UREA AND OTHER NITROGENOUS NUTRIENTS IN LA JOLLA BAY 

 DURING FEBRUARY, MARCH, AND APRIL 1970 



James J. McCarthy^ and Daniel Kamykowski^ 



ABSTRACT 



Samples collected from La JoUa Bay twice weekly for 21/2 months were analyzed for 

 nitrate, nitrite, ammonium, and urea in addition to other chemical, physical, and biolog- 

 ical parameters. On the basis of an infestation of blue sharks (Prionace glauca) , periods 

 before, during, and after the infestation were defined. Statistical analyses indicated 

 that: 1) Urea concentrations were highest during the period of shark infestation. 

 2) There was strong positive correlation between phaeo-pigment/chlorophyll ratios and 

 ammonium concentrations during the infestation but none between the pigment ratios 

 and either the ammonium concentrations for the other two periods or the urea concen- 

 trations for any of the three periods. 3) There was no correlation between ammonium 

 and urea concentrations before, a strong positive correlation during, and no correlation 

 after the shark infestation. 4) Urea was the only nitrogenous nutrient for which the 

 concentrations above and below the thermocline were not different. 5) Comparisons 

 between two stations 1.5 km distant indicate that on a horizontal scale, the patch struc- 

 ture for urea is smaller than that of the other nitrogenous nutrients although the median 

 urea concentration in the water column was not different at the two stations. 



The temporal similarity and the more complex patch structure for urea (as seen in 

 4 and 5 above) suggest that the blue sharks were responsible for the higher urea con- 

 centrations during the infestation. Although the median ammonium concentrations 

 before and during the infestation were not different, the strong positive correlation 

 between ammonium and urea concentrations during the infestation hint that the sources 

 or rates of supply and utilization for both nutrients may have been closely related. The 

 strong positive correlation between phaeo-pigment/chlorophyll ratios and ammonium 

 concentrations during the infestation may imply that the source of ammonium was her- 

 bivore excretion. 



The nitrogenous plant nutrients in the marine 

 environment classically include the nitrate, ni- 

 trite, and ammonium ions. The fixation of dis- 

 solved gaseous nitrogen has been observed in 

 both the Sargasso Sea and Arabian Sea (Dug- 

 dale, Goering, and Ryther, 1964) and may for 

 certain areas be a significant process (Dugdale 

 and Goering, 1967) . More recently, evidence 

 has been presented which suggests that both urea 

 (McCarthy, 1971) and certain amino acids 



^ Institute of Marine Resources, University of Cali- 

 fornia, San Diego, La JoUa, CA 92037; present address: 

 Chesapeake Bay Institute, The Johns Hopkins Univer- 

 sity, Baltimore, MD 21218. 



^ Institute of Marine Resources, University of Cali- 

 fornia, San Diego, P.O. Box 109, La Jolla, CA 92037. 



Manuscript accepted April 1972. 



FISHERY BULLETIN: VOL. 70, NO. 4, 1972. 



(North and Stephens, 1971) may also be of im- 

 portance as nitrogenous nutrients. The purpose 

 of the present study was to compare the pattern 

 of distribution for urea with those for ammoni- 

 um, nitrite, nitrate, and other chemical, physical, 

 and biological parameters in the La Jolla coastal 

 waters. 



In contrast to the other nitrogenous nutrients, 

 little is known about the distribution, the im- 

 portance, or the cycle of either urea or amino 

 acids in marine waters. The results of quantita- 

 tive analyses for urea in a total of approximately 

 120 samples of seawater have been reported by 

 Newell (1967) and McCarthy (1970). Newell's 

 samples were collected from a depth of 10 m 

 at 25 stations in the English Channel and 45 of 



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