4), and none over long 



periods of time. Miller and Geibel (1973) 

 suggested that their relatively high fish 

 estimates for central California versus 

 those for southern California (Table 4) 

 could be due to differences in sampling 

 methods. 



3.6.3. Primary Productivity 



Macrocystis pyrifera is a large plant 

 with a complex morphology and its primary 

 productivity is difficult to measure. A 

 variety of techniques, including field 

 harvests (Clendenning 1971b), growth 

 measurements (Gerard 1976), changes in 

 oxygen content of forest water (McFarland 

 and Prescott 1959, Jackson 1977), field 

 measurements of radioactive carbon uptake 

 (Towle and Pearse 1973), and extrapola- 

 tions from laboratory measurements 

 (Wheeler 1978) have been used to estimate 

 the productivities in Table 5. No doubt 

 some of the variability in Table 5 is the 

 result of technique (suggested by the 

 greater similarity of estimates using the 

 same technique). 



Again, because of the long-term 

 nature of the study, Gerard's (1976) data 

 are perhaps most representative of true 

 productivity, even though she did not 

 account for grazing, detrital, or 

 dissolved organic matter losses (see 

 Section 3.6.4 below). Based on frond 

 addition and growth measurements, Gerard 

 (1976) found monthly productivity to vary 

 between 0.4 and 3.0 wet kg/m 2 , with an 

 average of 23 wet kg/m 2 /yr. Using the 

 conversion factors from Coon (1982) given 

 in Table 5, this is equivalent to 2.8 kg 

 dry wt., or 530 g C(carbon)/m 2 /yr. 

 However, there is some disagreement 

 between conversion factors for wet weight- 

 carbon as Towle and Pearse (1973) use a 

 factor of 0.036. With this higher value, 

 Gerard's (1976) productivity is 828 g 

 C/m 2 /yr. In either case, these values are 

 within the range of the more productive 

 marine macrophyte communities (Mann 1973, 

 1982). Macrocystis biomass can also turn 

 over rapidly ("productivity [23 wet 

 kg/m 2 /yr]/biomass [3.5 wet kg/m 2 ] 

 turnover of 6.6 times/yr). 



Mann (1982, pp. 59 and 60) suggested 

 that large kelps like Macrocystis should 

 have a low P/B (productivity/biomass) 



37 



