NOTES 



Comparative Standing Stocks of 



Mesozooplankton and Macrozooplankton 



in the Southern Sector of the California 



Current System 



The long-term (40-year) time series of the Cah- 

 fornia Cooperative Oceanic Fisheries Investiga- 

 tions (CalCOFI) program has characterized low 

 frequency changes in ocean circulation, macro- 

 zooplankton biomass, and ichthyoplankton and 

 holozooplankton populations (Reid et al. 1958; 

 Brinton 1981; Chelton et al. 1982; Smith 1985; 

 McGowan 1985; Roesler and Chelton 1987). The 

 Atlas series of the CalCOFI program provides 

 extensive summaries of the hydrography of the 

 California Current system and the large-scale 

 distribution of its planktonic fauna (Atlas Nos. 

 1-30, Scripps Institution of Oceanography 

 1963-82). These investigations constitute an 

 excellent foundation for studies ranging from 

 experimental work with individual pelagic 

 species to projections of global climate effects on 

 ocean populations and production. 



The primary emphasis of the zooplankton com- 

 ponent of the CalCOFI program has been the 

 larger macrozooplankton (>505 |xm) and the 

 ichthyoplankton. In the present study, we assess 

 the biomass of the mesozooplankton (defined 

 here as the zooplankton fraction passing through 

 a 505 |xm mesh net but retained in a 202 p.m 

 mesh net) in comparison with that of the histori- 

 cally sampled macrozooplankton. Efforts to close 

 budgets of material and energy in the California 

 Current system (Roemmich 1989) may require 

 consideration of the contributions of the meso- 

 zooplankton to standing stocks and metabolic 

 transformations. Further, given the selective 

 nature of predation by planktivorous fish in this 

 region (Arthur 1976; Koslow 1981), the meso- 

 zooplankton may be disproportionately signifi- 

 cant as prey items to particular size classes of 

 pelagic predators. 



Materials and Methods 



Comparisons of mesozooplankton and macro- 

 zooplankton standing stock were carried out be- 

 tween September 1986 and May 1987. A verti- 

 cally retrieved 6ongo (VERB) net frame was 

 used to take paired zooplankton samples (Fig. 1). 



The net incorporated features of the Brown and 

 Honegger (1978) vertical net and the McGowan 

 and Brown (1966) oblique bongo net, with sev- 

 eral differences. Unlike the Brown and Honeg- 

 ger net, the net rings did not hinge and pre- 

 sented less surface area. In contrast to the bongo 

 net, the VERB frame did not pivot around a 

 central axis, and the system was designed to 

 filter only during vertical ascent rather than dur- 

 ing obhque descent and ascent. The net mouth 



h^ 0.71m ^ 



3.78m 



Figure 1. — Illustration of VERB frame and nets. 



Manuscript accepted May 1989. 

 Fishery Bulletin, U.S. 87:967-976, 1989. 



967 



