providing the plants with greater than 15 /zg-at-N03-N would probably not be economical 



(e.g., an increase from 16 to 23 jug-at/liter only causes an increase in uptake rate of 12 per- 

 cent, Ref. 13). Minimum levels of NO3 required for the marine farm are estimated to be 

 between 3 and 5 /ag-at/liter (an increase in uptake rate of 400 percent is computed when 

 NO3 levels are increased from 1 to 5 ^ug-at/liter from W. North data, Ref. 13), since average 



levels of NO3 off the southern California coast at depths between 1 00 and 300 meters vary 



from 15 to 30 /ig-at/liter. If the nitrate required by M. pyrifera is between 3 and 1 5 Mg"at/ 

 liter, then the estimated amount of upwelled water to provide this level of nutrient to the 

 plants is between 10 and 50 percent assuming thorough mixing of upwelled with surface 

 waters. A very important parameter discussed by North (Ref. 13), is the percentage of 

 surface area of kelp that is exposed to given levels of NO3. This factor should be considered 



in the design of the distribution system. If exposure area on the M. pyrifera can be maxi- 

 mized, then the concentration of NO3 might be reduced significantly while maintaining 

 adequate growth rates. 



Temperature 



In most biochemical systems, increases in temperature cause increases in chemical 

 reaction rates to some maximal temperature level beyond which inhibition occurs. Tempera- 

 ture is found to be very important in modifying kelp growth rate. Comparison of elongation 

 growth rates measured at different temperatures yield a Q\q* of approximately 1.7 for 



M. pyrifera (Ref. 14). This indicates that the expected increase in frond elongation for a 

 10°C rise in temperature is by the factor 1 .7. However, M. pyrifera off southern Cahfornia 

 does poorly at temperatures above 20°C, and when above 25°C the symptoms of "tempera- 

 ture damage" (pigment loss, brittleness, sloughing) appear in a week or less (personal com- 

 munication, W. North). 



Clendenning studied the effect of short-term exposures to high temperatures and 

 found that light-saturated photosynthesis was always highest between 20° and 25°C 

 (Ref. 15). At 30°C photosynthesis was completely inactivated within the first hour of 

 exposure in kelp collected from depths of 15 to 20 meters, and it was partially inactivated 

 in one hour in kelp collected from the surface canopy. In longer term experiments at 

 23.9°C (75°F). M. pyrifera showed a decrease in photosynthetic capacity after one day and 

 severe degradation of the plant after two days (Ref. 1 5). M. pyrifera from Bahia Tortugas, 

 Baja California, flourishes in water that reaches approximately 26°C for several weeks during 

 late summer (W. North, personal communication). Clendenning demonstrated that the 

 photosynthetic temperature optimum for the Turtle Bay kelp was between 25° and 30°C. 

 These plants also exhibited a 50-percent-higher photosynthetic capacity per unit area than 

 has been observed in local southern California kelp (Ref. 15). 



Studies on the effect of temperature on M. pyrifera growth have not generally 

 included nutrient measurements. In the reported cases where there has been a summer 

 die-off of kelp, allegedly caused by higher than normal temperatures, nutrient data are 



*Temperature coefficient. The increase in rate of a process (expressed as a multiple of initial rate) produced by raising the 

 temperature 10° C. 



