OFEF SITE SELECTION CRITERIA 



BIOLOGICAL REQUIREMENTS/LIMITATIONS 



Site selection criteria dealing with the biological requirements and limitations are 

 summarized in Table 1 . 



Nutrients 



Surface waters of the open ocean in temperate and tropical areas beyond coastal 

 and upwelling influences are generally nutrient-limited to the degree that the naturally 

 available nutrients will sustain only low levels of productivity. It has been demonstrated 

 that nitrogen is the principal controlling nutrient in the eastern tropical Pacific (Refs. 4 and 

 5) and is the primary nutrient limiting growth of phytoplankton off southern California 

 (Ref. 6). 



Studies of marine macroalgae productivity as a function of nutrient concentration 

 are few. Waite and Mitchell (Ref. 7) have demonstrated that increases in the concentration 

 of ammonia and phosphate significantly increase the rate of carbon fixation (photosynthesis) 

 in Ulva lactuca , a green macroalgae. In the red alga Eucheuma , periods of maximum growth 

 coincide with maximum nutrient concentrations during periods of lowered temperatures and 

 reduced light along the Florida coast (Ref. 8). 



Jackson states in his PhD thesis that for natural kelp beds ( M. pyrifera) off San Diego 

 "the condition most hmiting Macrocystis production was the low concentration of dissolved 

 nutrients, especially nitrogenous substances, near the surface" (Ref. 9). Nitrate concentra- 

 tions in the San Diego Point Loma kelp bed were generally low, less than 1 ;ug-at/hter 

 NO3 - N* (Ref. 9), however, during upweUing periods can go as high as 5.8 jUg-at in the near- 

 surface (Ref. 10). There is evidence that M. pyrifera compensates for this nitrogen hmitation 

 by translocating it from depths where concentrations are significantly higher (Ref. 9). This 

 characteristic is very significant and should be considered when designing the upwelling and 

 distribution systems for the Ocean Farm. 



Natural populations of M. pyrifera off southern Cahfornia experience nitrate concen- 

 trations on the surface from near ptg-at/hter to as high as 9 /ig-at/hter NO3-N, but generally 

 less than 4 /zg-at/liter. At 8-10 meters depth the concentrations are usually higher, varying 

 from about 1 /xg-at to as high as 16 with a mean range of 2-6 Mg-at NO3-N (Refs. 9 through 

 1 2). Nutrient concentrations are usually highest in the January to June period and lowest in 

 late summer. Growth rates have been observed to be decidedly low when dissolved nitrogen 

 falls below 1.0 Mg-at/hter (Ref. 13). Preliminary studies by W. North indicate that Kj^ for 

 NO3 (the concentration of nitrate at which the uptake velocity of nitrate is 1/2 maximum) 



is near 9.4 Mg-at/liter (Ref. 13). Optimally, the concentration of nutrients should be above 

 the Kjj^ for maximal productivity. An area having a 10-15 /xg-at/liter NO3-N should yield a 



very high growth rate. Above this concentration the uptake rate curve levels off, therefore. 



*/ ng-at litter NO ^N =14 micrograms nitrate nitrogen/liter or 14 parts per billion (ppb). 



