McCarthy and kamykowski: urea and other nitrogenous nutrients 



of urea (Corner and Newell, 1967; McCarthy, 

 1971) so the lack of correlation with phaeo-pig- 

 ments might further implicate the blue sharks 

 as the major source of urea during Period B. 

 The residence times of ammonium and urea may 

 well differ since ammonium is utilized readily 

 by all marine phytoplankters whereas urea is 

 utilized by only some species and even then up- 

 take may be partially suppressed by certain con- 

 centrations of nitrate or ammonium (McCarthy 

 and Eppley, in press) . It is not known whether 

 urea is released in fecal pellet degradation. 



The data from the present study do not show 

 whether the relationship between the presence 

 of the blue sharks and the elevated urea values 

 in Period B is one of cause and effect. If the 

 sharks were a significant source of urea, this 

 may provide an explanation for the similarity 

 in urea concentrations above and below the ther- 

 mocline, the more irregular distribution of urea, 

 and perhaps the lack of correlation between 

 phaeo-pigment/chlorophyll ratios and urea con- 

 centrations. Without estimates of urea input 

 due to excretion by sharks, other fish, zooplank- 

 ton, and possibly birds, and rates of urea util- 

 ization for phytoplankton, the net effect of the 

 shark population's contribution to urea produc- 

 tion cannot be rigorously evaluated. 



While this manuscript was in review, Remsen 

 (1971) published the results of urea analyses 

 for samples collected from both the eastern trop- 

 ical Pacific Ocean and coastal waters off north- 

 eastern United States. The concentrations he 

 detected were generally higher than those re- 

 ported either previously or in this communica- 

 tion but his conclusions as to the biological sig- 

 nificance of urea in the marine environment are 

 not at variance with those presented here 



ACKNOWLEDGMENTS 



We wish to thank Drs. R. W. Eppley, E. W. 

 Eager, and M. M. Mullin for their valuable ad- 

 vice and encouragement and Dr. F. P. Shepard 

 for the permission to use his map of La Jolla Bay. 



This work was supported by Federal Water 

 Quality Administration Grant 16010 EHC to 

 R. W. Eppley; United States Atomic Energy 

 Commission Contract AT (11-1) GEN 10, P.A. 



20, R. W. Eppley, principal investigator; and Of- 

 fice of Naval Research Contract N00014-69-A- 

 0200-6006. 



LITERATURE CITED 



Baldwin, E. 



1964. An introduction to comparative biochemistry. 

 4th ed. Cambridge Univ. Press, Lond., 179 p. 



Barnes, R. D. 



1963. Invertebrate zoology. Saunders, Phila., 

 632 p. 



Beers, J. R., and A. C. Kelly. 



1965. Short-term variation of ammonia in the 

 Sargasso Sea off Bermuda. Deep-Sea Res. 12: 

 21-25. 



Bendschneider, K., and R. J. Robinson. 



1952. A new spectrophotometric method for the 

 determination of nitrite in sea water. J. Mar. 

 Res. 11:87-96. 



BOYLAN, J. W. 



1967. Gill permeability in Squalus acanthias. In 

 P. W. Gilbert, R. F. Mathewson, and D. P. Rail 

 (editors), Sharks, skates and rays, p. 197-206. 

 Johns Hopkins Press, Baltimore. 

 Carlucci, A. F., E. 0. Hartwig, and P. M. Bowes. 

 1970. Biological production of nitrite in seawater. 

 Mar. Biol. (Berl.) 7:161-166. 

 Carritt, D. E., and J. H. Carpenter. 



1966. Comparison and evaluation of currently em- 

 ployed modifications of the Winkler method for 

 determining dissolved oxygen in seawater; a 

 NASCO Report. J. Mar. Res. 24:286-318. 



Corner, E. D. S., and B. S. Newell. 



1967. On the nutrition and metabolism of zooplank- 

 ton IV. The forms of nitrogen excreted by 

 Calanus. J. Mar. Biol. Assoc. U.K. 47:113-120. 



DuGDALE, R. C, and J. J. GOERING. 



1967. Uptake of new and regenerated forms of 

 nitrogen in primary productivity. Limnol. Ocean- 

 ogr. 12:196-206. 



DUGDALE, R. C, J. J. GOERING, AND J. H. RyTHER. 



1964. High nitrogen fixation rates in the Sargasso 

 Sea and the Arabian Sea. Limnol. Oceanogr. 

 9:507-510. 



Emmet, R. T. 



1969. Spectrophotometric determination of urea 

 and ammonia in natural waters with hypochlorite 

 and phenol. Anal. Chem. 41:1648-1652. 

 Eppley, R. W., A. F. Carlucci, 0. Holm-Hansen, 

 D. KiEFER, J. J. McCarthy, and P. M. Williams. 

 In press. Evidence of eutrophication in the sea near 

 southern California coastal sewage outfalls. 

 Calif. Coop. Oceanic Fish. Invest., Rep. 

 FORSTER, R. P. 



1967. Osmoregulatory role of the kidney in carti- 

 laginous fishes (Chondrichthyes). In P. W. Gil- 



1273 



