FISHERY BULLETIN: VOL. 69, NO. 3 



biomass in the Subarctic Region, which was 

 roughly three times higher in summer than in 

 February or March (Donald S. Day, unpublished 

 data) .' If phosphate regeneration accounted for 

 all the residual changes in summer, 45 to 50 ""f of 

 the phosphate in the water would be renewed by 

 regeneration in 3 months. In contrast, the 

 upwelled phosphate supplied only about 6'^f of 

 the total concentration in summer of 1966 and 

 phosphate was lost from the upper layers in 1967 

 by mean velocities downward. According to the 

 computed values (Table 4) , however, in the sum- 

 mer the residual change of phosphate was 

 roughly twice that removed from the water by 

 plants. If the residual change is assumed to 

 be mostly due to regeneration, therefore, the 

 zooplankton would have had to release twice as 

 much phosphorus as was taken up by the algae 

 during the same period. A more likely expla- 

 nation is that more phosphate was supplied from 

 below than is indicated by the P,, values and the 

 consequent residual changes would be less. In 

 either case, in situ regeneration by zooplankton 

 appears to be a major source of nutrients sup- 

 plied throughout the summer in the mid-Sub- 

 arctic Pacific Region. 



At Ocean Station "P" primary productivity 

 accounted for the entire loss of phosphate be- 

 tween March and August (Parsons, 1965),° sug- 

 gesting that regeneration was negligible. But, 

 since zooplankton at Station "P" was sufficiently 

 abundant to graze the phytoplankton to a stable 

 level (McAllister, Parsons, and Strickland, 

 1960), it would seem that some phosphate re- 

 generation should have occurred. 



RELATION OF ZOOPLANKTON 



BIOMASS TO CHLOROPHYLL AND 



PRIMARY PRODUCTION 



Data on zooplankton abundance and chloro- 

 phyll were compared to determine if these two 



' Donald S. Day, Oceanographer, Natl. Mar. Fish. 

 Serv. Biol. Lab., Seattle, Wash. 



" Parsons, T. R. 1965. A general description of some 

 factors governing primary production in the Strait of 

 Georgia, Hecate Strait and Queen Charlotte Sound, 

 and the N.E. Pacific Ocean. Fish. Res. Board Can., 

 Manuscr. Rep. Ser. (Oceanogr. Limnol.) 193, 34 p. 

 (Processed.) 



variables were correlated. The smaller zoo- 

 plankters were sampled by raising a y^-m NOR- 

 PAC net (mesh opening 0.33 mm) vertically 

 from 150-m depth to the surface at about 1 m/sec. 

 Displacement volumes of the catches weighted 

 for distance between stations were averaged be- 

 tween lat 46° N and 51°40' N for each cruise. 

 The mean volumes in February and March were 

 about 0.070 ml/m'' of water strained and ranged 

 from about 0.250 to 0.280 ml /m^ in summer, 

 except in August 1967 when the mean volume 

 was 0.550 ml/m^ (Day, see footnote 8). Thus, 

 the zooplankton standing stock increased to about 

 four times its winter level sometime after the 

 phytoplankton increase in March. Grazing by 

 the zooplankton apparently occurred early 

 enough to crop down the algae, thereby limiting 

 ])rimary productivity before it reached suffi- 

 ciently high levels to deplete the nutrients from 

 the upper layers. A relatively steady state of 

 grazing pressure and phytoplankton standing 

 stock seemed to hold during the summer (at least 

 in summer 1966). These findings agi-ee with 

 the conclusion of McAllister et al. (1960) that 

 zooplankton grazing limited primary production 

 at Ocean Station "P" by maintaining the phyto- 

 plankton standing stock at relatively low con- 

 centrations. 



The relation between zooplankton displace- 

 ment volumes and chlorophyll a concentrations 

 (Figure 8) shows a negative correlation, further 

 corroborating the above conclusion. The regres- 

 sion of chlorophyll a on zooplankton includes only 

 those stations north of lat 46° N, except in coastal 

 water and Adak Bay, and excludes all winter 

 data. As shown previously the nearshore and 

 transition waters exhibit chemical and biological 

 features, which indicate ecological areas some- 

 what distinct from the area between. The winter 

 data were also excluded from the regression be- 

 cause productivity was limited by insufficient 

 light. Chlorophyll a concentrations south of lat 

 46° N showed no apparent relation to the amount 

 of zooplankton present. Chloi-ophyll in Adak 

 Bay and coastal waters was always significantly 

 higher than estimated from the regression, ex- 

 cept in March in Adak Bay. All of the high 

 chlorophyll values were near shore and associ- 

 ated with intermediate quantities of zooplankton. 



610 



