Gerard (1982c) also found evidence 

 that at high concentrations of N0 3 " (25 

 uM), nutrient uptake was saturated at 

 relatively low current velocities (2.5 

 cm/sec). Furthermore, she found that 

 water surge and movement of plant surfaces 

 in the water column were sufficient to 

 saturate uptake, even in a dense 

 Macrocystis forest with calm sea 

 conditions and low current velocity. 



Nutrients may, 

 different effects on 

 stages of plants, and 

 related to season, 



therefore, have 



the various life 



this may also be 



stratification of 



nitrogen, and water motion. 



The effects of light, temperature, 

 nutrients, and their interactions have 

 only just begun to be studied. Better 

 field studies must be devised which can 

 measure variability at different scales. 

 For example, nutrients may have effects on 

 a small scale within a kelp forest; there 

 may also be wery broad-scale effects over 

 portions of the forests, or the entire 

 kelp stand. Fronds on a single plant show 

 variability in growth rates and nutrient 

 uptake, but there is also variability 

 among plants of the same age, exposed to 

 similar environmental conditions. 

 Experiments must be able to quantify these 

 various levels of variability. Also, 

 there is a need for careful controls with 

 which to compare translocated or 

 experimental kelp plants. 



One type of experiment needed is a 

 laboratory study examining different 

 levels of light, temperature, and 

 nutrients (see Table 11). Such a design 

 will allow some measure of main effects 

 and the importance of interactions. This 

 experiment is currently being done by 

 Deysher and Dean (pers. comm.). 



These are central issues in the 

 controversy of what produces "good years" 

 and "bad years" for Macrocystis . Why is 

 recruitment greater at some times and why 

 are canopies more lush in different years? 



5.5 EFFECTS OF COMPETITION 



5.5.1 Canopy Removals 



General Hypotheses: (1) Competitive 

 interactions among species affect the 

 local-scale distribution and abundances of 

 individual species. (2) Bare primary 

 substratum significantly increases the 

 recruitment of large brown algae. 



The most common method used to 

 determine the effects of one algal species 

 on another is the selective removal of 

 algal canopies and the subsequent 

 recording of which species either 

 persisted in or recruited to the areas. 

 Dayton (1975) removed canopies of several 

 species at different depths at a site in 

 Alaska. Five hypotheses were tested, each 



Table 11. Outline of an example of a factorial laboratory experiment to assess the 

 importance of light, temperature and nutrients, and their interactions, on gametophyte 

 growth, fertility and the production of sporophytes. The design uses three levels for 

 each factor: nutrients, light, and temperature. Number of replicates determined from 

 initial trials and desired statistical power. 



Nutrient 



Nutrients 1 



Nutrients 2 



Nutrients 3 



Light Light 1 Light 2 Light 3 Light 1 Light 2 Light 3 Light 1 Light 2 Light 3 

 Temperature Tl T2 T3 Tl T2 T3 Tl T2 T3 Tl T2 T3 Tl T2 T3 Tl T2 T3 Tl T2 T3 Tl T2 T3 Tl T2 T3 

 Replicates 1. 



2. (for each T) 



3. 



97 



