There is some information on density 

 effects for Macrocystis . North (1971c) 

 used three stands of different densities 

 to examine growth rates of fronds. He 

 found that the stand at highest density 

 had plants which grew slightly faster than 

 those at other densities, but attributed 

 this result to unknown "localized 

 factors." 



Neushul and Harger (in press) planted 

 adult Macrocystis (mean size of 25 fronds 

 per plant) at different densities on a 

 test farm near Santa Barbara, California. 

 The densities used were 1 plant/m 2 , 1 

 plant/4 m 2 and 1 plant/16 m 2 . The results 

 indicated that plants at the lowest 

 density had the most fronds and greatest 

 weight after a year, while the highest 

 density plants fared the poorest. Their 

 results suggest that shading in the denser 

 parts of the stand caused the poorer 

 growth. Possible complicating factors in 

 this experiment were: (1) the initial use 

 of adult plants, which may already have 

 adapted to a particular growth regime; (2) 

 the logistic constraint of using only one 

 small experimental plot (0.24 hectares) 

 with the different densities being 

 contiguous; and (3) the placement of low 

 and medium density plants toward the 

 outside of the stand where peripheral 

 light may have affected growth. Their 

 experiment, however, forms a useful basis 

 for selecting planting densities for the 

 purpose of mariculture (see Chapter 6). 



Mortality may also be affected by the 

 density of stands. Work in both central 

 and southern California has indicated that 

 the major source of mortality for large 

 Macrocystis plants is entanglement with 

 drifting plants (Rosenthal et al . 1974, 

 Gerard 1976). Large bundles of drifting 

 plants may accumulate and remove more 

 plants from the kelp forest during periods 

 of increased water motion. 



Intraspecific competition for light, 

 nutrients, and space may prove to be 

 important in large brown algal systems. 

 Testing for these effects requires 

 experiments which control for the ages of 

 plants, habitats, depths, and localized 

 factors associated with sites. These 

 experiments can take the form of thinning 

 experiments, whereby areas with high 

 recruitment have treatments thinned to 



lower densities. High recruitment into an 

 area indicates that it is suitable, at 

 least for the initial life stages of the 

 alga. If different density treatments are 

 contained in the area of initially high 

 recruitments, site effects will be 

 reduced. Another way to approach this 

 problem is to outplant sporophytes at 

 differing densities, and record subsequent 

 growth and survival. 



It has been suggested for some 

 species in the Fucales that higher 

 densities of adult plants result in 

 release en masse of gametes, which may be 

 important for good recruitment (Fletcher 

 and Fletcher 1975, Schiel 1981). Greater 

 densities may also be important to effect 

 successful fertilization of gametophytes 

 (that is, for males to find females). 

 There is little information on these early 

 life stages and density for Macrocystis . 



Macrocystis forests may be extensive 

 in size, with relatively high densities of 

 plants and virtually 100% cover of the sea 

 surface by algal fronds. Little is known 

 about the importance of "patch size" to 

 the growth, eventual sizes of plants, and 

 reproduction. Macrocystis in small 

 patches, such as artificial reefs, tend to 

 suffer rapid deterioration and mortality 

 due to fish grazing (LOSL 1983). The 

 effects and importance of patch size can 

 be tested, and are relevant to attempts at 

 establishing algal populations where they 

 do not presently occur. 



5.5.3 Spore Dispersal 



General Hypothesis: The distribution 

 of algal spores or their differential 

 mortality account for the distribution of 

 adult plants. 



The problem of determining whether 

 spores have actually arrived to an area is 

 important to arguments about competition 

 among species (Denley and Dayton in 

 press). There is increasing evidence that 

 spore or germling dispersal is limited for 

 many brown algal species, with most 

 recruits appearing within a few meters of 

 reproductive adult plants (Anderson and 

 North 1966; Dayton 1973; Paine 1979; 

 Schiel 1981, in press b; Deysher and 

 Norton 1982). The problem of whether 

 algal germlings can survive and grow in 



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