FISHERY BULLETIN: VOL. 80, NO. 2 



Bacterioplankton studies in the northwest 

 Africa upwelling ecosystem (Watson 1978) esti- 

 mated the phytoplankton biomass in the water 

 column to be much larger than bacterial biomass 

 at stations <350 m water depth. The bacterial 

 biomass in the sediments, however, was higher 

 nearshore and lower offshore. The water column 

 contained only 8% of the bacterial biomass on the 

 inshore stations, so the bacteria are probably re- 

 cycling only about 0.5 mg-at N/m 2 per day in- 

 shore. The offshore region has about 73% of the 

 bacterial biomass in the water column compared 

 with the sediments, so the bacterioplankton may 

 regenerate as much as 4.4 mg-at/m 2 per day in 

 the deeper waters of 200 m or greater. The bac- 

 terial processes that were occurring in the sedi- 

 ments were estimated from bell jar experiments 

 (Rowe et al. 1977). The inshore bottom ammo- 

 nium release rates (5.64 mg-at/m 2 per day) 

 include bacterial, meiofaunal, and chemical pro- 

 cesses occurring in the sediments, so these values 

 were used rather than the purely bacterial rates 

 of Watson (1978). The difference between the bell 

 jar and bacteria-only rates is about 5.1 mg-at/m 2 

 per day. This difference is quite high to explain 

 as a chemical rate so meiofaunal rates evidently 

 are quite important. In offshore waters the sedi- 

 ment release rates are much lower than inshore 

 based on near-bottom ammonium gradients and 

 decreased ammonium pore water concentra- 

 tions. 



The sparids in this study, Mediterranean Sea 

 reef fish (Whitledge 1972), and the nearshore 

 and bottom fish of British Columbia( Wood 1958) 

 have apparently much smaller weight-specific 

 ammonium excretion rates than fish such as the 

 Peruvian anchovy, northern anchovy, jack 

 mackerel, and sardinella. The increased meta- 

 bolic rate needed by mackerels and clupeoids is 

 probably a result of their large energy demands 

 resulting from continuous swimming. Low 

 metabolic rates in sluggish mammals have been 

 shown to be related to their relatively infrequent 

 movements (Whittow 1977) compared with 

 highly active animals of similar body weight. As 

 a result it could be predicted that respiration or 

 excretion rates for fish should be related to both 

 their body weight and index of locomotion such 

 as swimming speed or daily swimming time. 



The total amountof ammonium regenerated in 

 the upwelling ecosystem off northwest Africa 

 has spatial variability which cannot be ignored. 

 Nevertheless, regeneration in organisms from 

 bacterioplankton through benthos (Table 4) is 



estimated to recycle significantly large amounts 

 of nitrogen in the ecosystem and easily produce 

 all of the ammonium used in primary produc- 

 tivity. In some shallow locations ammonium is 

 produced in large quantities and biological up- 

 take is reduced such that high concentrations of 

 ammonium are often observed in the very near- 

 shore water. 



ACKNOWLEDGMENTS 



This work was supported mainly by National 

 Science Foundation Grant OCE-78-05737 as a 

 component of the United States IDOE Coastal 

 Upwelling Ecosystems Analysis (CUEA) Pro- 

 gram. The analysis was also partially supported 

 by the United States Department of Energy 

 under Contract No. DE-ACO2-76CH00016. 



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